Transcript for:
Introductory Chemistry

in this video we're going to focus on chemistry we're going to go over some of the basic topics that you need to know if you're about to take a course in chemistry so let's begin let's start with the periodic table so you need to know the names of the elements the groups and some other properties so in the first column you have h which represents hydrogen and then lithium sodium potassium rubidium now hydrogen is a non-metal but the other ones below that the lithium sodium potassium rubidium and even cesium those are known as alkaline metals the alkali metals are the most reactive of the metals in the periodic table if you let's say put sodium in water it will react violently now the elements in this row they all have one valence electron therefore they like to form ions with plus one charges now in the next column we have elements such as beryllium magnesium calcium strontium barium these are known as the alkaline earth metals these metals are reactive as well but they don't react as violently as the alkali metals now the alkali earth metals they have two valence electrons the valence electrons are those electrons that are in the outermost energy level of an atom the inner electrons are known as the core electrons the alkali earth metals they like to form ions with a plus two charge metals they like to give away electrons as they release electrons they will form a positively charged ion known as a cation the vertical columns are known as groups in the periodic table so the alkali metals is group 1a the alkali earth metals is group 2a the rows are the period this is period 1 period 2 period 3 and so forth next to potassium and calcium you have the transition metals you have uh scandium titanium vanadium chromium manganese iron cobalt nickel copper and zinc below copper you have silver and gold below zinc you have a cadmium and mercury mercury's hg next to silver you have palladium and platinum these are some common elements that you want to know the name of now the transition metals they have variable charges at least most of them do for example iron can be in the plus two or plus three oxidation state copper is typically plus one or plus two so they have variable charges but some of the transition metals like zinc have a common charge of plus two ninety-nine percent of the time zinc has a charge of plus two same is true for cadmium silver is usually plus one gold could be plus one or plus three mercury could be plus one or plus two so you need to know the charges of some of these ions cobalt is usually between plus two and plus three manganese could vary from plus two to plus seven chromium typically as a monoatomic ion plus two and plus three so those are the transition metals so let's say this is the transition metal area over here you have group one and group two then in this region you have the inner transition metals the top part is known as the lanthanides and the group below that represents the actinides and then you have the elements on this side which we're about to go over so groups 1 to 2a then groups 13 to 18 these are known as representative elements group 3 to 12 is the transition metals and then this is the inner transition metals which are non-representative elements now let's focus on groups 13 to 18. group 13 is also known as group 3a and the elements in this group are boron aluminum gallium indium and thalium next to boron you have carbon and below that silicon germanium tin and lead this is group four a the group three a elements they have three valence electrons and most of them like to form plus three charges for example aluminum likes to form a plus three charge ion same is true for gallium but gallium i've seen the plus one and plus three state for indium it can be plus one or plus three and the same is true for thalium but aluminum usually doesn't form the plus one ion it's for the most part plus three now for the group four elements silicon for example can have a plus two or plus four oxidation state these elements have four valence electrons germanium tin and lead you'll see that they can also have a plus two charge or a plus four charge next we have nitrogen phosphorus selenium i mean that's the line i'm going to take that back below phosphorus is arsenic sb is antimony and bi is bismuth so make sure you know the names of the elements because typically that's your first quiz in a regular chemistry course so this is group 5a these elements they have 5 valence electrons however they like to form negative 3 charges these are the non-metals at least most of them are nitrogen likes to form a minus three charge and the same is true for phosphite or phosphorus as an element it's called phosphorus but when it has a negative three charge it's called phosphite n as an element is called nitrogen but as an ion with a negative three charge it's called nitride with the ide ending the next group group 6a or group 16. these elements they have six valence electrons and they like to form ions with a negative two charge negatively charged ions are known as anions so we have oxygen sulfur selenium tellurium and polonium these are known as the calcagens next to that you have the group 7a elements or group 17 and you have fluorine chlorine bromine iodine or iodine and acetene so these have 7 valence electrons and they like to form negative one charges so as ions it's fluoride chloride bromide and iodide o with a negative charge or negative two charges oxide sulfide selenide and so forth the halogens are the most reactive nonmetals as we said before metals they like to give away electrons so metals are they form good reducing agents non-metals like to accept or acquire electrons so non-metals are usually good oxidizing agents non-metals like halogens are very very reactive fluorine is the most reactive non-metal francium is one of the most reactive metals which is on the other side of the periodic table below cesium the alkaline metal you have francium because fluorine really wants to have electrons it is electronegative electronegativity increases towards flooring so as you go up and as you go to the right electronegativity increases so what this means is that fluorine has a very strong desire for electrons fluorine's desire for electrons is greater than that of oxygen and chlorine so non-metals tend to be electronegative metals are usually electropositive electronegative elements once they acquire the electrons that they want they form negative charges electro positive elements like metals they like to give away electrons and they're going to develop a positive charge now group aa or group 18 this represents the noble gases so over here you have helium helium has two valence electrons it doesn't have eight the first row elements they can only have a maximum of two electrons in their first energy level elements in the second row can have up to eight electrons in their energy levels or in their second energy level neon has eight valence electrons and then below neon you have elements such as argon krypton xenon and radon the noble gases are chemically inert they're very stable they don't really participate much in chemical reactions so if you get a test question and ask you which element is non-reactive carbon nitrogen fluorine or neon your answer is neon now let's say if you get a question that asks you which of the following elements is or shares the same chemical reactivity or is most similar chemically speaking let's say they have nitrogen oxygen sulfur fluorine and neon whenever you have two elements in the same column they share similar chemical properties so in this case oxygen and sulfur are chemically similar because they're both calculus they're in the same column so fluorine and chlorine are chemically similar to each other they're both halogens they have the same number of valence electrons and so their chemical reactivity is similar now you need to know where the metals and the nonmetals are with respect to the periodic table so if you look at a typical periodic table you're going to see like a line which goes like this to the lower left of that line you have metals on the upper right side you have nominals so elements like oxygen fluorine sulfur chlorine these are all non-metals the elements like indium gallium lead aluminum those are metals and then in between you have metalloids the most two common metalloids that you'll see in chemistry are silicon and germanium those are the most common metalloids that you'll be tested on metals conduct electricity metals can also conduct heat as well metals are malleable they could be hammered into sheets and they're ductile they can be drawn into wires non-metals do not conduct electricity metalloids they conduct a small amount of electricity non-metals are insulators metals are conductors metalloids they're conductors but with a very high resistance or electrical resistance so metalloids they conduct only a very very small amount of electricity now which metalloid do you think conducts more electricity silicon or germanium as you travel to the left and down across the periodic table the elements become more metallic metallic character increases this way so which one behaves more like a metal silicon or germanium so carbon for the most part is considered to be a non-metal silicon and germanium or metalloids tin think of a tin can tin metal well tint is a metal lead is a metal so as you go down across the periodic table the elements are becoming more metallic which means that the electrical conductivity is increasing so lead can conduct electricity better than tin tin metal can conduct electricity better than germanium so germanium even though it's a metalloid can conduct electricity better than silicon because germanium has more metallic character than silicon now carbon has different forms known as allotropes carbon has carbon can be in the form of diamond which does not conduct electricity at all but diamond is an excellent conductor of heat or carbon could be in graphite which you can find it in pencil light carbon graphite does conduct electricity so make sure you're aware of that so the metalloids are silicon germanium arsenic antimony te born for the most part is considered to be a metalloid but the most common are silicon and germanium and now the next thing that we need to go over are the diatomic elements hydrogen in its natural state doesn't exist as h hydrogen exists as h2 it's diatomic so it exists as a molecule nitrogen is diatomic then you have oxygen fluorine chlorine bromine and iodine these are all diatomic and this is something you just have to know hydrogen is a gas at room temperature nitrogen is a gas oxygen is a gas fluorine is a gas chlorine is like a greenish gas bromine is a red liquid and iodine is a purple volatile solid iodine under normal standard temperature and pressure conditions even though it's a solid it can sublime directly into a gas whenever a substance go from a solid to a gas it's known as sublimation so make sure you know your seven diatomic elements now the next thing that we need to go over are bonds covalent bonds and ionic bonds so what exactly is an ionic bond and what is the difference between a covalent bond and ionic bonds consider the reaction between sodium metal and chlorine so let's say if we have an atom of chlorine as opposed to a diatomic molecule sodium has one valence electron and chlorine has seven valence electrons now as we mentioned before metals they like to give away the electrons non-metals like to acquire electrons so sodium is going to give away its one electron to chlorine sodium loses that electron it becomes a positively charged cation chlorine on the other hand now it has eight valence electrons and so it becomes a negatively charged anion whenever you have two like charges next to each other these two will feel a force that repels them opposite charges well like charges repel but opposite charges attract now sodium it has a positive charge chlorine has a negative charge so these two ions they feel a force of attraction that keeps them together it is that electrostatic force of attraction that holds the ionic bonds together so remember ionic bonds are associated with a transfer of electrons they're composed of ions that are attracted to each other and also typically not always but generally speaking you can identify them because they contain a metal and a non-metal whenever you mix a metal and a non-metal together they react in such a way to form ionic bonds now in a covalent bond the electrons are shared for example let's say if we have two hydrogen atoms each with one valence electron these hydrogen atoms will react in such a way to create a bond and in this bond there are two electrons those two electrons are shared between the two hydrogen atoms and so this is a covalent bond since we have sharing of electrons now because the elements are identical because they have the same electronegativity this is classified as a nonpolar covalent bond because the electrons are distributed equally it's nonpolar now let's say if we have two dissimilar elements for example hydrogen and fluorine now these are both non-metals two nonmetals typically form a covalent bond now hydrogen is going to donate one electron to form the bond and fluorine is going to donate one so hf looks like this now fluorine is significantly much more electronegative than hydrogen so fluorine is going to pull the electrons toward itself so because the electrons are shared unequally the bond is going to be considered a polar covalent bond as fluorine pulls the electrons toward itself it's going to acquire a partial negative charge and hydrogen since it loses some of those electrons it's going to acquire a partial positive charge whenever you have a neutral molecule but where one side is partially positive and the other is partially negative you have a polarized substance you have a dipole to draw the dipole the arrow has to point towards the more electronegative atom the electronegativity of fluorine if you look it up in the table most textbooks would say 4.0 and for hydrogen 2.1 whenever the electronegativity difference if it's greater than 0.5 or if it's equal to or greater than 0.5 the bond is considered to be polar if it's less than 0.5 it's usually nonpolar so whenever you have separation of charge within a molecule you have a polarized molecule now consider this bond between carbon and nitrogen do you think this bond is polar or nonpolar carbon has an electronegativity value of 2.5 and for hydrogen is 2.1 now both of these elements are nonmetals so we have a covalent bond we just need to decide if it's polar or nonpolar the en difference is 2.5 minus 2.1 so it's about 0.4 therefore this bond is considered to be relatively nonpolar since the en difference is not 0.5 or more so anytime you have a molecule that contains only carbon and hydrogen atoms automatically you know it's a non-polar molecule now it's time to take a mini quiz let's see if you remember what you've learned so far classify the following compounds as ionic or covalent feel free to pause the video as you work out these examples so mgo magnesium oxide is it ionic or covalent magnesium is a metal it's found on the left side of the periodic table oxygen is a non-metal whenever you have a metal and a nominal combined this is going to be ionic co2 carbon dioxide carbon is a non-metal oxygen is nominal when you have two nonmetals you have a covalent molecule if it's covalent typically it's usually molecular so you can also classify it as a molecular compound it's composed of molecules now what about water hydrogen is a non-metal oxygen is a non-metal so this is classified as covalent for lithium chloride lithium is on the left side of the periodic table and that's a metal chlorine is a be careful because hydrogen is on the left side but hydrogen is not classified as a metal hydrogen and lithium are in the same column but lithium is a metal hydrogen is not metal so this is ionic fluorine is composed only of non-metals so this is covalent now because fluorine is made up of the same element the bond between those two elements is a nonpolar covalent bond because the en difference is zero now the bond between carbon and oxygen that's a polar covalent bond because the e n difference is much greater than 0.5 and between oxygen and hydrogen and that's also a polar covalent bond now you need to be careful with the exceptions for example let's say if you have magnesium sulfate what type of bonds are found in this compound magnesium has a plus two charge sulfate is a polyatomic ion with a negative two charge so because we have ions we just have an ionic bond the ionic bond is between the magnesium ion and the sulfate ion as you can see magnesium is a metal and sulfur and oxygen are composed of nonmetals now within the sulfate ion you have covalent bonds the bond between oxygen and sulfur is covalent sulfur is a non-metal oxygen is a nominal both of these elements are found in the upper right corner of the periodic table so that's a covalent bond between the oxygen and the sulfur so if you have a compound that contains a metal and a nonmetal and that also has a polyatomic ion poly means many a polyatomic ion is an ion with many atoms so if you have a metal with a polyatomic ion it has ionic and covalent bonds now there are some ionic bonds that don't have metals a good example is the ammonium ion if you see nh4 is something like ammonium chloride this is ionic the nh4 plus ion is a polyatomic ion and chlorine has a negative charge so here we have ions with charges so this is an ionic bond but within the ammonium ion the bonds between hydrogen and nitrogen both of them are nonmetals so this is a covalent bond so ammonium chloride has ionic and covalent bonds but there's no metals so most compounds that are composed of metals and non-metals are ionic but there are some that you have to watch out for that do not contain metals now the next thing that we need to talk about is atomic structure the structure of the atom but let's go over some things on a periodic table so c represents carbon and if you look at the symbol for carbon there's two numbers one above it and one below it the smaller of the two numbers is the atomic number the atomic number is equal to the number of protons now for a neutral atom the number of electrons and protons are the same for ions ions are particles with unequal number of electrons and that's why they have a net charge the bottom number is the average atomic mass of all of the isotopes of carbon now don't confuse isotopes with allotropes i'll explain what isotopes are so this number let's say if we have the carbon-12 isotope this is the mass number the mass number is the sum of the number of protons and neutrons so an element of carbon has six protons so the nucleus which contains the protons and the neutrons the nucleus has a net charge of plus six protons are positively charged electrons are negatively charged and neutrons are neutral now a neutral atom of carbon has six electrons in the first energy level there are two electrons in that energy level the first level can only hold a maximum of two the second level can have up to eight so the second level contains the four electrons that i remain in so carbon has a total of six electrons notice that carbon is in group four a of the periodic table therefore it has four valence electrons the four valence electrons are the electrons in the outermost energy level of carbon the two electrons on the inside are known as core electrons here's a question for you in the nucleus of a helium atom helium has a mass of four an atomic number of two in this form it looks like the atomic number and the mass number switched but the lower of the two numbers is the atomic number helium has two protons two neutrons so in the nucleus the protons carry a plus charge the neutrons are neutral and helium only has two electrons which are valence electrons because it only has one energy level now we know that opposite charges attract so the electrons and the protons they're attracted to each other so the electrons feel a force that keeps it rotating in a circle whenever you have a force that directs a particle towards the center of the circle it's called the centripetal force and it keeps it rotating in a circle so even though the particle may be moving to the right the electron is going to stay in a circle because of the centripetal force which is caused by the electrostatic force between electrons and the protons a centripetal force always keeps an object in a circle if you think of the moon why it orbits the earth the gravitational force that pulls the moon towards the earth keeps the moon in orbit around the earth and that gravitational force is acting as a centripetal force i know we'll kind of jump into physics here but it's a good time to talk about it now if opposite charges attract each other then like charges must repel each other so how is it that the nucleus remains intact when you have these two protons that are so close next to each other shouldn't they fly apart due to the electrostatic force that wants to push them away from each other it turns out that there's a strong nuclear force that keeps the protons together and that must be a very very strong force if you split the atom a lot of energy will be released which is a nuclear reaction but the strong nuclear force keeps the protons together inside the nucleus now let's go over some examples let's say if we have an element of fluorine fluorine has an atomic mass of 19 and an atomic number of nine how many protons neutrons and electrons are in this fluorine atom so let's write some equations to find the number of protons it's simply equal to the atomic number the number of neutrons is the mass number minus the atomic number and the number of electrons is the atomic number minus the charge if there was a charge it would be right here but if there's no charge we have a neutral atom which means the protons and electrons are equal so the atomic number is nine which means that fluorine has nine protons the mass number is 19 but the difference gives you the number of neutrons 19 minus 9 is 10 so fluorine has 10 neutrons the number of electrons is the atomic number minus the charge since the atom is neutral it doesn't have a charge so it's nine minus zero therefore there are nine electrons in this atom now out of the nine electrons how many electrons are valence electrons fluorine has seven valence electrons you can find this number based on the group that fluorine is located in fluorine is located in group 7a which is the same as group 17 and so it has 7 valence electrons so how many core electrons does it have the total must be nine so nine minus seven is two so fluorine has two core electrons but seven valence electrons for a total of nine electrons consider arsenic which has an atomic number of 33 and a mass number of 75 how many protons neutrons electrons core electrons and valence electrons are found in an atom of arsenic so because the atomic number is 33 arsenic has 33 protons the number of the neutrons is the difference between 75 and 33 75 minus 33 is 42 so arsenic has 42 neutrons now because we have an atom of arsenic which is neutral it doesn't have any charge the number of protons and electrons are the same now how many valence electrons does arsenic have so arsenic is found in group 5a of the periodic table so therefore arsenic has 5 valence electrons so how many core electrons does it have so 33 minus 5 is 28. therefore arsenic has 28 core electrons so the core electrons plus the valence electrons must add to the total number of electrons now let's try another example aluminum has an atomic number of 13 and a mass number of 27 and we're going to focus on the aluminum plus 3 cation how many protons electrons and neutrons are found in this particular ion so the atomic number is 13 therefore it contains 13 protons the difference between the mass number and the atomic number 27 minus 13 is 14 so it has 14 neutrons now the number of electrons in this ion is the atomic number minus the charge so 13 minus 3 is 10 so it has 10 electrons if you add up the the charges we have a charge of 13 from the 13 protons and a charge of negative 10 from the 10 electrons 13 minus 10 is plus 3 which is the net charge of the ion now what if we have a negatively charged ion let's say if we have the phosphide ion which has an atomic number of 15 and a mass number of 31. how many protons electrons and neutrons are in this ion so because the atomic number is 15 it has 15 protons the atomic number or the number of protons identifies the element now 31 minus 15 is 16 so it has 16 neutrons to calculate the electrons is the atomic number minus the charge 15 minus negative 3 is the same as 15 plus 3 which is 18 electrons so if you add up the charges we have a net charge of positive 15 from the 15 protons and then that charge of negative 18 from the 18 electrons so the overall charge 15 plus negative 18 is negative three so whenever an ion has more electrons than protons it has a net negative charge if it has more protons than electrons then the overall charge is positive now let's go over the different types of isotopes of carbon the most two common isotopes of carbon is carbon 12 and carbon 13. chemically speaking these atoms of carbon behave the same way they're both elemental carbons isotopes they have the same chemical reactivity but their nuclear properties are different because the nucleus is different but the number of electrons is the same and the number of protons the same now how many protons are found in each of these two isotopes of carbon both contain six protons to find the number of neutrons is the mass number minus the atomic number so the one on the left contains six neutrons the one on the right has seven neutrons 13 minus six is seven but because these are both atoms of carbon that means that they're electrically neutral the number of electrons are the same so you need to know how isotopes differ from one another isotopes they have the same atomic number the same number of protons and they're made up of the same element in this case elemental carbon so that's how they're similar but how are they different isotopes they differ in a mass number and they differ in the number of neutrons so therefore they're different in their nucleus so they have different nuclear properties carbon 12 is stable but carbon 13 decays over time now if you look at the periodic table at elemental carbon you'll see that the mass number is not exactly 12 it's like 12.01 and as we mentioned before this is the average atomic mass of all of the carbon isotopes you also have carbon 14 but that's very very rare approximately 99 of carbon atoms is the carbon-12 isotope and about one percent is carbon 13. so let's say if you have a sample of 100 carbon atoms 99 of those carbon atoms will be carbon-12 and one would be carbon 13. if you have a thousand carbon atoms 990 would be carbon 12 10 would be carbon 13 since one percent of a thousand is ten you can calculate the average atomic mass by using a weighted average the average atomic mass is equal to the mass of the isotope times its relative percent abundance plus the mass of the other isotope times its percentage now if you have a third isotope it's going to be plus m3 p3 and if there's more this can keep going on forever but we can calculate the average based on those two isotopes the mass of the first carbon atom carbon 12 is 12 the percentage is 99 99 as a decimal is 0.99 to convert percent to a decimal divided by 100 or simply move the decimal point two units to the left now carbon 13 has a mass of 13 but a percentage of 0.01 so if you multiply 12 by 0.99 you're going to get 11.88 if you multiply 13 by 0.01 it's going to be point 13 and if you add point 13 plus 11.88 you should get 12.01 which is the average or the weighted average atomic mass of all of the carbon isotopes that are naturally found on earth now what about boron boron has an average atomic mass of 10.81 and it's element 5 on the periodic table now boron has two principal isotopes boron 10 and boron 11. notice that the average is between 10 and 11. so if you have the two isotopes and the average atomic mass how can you use that information to find the relative percent abundance of these two isotopes so in nature or on earth what percentage of boron atoms is the b10 isotope and what percentage is the b11 isotope so we're going to start with the same equation so the average is equal to m1 p1 plus m2 p2 so the average is 10.81 the mass of the first isotope is 10 and the percentage we're going to call it x now it's important to understand something let's say if the b10 isotope is 70 that means that 30 is 11. so if x corresponds to 0.70 then .30 must be 1 minus x because 1 minus 0.30 i mean 1 minus 0.70 is point thirty so notice that x plus one minus x adds up to one and one represents a hundred percent m2 is the mass of the second isotope which is 11 and as you mentioned the percentage is going to be 1 minus x so we need to solve for the value of x so it's going to be 10x and if we distribute the 11 11 times 1 is 11 and 11 times negative x that's negative 11x so now we need to add like terms so the two like terms are 10x and negative 11x 10 minus 11 is negative 1 or simply negative x and now at this point we need to subtract both sides by 11. now let's make some space 10.81 minus 11 is negative point 19. those two numbers cancel so negative point 19 is x if you multiply both sides by negative one x is point nineteen which corresponds to 19 now x was associated with the b10 isotope so we have 19 percent of boron 10 100 minus 19 is 81 so that is the relative percent abundance of the other isotope b11 so notice that we have more of the b11 isotope than boron 10 and it makes sense because the average is closer to 11 than it is to 10. 10.81 is close to 11 so we have more of the boron 11 isotope so this is how you can calculate the relative percent abundance of an isotope within an element what we're going to do now is have a pop quiz on the properties of the elements in the periodic table so consider the following elements iron metal magnesium bromine aluminum and lithium so which of the following is a transition metal what do you think the answer is fe is a transition metal it's between groups three and twelve now which of the following elements is the most reactive metal listed here the most reactive metal is typically an alkali metal and lithium is the only alkali metal in this group lithium is found in the first column of the periodic table now which one is a non-metal which element is found in the upper right corner of the periodic table this is bromine bromine is nominal now which of the following elements is an alkaline earth metal magnesium is an alkaline earth metal it has two valence electrons and it's in the second column of the periodic table now which the following elements has three valence electrons is it fe mg bromine aluminum or lithium it turns out aluminum which is found in group 3a or group 13 has three valence electrons consider these elements zinc bromine silicon iodine and fluorine now these are diatomic which are the following elements is a liquid at room temperature is it zinc bromine silicon iodine or fluorine bromine is a red liquid now which the following elements has the greatest electrical conductivity it turns out zinc has the greatest electrical connectivity because it's the only metal that's listed here now which of the following elements is a metalloid silicon is a metalloid it's used to make solar cells which convert light energy into electricity now which of the following is a solid at room temperature iodine is a purple solid and which one is a gas fluorine is a gas at room temperature consider these elements as well argon uranium chromium iron metal and sulfur well let's write sulfur as s8 so which the following elements is attracted to a magnet which element can be magnetized it turns out iron metal is ferromagnetic that's the symbol fe iron metal if you put it next to a magnet it's going to stick to the magnet now which element in its ionic form forms colored solutions particularly different colors most transition metals will form colored solutions but the most common one is chromium chromium has multiple oxidation states and it forms a variety of colors now iron metal is a transition metal so a2 can form a variety of colors but chromium takes it to another level chromium has a lot more colors than fe now which of these elements is an inner transition metal uranium is an inner transition metal it's part of the actinide series now which of these elements is chemically inert it doesn't really participate in chemical reactions the answer is argon argon is a noble gas and the noble gases are chemically stable they don't like to participate in chemical reactions they have no need of gaining or losing electrons which element is a yellow solid at room temperature but when melted it turns into a blood red liquid and when burned in the presence of oxygen it produces a blue flame which element is that this element is sulfur now consider these other elements mercury gold chlorine carbon and germanium which of the following elements is a liquid at room temperature mercury is a liquid at room temperature it's called quicksilver and it conducts electricity as any metal now which of the following elements is known as a noble metal gold is a noble metal it's very difficult to oxidize it's chemically stabilized gold for the most part most of the precious elements or the precious metals like palladium silver platinum these elements are known as noble metals they're very stable chemically speaking they're very resistant to corrosion and they're very expensive too those noble metals now which of the following elements does not conduct electricity is it mercury gold chlorine carbon or germanium the only one that doesn't conduct electricity is the nonmetal chlorine which is diatomic as cl2 all of the other elements can conduct electricity mercury is a metal so it can conduct electricity and gold is a metal too so gold can conduct electricity as well germanium is a metalloid and so it can conduct a small amount of electricity carbon is a non-metal but it has different forms different allotropes the diamond form of carbon does not conduct electricity however the graphite form of carbon does conduct electricity so the only answer the only element that does not conduct electricity is elemental chlorine now which of the following elements is a gas at room temperature this would also be chlorine chlorine is a gas atom temperature so make sure you know some common properties of the elements in the periodic table you might see them on your next exam here's a question for you helium is it composed of atoms molecules or compounds and what is the difference between an atom and a molecule helium like all the other noble gases are composed of atoms so helium looks like a single particle it's made up of a single atom hydrogen gas is a molecule a molecule is made up of two or more atoms it's a individual particle that has multiple atoms water for example is a molecule and a compound at the same time so water contains an atom of oxygen and two atoms of hydrogen so it looks like that so helium is composed of atoms hydrogen is made up of molecules the molecule is composed of two or more atoms they could be the same type of atom or different atoms water is also classified as a molecule because it contains more than two atoms but also water is known as a compound a compound is a substance that contains two or more different types of atoms or two or more different elements water is a compound because it contains hydrogen and oxygen h2 is not a compound because it contains only one type of element so h2 is classified as a pure element it consists only of elemental hydrogen water is not a pure element it's made up of two different types of elements helium is a pure element it's only made up of helium atoms now what about sodium chloride how would you classify it and let's compare it to water sodium chloride is a compound because it has two different elements but this is not a molecular compound this is known as an ionic compound because sodium chloride is composed of ions whenever you see a metal and a nonmetal it's usually ionic water is a compound as well but it's also a molecule so it's a molecular compound so water is composed of individual particles whereas sodium chloride it's a giant crystal that contains many ions you have sodium ions chloride ions and you have billions of these ions together in a solid so you have a huge network of ions bonded together but in water you have individual particles which makes it a molecule so here's a quiz view i'm going to give you a list of substances and i want you to identify them as being a molecule a pure element being composed of atoms ionic compound or molecular compound so we have co2 argon magnesium sulfide zinc metal and f2 so let's start with co2 how would you classify so this substance is composed of two nonmetals so this is going to be a molecule since it's composed of many atoms but it's also a compound because it's composed of different elements so it's a molecular compound now what about argon argon is a noble gas so it's made up of atoms and it's also a pure element we only have one type of element in this substance magnesium sulfide this is composed of a metal and a nominal so it's ionic and it's a compound so it's a ionic compound anytime you have a compound it's never going to be a pure element zinc is composed of atoms but these atoms are covalently bonded to each other and zinc is a pure element we only have one type of element in the substance fluorine is a pure element but it's also a molecule because it's composed of it's an individual particle that is composed of two atoms so now you know how to classify substances now what is the difference between a pure substance and a mixture a mixture is the combination of two or more pure substances for example if you mix water which is a pure substance with sodium chloride you have a mixture a salt water mixture if you mix hydrogen with helium you now have a mixture so mixture is simply the combination of two or more pure substances sodium chloride is a pure substance even though it's a compound that has two different elements is still classified as a pure substance a mixture can be separated into its components by physical means so for example you can separate water from salt water by evaporation that's a physical process but you can't separate sodium from chlorine in salt by evaporation or by boiling or by some physical process at least not under practical conditions so therefore sodium chloride is not a mixture you can't separate sodium from chlorine using common physical processes you have to use a chemical process to separate the atoms within a compound so remember mixture is simply the combination of two or more pure substances so individually h2 is a pure substance helium is a pure substance but combined it's a mixture so whenever you see this plus it's going to be a mixture now there's two types of mixtures that you need to be familiar with homogeneous mixtures and heterogeneous mixtures consider the two mixtures let's say if we have a salt water solution we have free-flowing sodium and chloride ions in water and on the right side we have an oil water mixture now we know that water and oil don't mix typically oil is less dense than water and so it floats on top which one is homogeneous and which one is heterogeneous the salt water mixture is the homogeneous mixture because the salt water is distributed uniformly throughout the solution and so it's homogeneous if you look at it you'll see one clear distinct solution on the right side we have a heterogeneous solution you can clearly see two distinct phases you can see the oil and the water separately from each other because they don't mix very well they don't mix evenly or at all it's heterogeneous so let's say if you have water and you have sand in the water is it homogeneous or heterogeneous so notice that the sand is not evenly distributed throughout the water you can clearly see two distinct phases you can literally see the sand and the water separate from each other this is a heterogeneous mixture now what about air is air a homogeneous mixture or a heterogeneous mixture air is a mixture of gases air contains mostly nitrogen and oxygen gas about 78 of it is nitrogen and 21 is oxygen the remainder are gases like argon co2 water vapor and some other stuff but these gases are evenly distributed throughout air they're evenly they're mixed with each other um in an even ratio so to speak so for example let's say if you have a room the composition of air in this region is 78 nitrogen 21 oxygen and in this region it's not going to be 50 nitrogen and 50 oxygen it's always going to be 78 oxygen i mean nitrogen and 21 oxygen the distribution of these molecules is even throughout this particular room so therefore air is a homogeneous mixture now let's move on to another topic that is unit conversion you need to know that one mile is equal to 5280 feet one mile is also 1.609 kilometers feel free to take notes in one kilometer there are a thousand meters one meter is about a hundred centimeters and one inch is 2.54 centimeters there's three feet in the yard and 12 inches in a foot one milliliter is equal to one cubic centimeter and a thousand milliliters is equivalent to one liter so these are units for distance for time you know that one year is 365 days one month is approximately 30 days a day is 24 hours an hour 60 minutes and a minute is 60 seconds so these are some common conversions that you want to know so let's say if you have 460 meters how can you convert that to kilometers now the first thing that you want to do is identify the conversion factor that you need the conversion factor between kilometers and meters is this one kilometer is a thousand meters now start with what you're given we're gonna write 460 meters over one in the next fraction you need to place the conversion factor but in the appropriate order so notice that we have meters on the top left that means we need to put the unit meters on the bottom right the number that's associated with meters or that's next to it is a thousand so that a thousand is going to be right next to the meters so on top we're going to put one kilometer so the unit meters cancel and we're going to get km so because the thousand is on the bottom we need to divide instead of multiply so it's 460 divided by a thousand whenever you divide by a thousand simply move the decimal three units to the left so 460 meters is equivalent to 0.460 kilometers let's try another example convert 75 millimeters into centimeters the conversion factor is 10 millimeters is equal to a centimeter so how would you set it up and what's the answer so let's start with what we have which is 75 millimeters now since we have millimeters on the top left we need to put it in the bottom right and the 10 is associated with millimeters so let's put that there and one centimeter is going to go on top so these units cancel and it's 75 divided by 10 which if you move the decimal one unit to the left it's going to be 7.5 centimeters now let's say if we have a multi-step problem for example if you have point 25 kilometers how can you convert that into feet so we know that one mile is equal to 5280 feet and one mile is 1.609 kilometers so we need to convert from kilometers to miles and then miles to feet so how can we do it feel free to pause the video and try this example yourself so let's start with what we're given now in the next fraction we need to put the kilometers on the bottom so that these units will cancel and we want to convert it to meters initially so we know that 1.609 kilometers this is supposed to be miles by the way not meters 1.609 kilometers is one mile so now we can convert miles into feet so we got to put the unit miles in the bottom and one mile is equal to 5280 feet and so the unit miles cancel and this is going to give us the answer in feet so it's 0.25 divided by 1.609 times 5280 and you should get 820.4 feet now let's say if you have a unit of area for example 36 square feet how can you convert it into square yards what can we do so we know the conversion factor there's three feet in the yard so always start with what you're given now in the next fraction we need to put feet on the bottom yards on top so we know there's three feet in one yard but because we have a square here we need to square it so we need to divide 36 by three two times or by nine three squared is nine so the unit feet squared will cancel and we're going to get yard squared so 36 divided by 3 is 12 and 36 i mean 12 divided by 3 a second time is 4. so it's four square yards this is the same as 36 divided by nine which is four now let's try another example let's say if wish to convert 5000 cubic millimeters into cubic centimeters how can we do it so this is a unit of volume whenever it's raised to the third dimension we know the conversion factor is 10 millimeters is equivalent to one centimeter so we're going to put that in the next fraction now for this particular example we need to raise it to the third power so we need to divide 5000 by 10 three times or by 10 cubed which is a thousand 5 000 divided by 10 is 500 500 divided by 10 is 50 50 divided by 10 is five so this is five cubic centimeters or you could say five thousand divided by a thousand is five so now you know how to convert from one unit of volume to another unit of volume how would you convert 30 meters per second into miles per hour which can also be written as mph how can we do it so notice that we have the unit of speed which is meters and seconds we need to put the unit meters on the top of the fraction and seconds on the bottom let's make an outline of what we need to do so we need to convert meters to kilometers and kilometers to miles and then we gotta convert seconds into minutes and minutes into hours so what's the conversion factor for meters and kilometers there's a thousand meters for every kilometer so the unit meters cancel and we know that between kilometers and miles one mile is equal to 1.609 kilometers so kilometers cancel now that we have the unit miles we don't need to change that anymore since that's what we want what we do need to change is seconds into hours so because we have the seconds on the bottom it has to be on the top let's convert second to two minutes there's 60 seconds in one minute and there's 60 minutes in a single hour so the unit seconds cancel and minutes cancel so now we can get the answer so it's going to be 30 divided by a thousand times 60 divided by 1.609 times another 60. so you should get 67.1 miles per hour here's another one convert 25 feet per second into kilometers per hour so let's start with 25 feet over seconds we know how to convert seconds into hours but how can we convert feet into kilometers let's convert feet into miles and then we can convert miles into kilometers if you recall there's 5 280 feet per mile and we know that there's 1.609 kilometers in a single mile so these units cancel and the unit miles cancel and we know there's 60 seconds in a minute and 60 minutes in an hour so seconds cancel minutes cancel as well and so it's going to be 25 divided by 5280 times 1.609 times 60 times 60. and you should get 27 kilometers per hour now the next thing that we need to do is cover the metric system you need to know that terra corresponds to 10 to the 12th power giga is 10 to the 9th power mega represents ten to the six which is a million ten to the nine is a billion kilo is ten to the third which is a thousand now below kilo you have hectare which is ten squared or 100 and deca which is 10 to the first or 10. and below that you have deci which is 10 to the minus one and then centi which is 10 to the negative two and milli which is ten to the minus three and then micro which is ten to the negative six nano that's ten to the negative nine and pico is ten to negative twelve now from this you need to be able to write the conversion factor so for example one kilometer is ten to the three meters so you can write it like this one km is one times ten to the third meters that's your conversion factor or if you want to write the conversion factor for micro you can say one micrometer or um is equal to one times ten to the negative six meters so how would you write the conversion factor for millimeters centimeters and nanometers so let's start with centimeters one centimeter is one times ten to the negative two meters if you multiply both sides by 100 you'll get this conversion factor 100 centimeters is one meter for millimeters we could say one millimeter is one times ten to the minus three meters for nanometers one nanometer is one times ten to the negative nine meters so there's always a one with the prefix and on the other side the multiplier is always associated with the base unit in this case meters let's try an example let's say if we have 170 000 centimeters and we wish to convert it to kilometers using the metric system how can we do it what you want to do is you want to convert centimeters to meters and then meters to kilometers so let's write out the conversion factors one kilometer is one times ten to the three meters which is a thousand meters one centimeter is one times ten to the negative 2 meters these are the two conversion factors that we need so let's start with 170 000 centimeters over 1. let's convert it to meters first so the unit centimeters has to go on the bottom and therefore the unit meters has to go on top using this conversion factor so the unit centimeters will cancel and in the next step we can convert meters into kilometers so we got to put meters on the bottom and kilometers on top so that these units will cancel at this point we could do the math now what's going to happen if we take 10 to the third and move it to the top x to the negative two is the same as one over x squared whenever you move an exponent from one side to the other side it change sign so the positive 3 on the bottom will become negative 3 when it moves to the top so we can rewrite this as seventy thousand times ten to the negative two times ten to the negative three what is ten to the negative two times ten to negative three now what is x cubed times x to the fourth whenever you multiply common bases you are allowed to add the exponents so three plus four is seven this is x to the seven so therefore ten to the negative two times ten to the negative three is ten to the negative five because negative two plus negative three is negative five so now we need to put the number in appropriate scientific notation we need this number to be between one and ten so we need to move the decimal point five units to left one two three four five if we do that this is going to increase by five negative five plus five is zero so it's one point seven times ten to zero anything raised to the zero power is one so the answer is one point seven kilometers another way you can see it is you need to realize that 170 000 is 1.7 times 100 000. and because a hundred thousand contains five zeros a hundred thousand is ten to the fifth and five plus negative five is zero so you get ten to zero which is one and so the answer is one point seven kilometers let's try another example try this one convert 380 micrometers into centimeters feel free to pause the video as you work out this example so let's convert micro into meters and then meters to centimeters so the first thing you want to do is write out the conversion factors that you need micro is 10 to negative 6 so 1 micrometer is 1 times 10 to the negative 6 meters since he is 10 to minus 2. so these are the conversion factors that we need so let's start with what we're given and let's convert micrometers into meters so we need to put the unit micrometers on the bottom so that they will cancel and in the next step we need to put the unit meters on the bottom which will give us centimeters so these units will cancel so now we can do the math so it's going to be 380 times 10 to the negative 6 and then we're going to take this and move it to the top so the negative 2 will become positive 2. negative six plus two is negative four so we have three eighty times ten to the negative four now we need to move the decimal so that it's between the three and the eight the number has to be between one and ten so we need to move it two units to the left whenever you need to move the decimal point to the left you need to increase this number by the number of spaces you move to the left so since we move two units to the left we gotta add two to it so it's gonna be three point eight zero times ten to the negative four plus two is negative two so this is the final answer in centimeters try this one let's say if you have 3.6 times 10 to the 4 kilometers actually instead of kilometers let's make it nanometers convert this number into decimeters so how can you convert 3.6 times 10 to the four nanometers into decimeters so just like before we need to go from nanometers to meters meters to decimeters so let's write out the conversion factors that we need one nanometer is one times ten to the negative nine meters deci is associated with negative one so the one decimeter is one times ten to the minus one meters so let's start with the number that we have and let's convert to meters so we need to put nanometers on the bottom and we got to put 1 times 10 to the negative 9 meters on top and so meters will have to go on the bottom in the next fraction so that these units cancel and we need to put decimeters on top so let's move this number to the top so what we have is 3.6 times 10 to the 4 times 10 to the negative 9 and times ten to the positive one so four plus negative nine is negative five negative five plus one is negative 4 so our final answer is 3.6 times 10 to the negative 4 decimeters notice that we don't need to change this number because 3.6 is between 1 and 10 so it's already in proper scientific notation form let's try this problem an 8.4 gram rock was placed in a graduated cylinder that contained 24.1 milliliters of water the volume went up to 26.2 milliliters calculate the density of the rock the equation for density is mass divided by volume now let's understand what's happening here so let's say if we have a container that has 24.1 milliliters of water and then we're going to add a rock so then the volume is going to increase to 26.2 and so here's the rock what is the volume of the rock so this is how you can find the volume of the rock it's by water displacement the volume of the rock is the difference between these two values so it's 26.2 minus 24.1 which is 2.1 so the amount that the volume increases by that's the volume of the rock and we know the mass of the rock is given to us it's 8.4 and so 8.4 grams divided by 2.1 gives us a density of four point or simply four it's four grams per milliliter now keep in mind one milliliter is the same as one cubic centimeter so we already have the density in grams per cubic centimeter which is the answer to the first part of the question so now we got to find the density in kilograms per cubic meter so we need to convert it so what is the conversion between kilograms and grams one kilogram is a thousand grams kilo represents ten to the third which is a thousand and one meter is a hundred centimeters so let's convert it so there's a hundred centimeters in the meter but we need to raise it to the third power because of the three and to convert grams to kilograms there's one kilogram per thousand grams so the unit grams cancel and cubic centimeters will cancel as well so we have 4 times 100 cubed which is 100 times 100 times 100 and then on the bottom we have a thousand so we can cancel three zeros and so what we now have is four times a hundred times ten and this is simply one which will not change the value of anything so four times a hundred is four hundred times ten that's four thousand so the answer is four thousand kilograms per cubic meter here's another density related unit conversion problem the price of gold is 42 dollars per gram the density of gold is 19.3 grams per cubic centimeter what is the value of a rectangular gold bar that is 1 by 2 by 3 inches so what's the first thing we need to do how can we find the answer to this problem so notice that we have the length width and height of the rectangle so we could find the volume so if you were to draw a picture here's a typical rectangle so let's say we have a width of two i mean a width of one height of two and the length of three the volume of a rectangle is length times width times height since we have the volume which is going to be in cubic inches we can convert that to cubic centimeters and using a density which has grams and cubic centimeters we can convert it to grams and using the price of gold per gram we can convert that to dollars and get the value of this particular gold bar so let's go ahead and do that so first let's find the volume so length times width times height one times two times three the volume is six cubic inches so let's convert it to cubic centimeters keep in mind one inch is equal to 2.54 centimeters and we need to raise it to the third power so that cubic inches will cancel now that we have cubic centimeters let's use the density to convert it to grams one cubic centimeter is equal to 19.3 grams based on this number and the price of gold is 42 per gram so the unit grams cancel and cubic centimeters so now we can get the answer so it's 6 times 2.54 raised to the third power times 19.3 times 42. so this particular gold bar is worth seventy nine thousand seven hundred dollars and twelve cents the next topic in chemistry that we need to talk about is significant figures so the first thing you need to be able to do is you need to be able to determine the number of significant figures within the number so for example 395 has how many significant figures any non-zero number is always counted as a significant figure so we have three significant figures now what about 407 the only thing you have to worry about is the zeros this zero that's between the four and seven is it significant or is it not in between zeros are always significant so this is kind of as three sig figs now what about five thousand fifty so we know the fives are significant and the zero that's between it what about the zero to the right the zeros to the right of a non-zero number are known as trailing zeros trailing zeros are sometimes significant if there's a decimal point since we don't have a decimal point that particular zero is not significant so we only have three sig figs now if we had 5050 with a decimal point then this zero is counted so we have four sig figs try these forty four hundred how many sig figs are in these numbers so here we have a trail in zero and there's no decimal point so we only have one sig fig the same is true for the next one the two zeros to the right are not counted but now that we have a decimal point the zeros to the right of the four are counted so this is four and this is six all of these are counted now what about these numbers point zero one four zero seven point zero zero three zero point zero five seven zero eight zero point zero zero one zero five zero zero and 0.0400 the zeros to the left which are leading zeros are never counted as significant so we can ignore those zeros so here we have an in between zero which is between the four and seven that's counted so we have four sig figs the zero to the right of the three is counting because we have a decimal point so it's two for the next one we have five sig figs since we have a decimal point any zeros to the right of a non-zero number are counted and for this one we also have five sig figs for this one we only have four now what about for scientific notation how many sig figs are there in these numbers because we have a decimal point those two numbers any zeros to the right will be counted so this is two sig figs here we have a total of three and here we have four and in this number we have five sig figs so in scientific notation since you're usually going to have a decimal point the zeros to the right of a non-zero number will be counted and you don't have to worry about the multiplier that's not related to sigfigs so you can just ignore it now you need to know how to round a number to the appropriate number of significant figures when dealing with multiplication division addition and subtraction so let's say if we have 5.38 times 4.1 for multiplication and division you need to round the final answer to the least number of significant figures the first number has three sig figs the second one has two so the final answer should only have two sig figs so first let's get the exact answer 5.38 times 4.1 so the exact answer is 22.058 so how can we round this answer to a number that's close to 22.058 but still has two sig figs so we could say this is approximately 22 which has two sig figs now let's see if we have uh 8.946 divided by 4.13 find the answer and round it to the appropriate number of significant figures so here we have four sig figs and in this number we have three so first let's get the exact answer which is 2.1661 and we can stop there so now we gotta round this number to three significant figures so the first two numbers are going to remain the same the last one the third one this is what we have to decide should we keep it at six or should we round it up to seven to find the answer look at this number if it's five or more you need to round up so the six is going to go up to a seven so we're going to say 2.17 now you need to understand the rules of addition and subtraction so let's say if you want to add 4.32 plus five point six you need to round to the least number of digits to the right of the decimal point which is here so when you add these two numbers you're going to get 9.921 so you need to round to the nearest tenth place so we look at this number since it's less than five we're going to keep it down at nine if it was greater than five or equal to five we would round it up to ten so the answer for this example is nine point nine now let's see if you have fourteen point seven five three minus two point twelve this is going to be three three six two one that's the exact answer but we need to round it at this position to the nearest hundredths place so since this number is less than 5 we're going to keep this at 3 and not round it up to 4. so the answer is 12.63 so for addition and subtraction line it up for multiplication and division round to the least number of significant figures now the next thing that you need to be able to do is you need to be able to name compounds so for example let's say if you wish to write the name of scl2 and mgcl2 how would you do it mgcl2 is called magnesium chloride scl2 is known as sulfur dichloride so why is it that scl2 is sulfur dichloride but mgcl2 is not magnesium dichloride it's simply magnesium chloride why do we use the prefix dye for this molecule but we don't do it for this one the reason being is mgcl2 is ionic it's composed of a metal and a non-metal scl2 is not ionic it's a molecular or a covalent compound for molecular and covalent compounds you need to use the prefixes like mono di tri tetra and so forth mono represents one dies two tries three tetra is four penta is five hexa is six hepta is seven octa is eight nana is nine deca is ten for ionic compounds you don't need those prefixes so let's go over the nomenclature of molecular compounds go ahead and name the following compounds so this one is called tetraphosphorus because there's four phosphorus atoms dicoxide deca is 4 10. now what about this one s e is selenium we don't have to say mono selenium if the first element contains only one atom simply just write the name of the atom so this is selenium hexa fluoride the last element ends in ide now here we have two nitrogen so we're going to say dinitrogen penta oxide or simply pentoxide now let's work backwards what is the formula for phosphorus trichloride and also try these as well what's the formula for carbon monoxide and silicon tetrachloride phosphorous trichloride so we have a p and we have a cl but we have three cl since we have the word try carbon monoxide so mono oxide that means we have one oxygen silicon tetrachloride tetra means four so we have four chlorine atoms so for molecular compounds it's not very difficult to name them or write the formula you simply need to know the names of the first 10 prefixes monodiotri all the way to deca before we move on to naming ionic compounds we need to go over the names of common monoatomic and polyatomic ions so for example clo4 this is a polyatomic ion it's an ion that contains many atoms poly means many this is called perchlorate cl o3 minus this is simply called chlorine perchlorate compared to chloride simply has one more oxygen clo2 minus is called chlorite eight usually has one more oxygen and i and clo minus is known as hypochlorite hypo means below or less so hypochlorite has one less oxygen and chloride cl minus is a monoatomic ion it's an ion composed of one atom monoatomic ions usually has the suffix eyed when you see that there's no oxygen attached to it when you hear the words eight and i typically that element has some number of oxygens attached to it so4 2 minus you need to know that this is called sulfate and what do you think so32 minus is called an s2 minus since so3 has one less oxygen than so4 if so4 sulfate so3 is sulfite s2 minus is a monoatomic ion so it's going to have the suffix ide so this is called sulfide what do you think the names for these ions are po4 three minus po3 three minus p3 minus hpo4 two minus and h2 po4 minus po4 3 minus is known as phosphate so if you know the first one you could find the rest po3 has one less oxygen so if po4 is phosphate po3 is phosphite p3 minus this is phosphide with the ide ended hpo42 minus this is hydrogen phosphate h2po4 minus is dihydrogen phosphate now there are some others you need to know co3 two minus this is known as carbonate so based on that what do you think hco3 minus is what's the name for this particular polyatomic ion hco3 minus is known as hydrogen carbonate or more commonly bicarbonate now what about oh minus c2h3o2 minus c2o2 minus and cn minus oh minus is known as hydroxide c2h3o2 minus this is called acetate c2 o2 2 minus this is oxalate and the last one cn minus is known as cyanide but now there's more what about c r o for two minus c r two o seven two minus m n o four minus o two minus o two two minus cro4 this is called chromate cr2o7 that's dichromate and the next one mno4 minus is permanganate if you see o2 minus where the individual oxygen has a charge of negative two this is called oxide but if you see o2 two minus where each oxygen atom has a charge of negative one so two of them has an overall charge of negative two this is known as peroxide and if you see o2 with a negative one charge meaning each individual oxygen atom has an oxidation state of negative one-half if you divide negative one by two this is known as superoxide so these are the different forms of oxide but the most common is just oxide peroxide you may see that occasionally superoxide is rare now let's go over naming compounds so let's say if we wish to name nacl which is an ionic compound it has a metal and a nominal so the first element simply write the name n a is called sodium now the second element think of the ion that is part of that compound this is cl minus which is called a chloride so the second element has the ide ending if it's a monoatomic ion so this is sodium chloride go ahead and name these elements mgo cas albr3 and let's see g-a-n and finally zn f2 so mgo mg is known as magnesium and oh the second part it's a monoatomic ion so it's going to be called oxide now what about cas ca is calcium and for the second element we need to add the ident so instead of saying sulfur we're going to say sulfide now what about albr3 al is aluminum and br instead of saying bromine it's bromide now what about the next one g-a-n ga is called gallium and n represents nitride so it's gallium nitride and the last one zn is zinc and instead of saying f fluorine for f it's going to be fluoride the u comes before the o don't put o u it's u o try these b a so4 let's see li clo3 k c n n a o h sr 3 po4 2 and mg no32 so now we have ionic compounds that contain polyatomic ions if you know the names of the polyatomic ions it's not going to be difficult so ba you need to know the name for ba ba is called barium and so4 is the sulfate ion so this is simply called barium sulfate so that's not too bad so let's try the next one li is lithium and clo3 as we mentioned before that is chlorine so we have lithium chlorine now what about the next one kcn so what is k k is potassium and cn is another polyatomic ion and this one is called cyanide very dangerous stuff now what about naoh na is sodium and the oh minus ion that's a polyatomic ion so that's hydroxide now what about the next one sr3po42 the first element is called strontium and the second one the polyatomic ion you simply need to know that it's phosphate so it's going to help you a lot for the rest of your chemistry course if you commit the polyatomic ions to memory because when you're working with math problems typically you need to know the formula of the compound so they may give you a name let's say barium sulfate you need to be able to write the formula calculate the molar mass but if you don't know what sulfate is you can't do the problem so it's going to put you at a serious disadvantage if you don't know the polyatomic ions especially for the rest of your chemistry course so to put it this way your grade significantly depends on knowing those polyatomic ions your teacher may give you the polyatomic ion sheet on the test but you'll be able to solve the problems faster if you simply know it now what about the last one here we have mg which is magnesium and no3 is nitrate so it's simply called magnesium nitrate now sometimes you may have compounds that have multiple oxidation states which are basically multiple charges and for such compounds you need to specify which charge it has one name in it and you would do that using the roman numeral system so let's go over the roman numeral system this number represents one this represents two we have two eyes this is three now if you see a v v represents five now if you see like an i to the left of the v it represents subtraction it's like five minus one so this represents four now if the i is to the right of the v it represents addition five plus one is six so this is five plus two which is seven and it's rare that you ever need to go past seven so we'll stop there now let's say if we have the formula cu cl2 and cucl so how would you name these two compounds cucl is copper one chloride cucl2 is copper ii chloride well you might be wondering well that's not bad all you need to do is look at the subscript well generally that's going to give you the answer it's not always the case so sometimes this will be the roman numeral but you can't always rely on it this number means that copper has a plus two charge now chlorine as chloride has a minus one charge and there's two of them so the net negative charge or the total negative charge is minus two and we only have one copper ion so that copper ion has to have a plus two charge to neutralize the two negative charges now for the one on the bottom we only have one chloride ion so this copper only needs a plus one charge to neutralize the negative one charge so because the copper is in a plus one oxidation state it's copper one chloride now it turns out there's another way you can calculate the oxidation state of copper and that is by using an equation copper plus two chlorine atoms has to have a net charge of zero notice that there's no overall charge and this compound is neutral if there was an overall charge you'll see like a negative two on the outside or something so we need to solve for the charge on copper so let's put let's replace copper with x and let's substitute negative one with chlorine or chlorine with negative one that's what i'm going to say so two times negative one is negative two to solve for x we need to add two to both sides so therefore x or copper has an oxidation state or a charge of plus two so that's how you can find it for the other example it's going to be c u plus c l which equals zero so c l is negative one if you add one to both sides you'll see that copper is equal to plus one so it's copper one chloride okay let's try fvs and fe2 s3 so for fes do you think it's rn1 sulfide since the subscript is 1 or is it something else so let's find the oxidation state of fe sulfur has a negative two charge so f e has to be or has to have a plus two charge since they're in a one to one ratio if you write the equation and if you replace s with negative two you'll see that f e has a plus two charge so therefore it's not iron one sulfide rather it's iron two sulfide so don't always rely on the subscripts it's a good indication of what it may be but always double check it so in this particular case is it iron three sulfide or is it something else let's find out now let's write an equation two f e plus three s has to add up to zero so s has a charge of negative two three times negative two is negative six and if we add 6 to both sides it's going to be 2fe which equals plus 6. so to solve for f we got to divide by 2. 6 divided by 2 is 3 so in this particular case f e does have a plus 3 oxidation state so in this case it is three so it's going to be iron three sulfide now let's try another example try these pbo and sno2 so even though lead and tin are not transition metals they do have multiple oxidation states typically plus two and plus four so you know that oxygen has a negative two charge that means pb has to have a plus two charge since these two are in the one-to-one ratio that means the charges are the same even though the sign is opposite so this is going to be called lead to oxide now the one on the bottom let's solve it so we have sn plus two oxygen atoms equals to a net charge of zero and each oxygen has a charge of negative two so two times negative two is negative 4. if we add 4 to both sides 10 is in the plus 4 oxidation state so this is going to be called 10 4 oxide so now let's talk about how to write the formula of an ionic compound so how would you write the formula for lithium chloride the first thing you should do is write the ion to lithium as an ion has a plus one charge it's an alkali metal it has one valence electron and elements in group 1a typically form ions with plus one charges chloride is a halogen it's going to have a minus one charge if the charges are the same you can simply write them in the one-to-one ratio so another example of this is calcium solenoid calcium is an alkaline earth metal with a plus two charge and selenium is a calcagen that's below sulfur and it has a minus two charge because the charges are the same you can simply write them in a one-to-one ratio another example is aluminum nitride aluminum is in group 3a of the periodic table so it has a plus 3 charge and nitride is a group 5a element and it has a minus 3 charge so here the charges are the same so you can simply write them as a outland so that's the first thing that you want to keep in mind now what about when the charges are different so let's say if we have magnesium bromide magnesium has a plus two charge it's an alkaline earth metal and bromide a halogen has a minus one charge so the charges are different so in this case you can use the crisscross method so this is going to be mg1br2 but if you have a one you don't really need to write the one so it's simply mgbr2 now what about aluminum sulfate aluminum has a plus three charge and sulfate this is where you need to know your polyatomic ions it's so4 two minus so using the crisscross method it's going to be a l 2 so4 3. now whenever you have multiple polyatomic ions you need to enclose it within a parenthesis what about this one sodium phosphate how would you write the formula for it sodium is an alkali metal with a plus one charge phosphate is a polyatomic ion which is po43 minus so using the same crisscross method it's going to be an a 3 po4 now we don't need to write the one so we can simply leave it as na3po4 now what about this one lead 4 sulfide feel free to pause the video and try this example so in this particular case the 4 tells us that lead has a plus 4 charge sulfur has a negative two charge typically and if we use the crisscross method it's going to be pb 2 s4 but notice that we have two even numbers and we don't have the lowest whole number ratio if you can divide it by a whole number you should so if we divide both numbers by 2 it's going to be pb1 s2 which we could simply write it as pb s2 so this is the case where the subscript is not always the charge as you can see we were able to reduce the subscripts and that's why these two don't match now the next thing that we need to go over is the nomenclature of acids whenever you see a hydrogen to the left of a non-metal it's an acid now there are some things that you need to know eight is associated with ick when writing the name of the acid i is associated with is and i'd will have the prefix hydro and the suffix ic and for all of these add the word acid so let me give you some examples well let's start with uh h2so4 so h2so4 contains the polyatomic ion sulfate so let's focus on the 8 part we know we need to replace it with ick so to write the name of the acid write the element first which is sulfur and then add the suffix egg and then add the word acid so this is called sulfuric acid not bad right now let's say if we want to name h2 so3 so notice that it contains the polyatomic ion sulfide so let's focus on the suffix i so we're going to have to replace it with this so let's write the element first sulfur and then let's add the is part to it and then the word acid so this is called sulfurous acid now what about h2s so s or s2 minus is a monoatomic ion and it's called sulfide so it has the ide suffix so before we write the element sulfur we need to put the prefix hydro and then let's write the element sulfur and then let's replace i'd with the suffix ic and then let's add the word acid so this is called hydrosulfuric acid now what about this one hclo4 how would you name this acid feel free to pause the video as you work out this example so the first thing we need to do is identify the polyatomic ion clo4 minus is known as per chlorine so all we need to do is replace the eight part with ick so this is going to be called perchloric and then add the word acid to it so perchloric acid now what about hclo what's the name for this acid so clo is the polyatomic ion hypo chloride so let's replace it with this so to name the acid it's simply going to be hypochlorous acid now what about hcl how can we name that acid so the anion cl minus is known as chloride because it has an ide ending we need to add the prefix hydro and then instead of saying chlorine after the r we're going to add ick so hydrochloric acid now we're going to work backwards if you're given the name how can you write the formula for example what is the formula for phosphoric acid so notice that we don't have the prefix hydro so that means that it's associated with a polyatomic ion we need to replace ick with a so this is associated with the phosphate polyatomic ion phosphate is po43 minus once you've identified the ion you simply need to add hydrogens to it because the charge is negative three we need to add three hydrogens to it so it's going to be h3 po4 so this is the formula for phosphoric acid let's try another one carbonic acid so we don't have the prefix hydro so it's associated with a polyatomic ion so let's replace ich with eight so we need to write the polyatomic ion carbonate carbonate is co3 two minus and since it has a negative two charge we've got to add two hydrogens to it so the name of carbonic acid or the formula for it is h2co3 now what about this one hydrobromic acid so because we have the prefix hydro and the suffix ick it's associated with ide or bromide and bromide is a monoatomic ion which is br minus because it has a negative one charge we only need to add one hydrogen to it so the formula for hydrobromic acid is simply hbr now what about iotic acid what's the formula for it so there's no hydro so it's a polyatomic ion that contains oxygen and if we replace the egg part with eight it's associated with the polyatomic ion iodine now chlorate was clo3 minus ioda is io3 minus the halogens they follow a similar trend so to write the formula for iodic acid because we have a negative one charge we only need to add one hydrogen so it's going to be hio3 now here's the last one acetic acid so if we replace egg with eight this is associated with acetate acetate is c2h3 o2 negative one so we need to add one hydrogen to it so the formula is hc hc2h3o2 so that's the formula for acetic acid now the next thing that we need to talk about in chemistry is grams moles atoms things like that now mass represents the quantity of matter and in chemistry mass is usually measured in grams one kilogram is a thousand grams now what about moles what is a mole the best way to understand what a mole is is to compare it with a dozen a dozen is simply a quantity a dozen represents 12. a dozen eggs is 12x a dozen calculators 12 calculators a dozen is to 12 the same way as a mole is to a very large number a number called avogadro's number which is 6.02 times 10 to the 23. so if you have a mole of pencils you have 6 times 10 to the 23 pencils if you have a mole of atoms you have 6 times 10 to the 23 atoms and so a mole is just a very large quantity now there's something called the molar mass molar mass is the ratio between the mass and the moles it's grams over moles and in the periodic table you'll see this number below carbon which is 12.01 the average atomic mass of carbon or you could simply say atomic mass this is also the molar mass of carbon and the units for molar mass is 12.01 grams per mole so as you can see molar mass is simply the mass divided by moles grams over moles now let's say if you wanted to calculate the molar mass for ch4 how would you do it all you need to do is add up the atomic masses for every atom in that molecule carbon has an atomic mass of 12.01 and for hydrogen it's about 1.008 but times 4 since we have 4 hydrogens so let's round it and let's say this is 12 and hydrogen is 1. so the molar mass of methane is about 16 grams per mole calculate the molar mass for sodium hydroxide and for glucose so the atomic mass for na is 23 for oxygen is 16. for hydrogen it's one so sodium hydroxide has a molar mass of 40 grams per mole so what this means is that one mole of sodium hydroxide has a mass of 40 grams so two moles of sodium hydroxide will have a mass of 80 grams so molar mass is simply the ratio between grams and moles now what about the molar mass of glucose c6h12o6 now what's the answer so the six carbon atoms each with an atomic mass of 12 there's 12 hydrogen atoms which has an atomic mass of one and six oxygen atoms each with an atomic mass of 16. six and twelve is seventy two and six times sixteen is ninety six seventy two and twelve that's eighty four and eighty four ninety six that's one eighty so the molar mass of glucose is 180 grams per mole so one mole of glucose has a mass of 180 grams two moles of glucose has a mass of 360 grams three moles of glucose has a mass of 540 grams and you can see a pattern there now the next thing we need to talk about is mass percent if you want to find the mass percent of an element in a compound is simply the mass of the element divided by the total mass times a hundred percent so for example let's say if we want to find the mass percent of carbon in methane so the atomic mass of carbon is 12. now the total atomic mass is the mass of carbon plus the mass of the four hydrogen atoms times 100 so it's 12 out of 16 times 100 and so you're going to get 75 percent carbon now if you want to find let's say the percent of hydrogen it's going to be the mass of hydrogen or the molar mass of hydrogen divided by the total mass 4 out of 16 times 100 is 25 so it's 25 hydrogen 75 carbon notice that the total percentage is 100 so now it's your turn calculate the percent by mass of sodium in sodium hydroxide so we know the molecular mass or the atomic mass of sodium is 23. the formula mass of the naoh formula unit we calculated that already it was 23 plus 16 plus one which is 40. so at this point if you type it in 23 over 40 times 100 you should get a mass percent of 57.5 so that's the percent of sodium in this compound now how much or what is the percent of hydrogen and sodium hydroxide so the mass of hydrogen is one divided by a total molar mass of 40. so it's 1 out of 40 times 100 so it's 2.5 percent by mass for hydrogen now what about for oxygen since oxygen is the last element we could simply do 100 minus 57.5 minus 2.5 or 100 minus 60. so that means that it's 40 percent oxygen because the three percentages they have to add up to 100 so if you typed in 16 out of 40 times 100 you should get 40 for the sake of practice let's try another example let's use glucose find the mass percent of carbon in this compound so the mass of carbon there's six carbon atoms so six times twelve that's the total molar mass of all the carbon atoms in glucose now the total molar mass for all of the atoms in glucose is 6 times 12 plus 12 plus 6 times 16 times 100 so the six carbon atoms has a molar mass of 72 the molar mass of the entire compound is 180. and so now we just got to type these numbers in the calculator and so it's 40 percent by mass for carbon so now you know how to find the mass percent of an element within a compound now the next thing that we need to talk about is converting grams into moles so for example let's say if you have 48 grams of carbon how many moles of carbon is this equivalent to so whenever you want to convert from grams to moles or moles to grams you need the molar mass based on the periodic table the molar mass of carbon is 12. so what that means is that one mole of carbon has a mass of 12 grams so let's convert start with what you have now since we have grams of carbon on the upper left side we need to put grams of carbon on the bottom so 12 is associated with it and so one mole of carbon is going to go on top so that these units cancel so it's simply 48 over 12 which is equivalent to four moles of carbon now let's make sense of it so the molar mass is 12. and as you mentioned before one mole of carbon is equal to 12 grams so two moles of carbon is equal to 24 grams three moles of carbon is equal to 36 grams so for every mole of carbon that you add the mass increases by 12. so 4 moles of carbon equates to 48 grams of carbon which is the answer that we wanted now try this example so let's say if you have 22 grams of carbon dioxide go ahead and convert it to moles of co2 so the first thing you need to do is find the molar mass of co2 the atomic mass of carbon is 12 and for oxygen is 16 but there's two of them so 16 times 2 is 32 plus 12 that's 44. so the molar mass is 44 grams per mole so now let's start with what we're given and we need to put grams on the bottom so there's 44 grams of co2 per one mole of co2 so whenever you need to convert from grams to moles take the mass in grams and simply divide it by the molar mass so 22 divided by 44 is 0.5 so we have 0.5 moles of co2 now if you need to go the other way let's say if you want to convert from moles to grams you need to multiply the moles by the molar mass so let's say if we have three moles of neon let's convert it to grams of neon so let's start with what we're given now if you use the periodic table if you take a look at it you'll see that the atomic mass of neon is approximately i'm gonna round it it's about 20 grams per mole so there's 20 grams of neon per one mole of neon so you want to set it up in such a way that the unit moles of neon cancels and so since we have two numbers on top we got to multiply 3 times 20 is 60 so you're going to get 60 grams of neon try this one let's say if you have five moles of c2h6 molecules convert this into grams of c2h6 c2h6 is ethane so let's find the molar mass first so we have two carbons each with an atomic mass of 12 and six hydrogens each with a atomic mass of one so 2 and 12 is 24 plus 6 is 30. so it's 30 grams per mole so let's start with five moles of ethane let's convert it to grams so there's 30 grams of ethane per one mole of ethane therefore the unit moles of ethane will cancel and so it's 5 times 30 we know 5 times 3 is 15 so 5 times 30 is 150 you got to add the zero so we have 150 grams of ethane so that's how you can convert from molster grams using the molar mass so if you want to write an equation the moles is equal to well let's actually write it this way mass in grams is equal to the molar mass times the moles so let's use lowercase m for mass and let's use capital m for molar mass and n for moles be careful though capital m sometimes could be molarity so watch out for that so mass is molar mass times moles now let's say if you have three moles of carbon atoms how can we convert that to the number of carbon atoms so we have three moles of carbon how many atoms do we have so to answer this question we need to use avogadro's number one mole is equal to six times ten to the twenty-three it's really six point zero two two times ten to the 23 but i'm going to round it to six times ten to the 23. so let's start with three moles of carbon one mole of carbon is equal to six times 10 to the 23 atoms of carbon so that's how you can convert from moles to atoms simply multiply by avogadro's number so the answer is 6 times 3 that's 18 so it's 18 times 10 to the 23 atoms now to put it in proper scientific notation we need a number between 1 and 10 18 is greater than 10 so let's move the decimal one unit to the left any time you move the decimal one unit to left the exponent needs to go up by one so you have to add one to 23. so it's 1.8 times 10 to the 24 atoms of carbon now let's say if we have four moles of methane how many molecules of methane do we have and how many atoms of hydrogen do we have so let's find molecules of methane so methane is not an atom you can't go directly from four moles of ch4 to atoms because this is a molecule a molecule is a particle that is composed of many atoms so when using avogadro's number one mole of methane corresponds to 6 times 10 to the 23 not atoms of methane but molecules of methane since ch4 is a molecule so if we simply multiply 4 by 6 times 10 to the 23 that's all we need to do to get the molecules of ch4 so that's going to be 24 times 10 to the 23 which is the same as 2.4 times 10 to the 24 molecules of ch4 now if we want to find the atoms of hydrogen we'll need to take it one step further in one molecule of ch4 you need to realize that there's four atoms of hydrogen because of the subscript four so four times six is 24 24 times 4 if 20 times 4 is 80 4 times 4 is 16 80 and 16 is 96 so 24 times 4 is 96 so it's 96 times 10 to the 23 atoms of hydrogen which is the same as 9.6 times 10 to the 24 atoms so this is the answer so that's how you can go from moles to molecules to atoms now sometimes you may need to convert from grams to atoms so let's say if you have 16 grams of helium convert it to atoms of helium now helium is not a molecule it's made up of atoms so we don't need that extra step to go from molecules to atoms but first before we can go to atoms we need to convert grams to moles and then most atoms you can't go directly from grams to atoms so to go from grams to moles we need the molar mass the atomic mass or molar mass of helium is about four it's four grams per mole so four grams of helium equates to one mole of helium so these units cancel and now we can convert moles to atoms one mole of helium is six times 10 to the 23 atoms of helium so it's going to be 16 divided by 4 which is 4 4 times 6 is 24 so 24 times 10 to the 23rd is 2.4 times 10 to the 24th atoms of helium now let's say if you have three times 10 to the 23 atoms of argon and let's say you want to convert that to grams of argon try that example so first we need to convert atoms into moles and we can use avogadro's number so one mole of argon atoms is equal to 6 times 10 to the 23 atoms so the unit atoms cancel and now we can go for moles of grams the molar mass for argon is about 40. so there's 40 grams of argon for every mole of argon so those units disappear so now let's do the math we can cancel the ten to the twenty thirds because they're the same three divided by six is a half and half of 40 is 20. so the answer is 20 grams of argon so now you know how to convert from atoms to grams now let's switch gears and go to uh reactions you need to be able to classify the different types of reactions and you need to know how to balance it so let's start with combustion reactions so let's say if you have propane which is c3h8 and we're going to react it with oxygen gas if you see carbon hydrogen and oxygen this is going to be a combustion reaction the products of a combustion reaction are typically co2 and water now to balance a reaction your goal is to make sure that the atoms on the left side and on the right side are the same and to make it equal you can modify the coefficients of the reaction the coefficients are the numbers in front of these substances the subscripts are the small numbers like the 3 the 8 the 2 those are the subscripts you can't change those when balancing the equation you can only change it when writing the formula but when you're balancing an equation you can only add subscripts i mean not subscripts but coefficients which are the number in front of these molecules when balanced in a combustion reaction the first thing that you want to do is balance the carbon atoms so we have three carbon atoms on the left therefore we got to put a three in front of co2 now the next thing you want to move to is the hydrogen atoms we have eight on the left two on the right eight divided by two is four so let's put a four in front of h2o now you wanna save the oxygen atoms for last so three times two is six so we have six oxygen atoms in the three co2 molecules four times this invisible one is four so we have four oxygen atoms in the four water molecules six and four is ten so we have a total of ten oxygen atoms on the right side so what number do we need to put in front of o2 to balance it well 10 divided by the subscript 2 is 5 so we need a 5 in front of o2 and since we don't need a number here we could put a 1 and now the reaction is balanced we have three carbon atoms on both sides 10 oxygen atoms and eight hydrogen atoms on both sides so that's how you can balance a combustion reaction now let's try another example c2h5oh which is known as ethanol plus o2 produces carbon dioxide and water go ahead and balance this particular combustion reaction so notice that we have two carbon atoms on the left side we need to put a two in front of water and we have a total of six hydrogen atoms five plus one is six six divided by two is three so we need to put a three in front of h2o to notice that we have four oxygen atoms from the two co2 molecules and three oxygen atoms from the three water molecules four plus three is seven now notice that we already have an oxygen atom in ethanol so what number do we need to put in front of o2 since we already have one oxygen atom on the left side in ethanol we need six oxygen atoms from the o2 molecule because one plus six is seven so six divided by the two is three therefore we need to put a three in front of o2 so notice that we have a total of seven oxygen atoms on both sides so we have four and three which is seven one and three times two which is six so six and one is seven so everything is balanced we have two carbon atoms on both sides six hydrogen atoms and seven oxygen atoms by the way are combustion reactions considered to be redox reactions what would you say consider this reaction butane plus oxygen produces co2 and water here's another combustion reaction it turns out that every combustion reaction is a redox reaction a redox reaction is simply a reaction where electrons are being transferred from one element to another a quick way to determine if a reaction is a redox reaction is to look at the substances in the reaction on the left side we have the reactants on the right side you have the products if you see a pure element on one side of the reaction and that element in the compound then it's a redox reaction so here we have a pure element and here's a compound if you see that it's definitely going to be redox now how would you balance this combustion slash redox reaction so let's start with the carbon atom so we have 4 on the left so we need to put a 4 in front of co2 now we have 10 hydrogens on the left side 10 divided by 2 is five so we need to put five in front of h2o now how many oxygen atoms do we have on the right side so we have eight and five which is thirteen thirteen divided by two is thirteen over two so notice that we have a fraction whenever you get a situation like this simply multiply everything by two so it's going to be two c four c4h10 now 13 over 2 times 2 the twos cancels and you're just going to get 13. so it's going to be 1302 and then 8 co2 plus 10 h2o so notice that the reaction is now balanced we have a total of eight carbon atoms 20 hydrogen atoms 10 times 2 is 20 and 26 oxygen atoms 8 and 2 is 16 plus the 10 from water that adds up to 26 so everything is balanced in this particular reaction here's the reaction for you when zinc is mixed with elemental bromine what's going to happen what product will be produced this is a combination reaction if you mix a and b and you get a single product that's known as a combination reaction every combination reactions are redox reactions some are some are not now if you mix a metal and a non-metal these two would react in such a way to produce an ionic compound zinc is going to give up its electrons and it's going to turn into the zinc plus 2 cation bromine is going to acquire the electrons and it's going to turn into bromide to write the formula of the product simply use the crisscross method so it's going to be zn1 br2 which we're simply going to write znbr2 and the reaction is already balanced so is this reaction a redox reaction notice that we have zinc as a pure element and zinc within a compound so when you see that a pure element on the left compound on the right or vice versa it's a redox reaction now which substance is oxidized and which substance is reduced so you need to look at something called oxidation states the oxidation state of any pure element is always zero now in zinc bromide we know that zinc has a plus two charge elemental bromine has an oxidation state of zero but bromide in zinc bromide individually has an oxidation state of negative one because bromide typically forms a negative one charge whenever the oxidation state increases the substance is oxidized so the oxidation state of zinc went from zero to plus two so zinc was oxidized the substance that is oxidized is always a reactant never the product so it's always on the left side now bromine was reduced notice that the oxidation state decreased or was reduced from zero to negative one so br2 was reduced the substance that is oxidized is known as the reducing agent and the substance that is reduced is the oxidizing agent zinc is the reducing agent because it caused the other substance bromine to be reduced bromine is the oxidizing agent because it caused the other step since zinc to be oxidized metals most metals particularly the active ones are usually good reducing agents because they like to give away electrons now metals like bromine are oxidizing agents because they like to take away electrons whenever a substance gives away or loses electrons it is oxidized a substance that receives or gain electrons is said to be reduced now let's say if we were to mix calcium oxide and water calcium oxide is a basic anhydride metal oxides are considered basic anhydrides because when you add them to water they turn into a base calcium oxide reacts with water to produce calcium hydroxide whenever you see a metal with an oh it's a base basis produces hydroxy ions in solution so notice that this is a combination reaction it's in the form a plus b turns into a b now this particular combination reaction which is already balanced is it a redox reaction or is it not notice that there's no pure elements in this reaction we have a compound compound compound if you don't see a pure element it's safe to say this is not a redox reaction so there's no transfer of electrons in this reaction now let's say if you were to have calcium carbonate and if you add heat to it metal carbonates they decompose when you add heat this is going to turn into calcium oxide and it's going to release a volatile component that is contained in calcium carbonate that volatile component is carbon dioxide gas whenever you add heat if a gas can escape it will escape now what kind of reaction do we have here so we have the reverse of a combination reaction we have a larger product breaking down into two smaller components so this is known as decomposition now is it redox or is it not a redox reaction notice that we have a compound compound compound no pure elements so it's not a redox reaction now let's say if we have magnesium nitride which is a solid if we add heat to it what's gonna happen typically whenever you add heat to a compound if it's enough if it's like a lot of heat it can decompose if there's a gas that can be produced then the formation of the gas is going to drive the reactions to the right making it spontaneous when you heat magnesium nitride it's going to turn into magnesium metal and nitrogen gas nitrogen gas is very stable so heat is going to drive the reaction to the right producing this volatile gas to balance it we simply need to put a 3 in front of mg so is this a redox reaction or is it not so we know this is a decomposition reaction we have a compound breaking into its elements and it turns out it is a redox reaction here we have a compound and here we have a pure element so it's a redox reaction now there are some other common decomposition reactions that you should know the decomposition of potassium per chlorine if you add heat to it this breaks down into potassium chloride and oxygen another one is mercury oxide which is a solid if you add heat it's going to turn into mercury metal which is a liquid and you're going to get oxygen gas so notice that heat favors the formation of a gas if the gas can be formed it's going to drive the reaction to the right making it spontaneous so both of these are decomposition reactions now are they redox reactions if you look at the first one we have a compound and here we have a pure element so it's a redox reaction for the second one compound pure element redox to balance the first one notice that we have three oxygens on the left two on the right the least common multiple of two and three is six so to make them equal we need to get six oxygen atoms on both sides so we need to put a two in front of kcl3 and a 3 in front of o2 so we have 6 oxygen atoms on both sides notice that we have 2 potassium atoms so we've got to put a 2 in front of kcl now it's balanced for mercury oxide all we got to do is put a 2 and a 2 and it's balanced so we have two mercury atoms and two oxygen atoms now we said that whenever you have a metal oxide with water it's going to produce a base so metal oxides are basic anhydrites now what about non-metal oxides like sulfur dioxide non-metal oxides are acid anhydrides because when you put them in water they will turn into an acid so2 plus water turns into h2so3 if you put sulfur trioxide in water it's going to turn into sulfuric acid if you mix carbon dioxide with water it turns into carbonic acid so as you can see non-metal oxides are acid and hydrides metal oxides are basic anhydrites now let's say if you have calcium hydroxide if you add heat you're going to get the reverse reaction of what we had in the last example this is going to break down into calcium oxide and water now depending on the temperature water can escape as a liquid or if it's hot enough it can leave our steam now let's say if you have a single replacement reaction zinc plus actually let's change it let's make it aluminum plus hydrochloric acid what are the products of a single replacement reaction aluminum is going to displace hydrogen out of the solution and it's going to pair up with cl aluminum is going to lose its three electrons turning into the aluminum plus three ion and chloride usually has a minus one charge so using the crisscross method when these two get together they turn into al cl3 now when hydrogen is displaced out of the solution it's going to be elemental hydrogen which is diatomic and it's going to leave as gas aluminum is a solid hcl is aqueous which means that it's dissolving water aluminum chloride will also be an aqueous phase so in this reaction we're placing a solid chunk of aluminum in a solution of hcl which means the hcl is mixed with water so whenever you see aq that means that it's dissolved in water now this single replacement reaction is it a redox reaction it turns out that all single replacement reactions are redox reactions notice that we have a pure element and a compound so it's a redox reaction now which substance is oxidized and which one is reduced so aluminum is in the zero oxidation state because it's a pure element but in its compound is plus three now hydrogen is in the plus one oxidation state because chlorine is minus one whenever hydrogen is bonded to a non-metal it usually has a plus one charge but when it's bonded to a metal it usually has a minus one oxidation state or charge now elemental hydrogen is zero so aluminum goes from zero to three so the oxidation state goes up so aluminum was oxidized now hydrogen in hcl it went down or it was reduced from one to zero so hcl was reduced since aluminum was oxidized aluminum is also known as the reducing agent hydrogen was reduced so it's called the oxidizing agent so as we can see here most active metals are reduced in agents and non-metals are usually oxidizing agents going back to this reaction a quick way to distinguish a single replacement reaction from let's say a double replacement reaction is this method in a single replacement reaction typically you have an element reacting with a compound when you see that it's usually a single replacement reaction by the way how would you balance this reaction what would you do to balance it so notice that we have three chlorine atoms so we're probably gonna have to put a three in front of hcl but notice that we have an odd number of hydrogens and an even number over here the least common multiple between three and two is six so that tells us that we need six hydrogen atoms so let's put a three here to make it six and let's put a six there and let's rebalance it so now that we have six hydrogen atoms on both sides let's balance the chlorine atoms we have six on the left three on the right so we need to put a two in front of alcl3 and so since we have two aluminum atoms on the right side we got to put a two in front of ao now the reaction is balanced now consider this reaction let's say if we have an aqueous solution of silver nitrate plus magnesium chloride and we want to find out what the products for this reaction will be nitrates are always soluble so this is going to be aqueous to know this you need to understand the solubility rules nitrates acetates ammonium which is nh4 plus are always soluble alkali metals like lithium sodium potassium rubidium they're always soluble the halides like chloride bromide iodide are generally soluble except with silver lead and mercury so with magnesium chloride is soluble now this is a double replacement reaction we have a compound reaction with a compound in a single replacement reaction it's an element plus a compound in a double replacement reaction the two groups on the outside are going to pair up together and the two on the middle are going to pair up so ag is going to pair up with cl so we have a g1 and cl minus one because these two have the same charge even though the sign is opposite we can write them in a one to one ratio now chloride is soluble with everything except silver lead and mercury so silver is an exception so this is a solid whenever you mix two aqueous solutions together and if you get a solid product this double replacement reaction is also known as a precipitation reaction which is what we have in this particular case now we need to find the other product so let's pair up magnesium with nitrate magnesium is an alkaline earth metal with a plus two charge and nitrate is a polyatomic ion with a minus one charge using the crisscross method we could see that it's mg1 no32 whenever you have multiple polyatomic ions make sure you enclose the polyatomic ion within the parenthesis now we said nitrates are always soluble so magnesium nitrate is going to be aqueous so now what we need to do at this point is balance the reaction so we have two nitrates on the right side so we've got to put a 2 in front of h geno3 and we have two chlorines on the left side so we need a two in front of hcl and now the reaction is balanced now this particular double replacement reaction would you consider it a redox reaction what would you say notice that there's no pure element in this compound i mean not compound but there's no pure element in this reaction this is a compound that's a compound compound compound so double replacement reactions are never redox reactions because you won't see any pure elements in this reaction now typically with double replacement reactions you need to be able to write the net ionic equation how can we do that in this particular example the first thing that you need to do is write the total ionic equation so everything that is in the aqueous phase we need to separate it into ions except the solid so we have two ag plus ions and two nitrate ions in agno3 and this compound mgcl2 we have a magnesium ion and two chloride ions agcl is a solid so we're gonna leave it that way everything that we separate into ions all of these are in the aqueous phase by the way and then magnesium nitrate we could separate that into mg plus two or mg two plus and two nitrate ions if you're submitting this into an online assignment typically instead of writing plus two you may have to write two plus now this is the total ionic equation our next step is to eliminate the spectator ions the spectral ions are those that do not participate in the reaction they just spectate they watch so on the reaction they look exactly the same the nitrate ions are spectrons we can cancel them out and magnesium is expected on so what remains is the net ionic equation which is 2a g plus plus 2cl minus produces two agcl notice that each of these has a coefficient of two which means we could divide each one by two so it simplifies to this a g plus which is in the aqueous phase and cl minus which is also in the aqueous phase these two will react to produce solid silver chloride so this is the net ionic equation for this example now let's try another double replacement reaction what's going to happen if we make sodium hydroxide with sulfuric acid so this is an acid-base neutralization reaction when you mix a strong base with a strong acid they will react to produce salt and water but it's still a double replacement reaction which means it's not a redox reaction so the two on the outside will pair up sodium has a plus one charge and sulfate has a negative two charge which is important for you to know the polyatomic ion list because without that you won't be able to write the correct formula for sulfate if you don't know the right charge and you won't be able to write the net equation so you have to make sure you know your polyatomic ions so if we pair these two ions together it's going to be na2 so4 1 or just so4 so that's one of the products that we have to find the other product whenever you pair h with oh these two will just create water this is something that you should just know or commit to memory so now we have a balance reaction well we just have a reaction but we got to balance it so notice that we have two sodium atoms on the right side so we got to put a 2 in front of naoh now to balance acid-base reactions here's what you can do to quickly get the answer notice that you have two hydroxide ions two h plus ions that's going to produce two water molecules it's always going to work out that way so this is a one so now the reaction is balanced so before we can write the net ionic equation we need to write the phases of every substance so typically the stuff on the left for a double replacement reaction is usually an aqueous phase sodium hydroxide is soluble in water na is an alkali metal alkali metals are always soluble now acids for the most part are soluble in water i've never seen an acid that doesn't dissolve in water and what is a liquid so to write the total ionic equation everything that's in the aqueous phase we need to separate it into ions so we're going to have two na plus ions from naoh and two hydroxide ions now in the next compound sulfuric acid we have two h plus ions and one sulfate ion and sodium sulfate there are two sodium ions and a sulfate ion and water is a liquid so it's not aqueous therefore we need to leave it the way it is so what are these spectator ions in this total ionic equation so which ions look exactly the same on both sides so that's sodium and so now we can write the net ionic equation but notice that we have two hydroxides two h plus two water molecules so every coefficient is two let's divide the coefficients by two so it's going to be one hydroxide which is the aqueous phase plus one h plus ion or hydrogen ion in the aqueous phase and this is going to produce liquid water so this is the net ionic equation for this acid-base neutralization reaction so that is it for this video by the way look out for my other videos on youtube particularly the ones on stoichiometry i've created one that's entitled stoichiometry grams moles atoms molecules it also has examples on limiting and excess reactants percent yield theoretical yield things like that and i've created another one on solution stoichiometry where it goes over molarity calculations and how to convert from grams to moles to molarity to liters and things like that and how to do dilution problems using the m1v1 equals m2v2 equations so take a look at those videos when you get a chance it continues from where we left off and that's all i got for today so thanks for watching i hope you found this video to be educational and have a great day