Transcript for:
Fundamentals of Chemistry for Beginners

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 of their properties so in the First Column you have H which represents hydrogen and then lithium sodium pottassium rubidium now hydrogen is a nonmetal but the other ones below that lithium sodium potassium rubidium and even cesium those are known as alkaline metals the alkaline metals are the most reactive of the metals in a periodic table if you let's say put sodium and 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 burum 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 1 a The Alkali earth metals is group 2A the rows are the period this is period one period 2 period 3 and so forth and next to potassium and calcium you have the transition metals you have have a scandium titanium vadium chromium manganese iron Cobalt nickel copper and zinc below copper you have silver and gold below zinc you have a cadmium and Mercury Mercury is HG next to Sil silver you have padium 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 plus2 OR plus three oxidation state copper is typically + one or plus2 so they have variable charges but some of the transition metals like zinc have a a common charge of plus two 99% of the time zinc has a charge of plus two same is true for cadmium silver is usually + one gold could be plus one or plus three Mercury could be+ one or plus2 so you need to know the charges of some of these ions Cobalt is usually between plus2 and plus three meanes could vary from plus2 to plus 7 chromium typically as a a monoatomic ion plus 2 and plus three so those are the transition medals 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 aines and then you have the elements on this side which we're about to go over so groups 1 to 2 a and groups 13 to 18 these are known as representative elements group 3 to 12 is the transition medals and then this is the inner transition metals which are nonrepresentative 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 andium next to Boron you have carbon and below that silicon germanium tin and lead this is group 4 a the group 3A 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 gum but gum I've seen the plus one and plus three state for indium it can be+ one or plus three and the same is true for theum but aluminum usually doesn't form the plus1 ion it's for the most part plus three now for the group four elements silicon for example can have a plus two or plus4 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 plus4 charge next we have nitrogen phosphorus selenium I mean not selenium I take that back below phosphorus is arsenic s SP 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 five veence electrons however they like to form a negative three charges these are the nonmetals at least most of them are nitrogen likes to form a minus three charge and the same is true for phosphide or phosphorus as an element it's called phosphorus but when it has a neg3 charge it's called phosphide n as an element is called nitrogen but as an ion with a neg3 charge is called nitride with the ID ending the next group group 6A or group 16 these elements they have six veence electrons and they like to form ions with a negative2 charge negatively charged ions are known as anions so we have oxygen sulfur selenium tonium and polonium these are known as the calogen next to that you have the group 7A element or group 17 and you have Florine chlorine bromine iodine or iodine and atine so these have seven veence 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 negative2 charge is 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 nonmetals like Helens are very very reactive Florine 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 Florine really wants to have electrons it is Electro negative electr negativity increases towards floring so as you go up and as you go to the right electro negativity increases so what this means is that Florine has a very strong desire for electrons florine's desire for electrons is greater than that of oxygen and chlorine so nonmetals tend to be Electro negative metals are usually electropositive Electro negative elements once they acquire the electrons that they want they form negative charges electropositive 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 it ask you which element is non-reactive carbon nitrogen Florine or neon your answer is neon now let's see if you get a question that asks you which of the following elements is is or shares the same chemical reactivity or is most similar chemically speaking let's say we have nitrogen oxygen sulfur Florine 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 calcin they're in the same column so Florine and chlorine are chemically similar to each other they're both Helens they have the same number of veence electrons and so their chemical reactivity is similar now you need to know where the metals and the non-metals 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 nonmetals so elements Like Oxygen Florine sulfur chlorine these are all non-metals but 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 geranium those are the most common metalloids that you'll be tested on Metals conduct electricity metals can also conduct heat as well metals are IM malleable they could be hammered into sheets and they're ductile they can be drawn into wires nonmetals do not conduct electricity metalloids they conduct a small amount of electricity nonmetals 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 metaloid do you think conducts more electricity silicon or geranium 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 geranium so carbon for the most part is considered to be a nonmetal silicon and geranium or metalloids tin think of a tin can tin metal well tin is a metal lead is 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 geranium so geranium even though it's a metaloid can conduct electricity better than silicon because geranium has more metallic character than silicon now now carbon has different forms known as allotropes carbon has carbon can be in a 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 penciled carbon graphite does conduct electricity so make sure you're aware of that so the metalloids are silicon geranium arsenic antimony te ban for the most part is considered to be a metaloid but the most common are silicon and geranium 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 and nitrogen is datomic then you have oxygen Florine 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 Florine is a gas chlorine is like a 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 Cove valent bonds and ionic bonds so what exactly is an ionic bond and what is the difference between a calent 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 veence electrons now as we mentioned before metals they like to give away their electrons nonmetals like to acquire electrons so sodium is going to give away its one electron to chlorine when 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 will like charges repel but opposite charge is 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 electr static 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 calent bond the electrons are shared for example let's say if we have two hydrogen atoms each with one veence 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 calent bond since we have sharing of electrons now because the elements are identical because they have the same electro negativity this is classified as a non-polar calent Bond because the electrons are distributed equally it's non-polar now let's say if we have two dissimilar elements for example hydrogen and Florine now these are both nonmetals two nonmetals typically form a calent bond now hydrogen is going to donate one electron to form the bond and Florine is going to donate one so HF looks like this now Florine is significantly much more electronegative than hydrogen so Florine is going to pull the electrons toward itself so because the electrons are shared unequally the bond is going to be considered a polar coent bond as Florine 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 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 Electro negative atom the electr negativity of Florine if you look it up in the table most textbooks would say 4.0 and for hydrogen 2.1 whenever the electro negativity difference if it's greater than than .5 or if it's equal to or greater than5 the bond is considered to be polar if it's less than 0.5 it's usually non-polar 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 non-polar carbon has an electr negativity value of 2.5 and for hydrogen it's 2.1 now both of these elements are non-metals so we have a CO valent Bond we just need to decide if it's polar or non-polar the difference is 2.5 minus 2.1 so it's about 04 therefore this bond is considered to be relatively non-polar since the difference is not 0 five 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 coent feel free to pause the video as you work out these examples so MGO magnesium oxide is it ionic or calent magnesium is a metal it's found on the left side of the periodic table oxygen is a nonmetal whenever you have a metal and a nonmetal combined this is going to be ionic CO2 carbon dioxide carbon is a nonmetal oxygen is a nonmetal when you have two non-metals you have a coent molecule if it's coent typically it's usually molecular so you can also classify as a molecular compound it's composed of molecules now what about water hydrogen is a nonmetal oxygen is a non-metal so this is classified as coent for lithium chloride lithium is on the left side of the periodic table and that's a metal chlorine is a nonmetal be careful cuz 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 a nonmetal so this is ionic Florine is composed only of non-metals so this is coent now because Florine it's made up of the same element the bond between those two elements is a non-polar calent Bond because thean difference is zero now the bond between carbon and oxygen that's a polar equalent bond because thean difference is much greater than 05 and between oxygen and hydrogen that's also a polar coent bond now you need to be careful with the exceptions for example 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 Justus 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 non-metals now within the sulfate ion you have coent bonds the bond between oxygen and sulfur is coent sulfur is a nonmetal oxygen is a nonmetal both of these elements are found in the upper right corner of the periodic table so that's a calent bond between the oxygen and the sulfur so if you have a compound that contains a metal and a non-metal 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 coent bonds now there are some ionic bonds that don't have Metals a good example is the ammonium ion if you see nh4 of something like ammonium chloride this is ionic the nh4+ 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 non-metals so this is a coent bond so ammonium chloride has ionic and calent 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 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 6 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 means the four electrons that are remaining so carbon has a total of six electrons notice that carbon is in group 4 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 and atomic number of two in this form it looks like the atomic number and the mass number are 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 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 a cental 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 cbal force which is caused by the electrostatic force between electrons and the protons a cental 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 centri force I know we kind of jump into physics here but it's a good time to talk about it now if opposite charges attract each other then life 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's 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 we have an element of Florine Florine has an atomic mass of 19 and an atomic number of nine how many protons neutrons and electrons are in this Florine 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 Florine has nine protons the mass number is 19 but the difference gives you the number of neutrons 19 - 9 is 10 so Florine 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 9us Z therefore there are nine electrons in this atom now out of the nine electrons how many electrons are valence electrons Florine has seven veence electrons you can find this number based on the group that Florine is located in Florine is located in group 7A which is the same as Group 17 and so it has seven veence electrons so how many core electrons does it have the total must be nine so 9 - 7 is 2 so Florine has two core electrons but seven veence 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 - 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 veence electrons does Arsenic have so arsenic is found in group 5A of the periodic table so therefore arsenic has five valence electrons so how many core electrons does it have so 33 - 5 is 28 therefore arenic has 28 core electrons so the core electrons plus the veence 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 three 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 - 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 - 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 -10 from the 10 electrons 13 - 10 is + three 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 - 15 is 16 so it has 16 neutrons to calculate the electrons is the atomic number minus the charge 15-3 is the same as 15 + 3 which is 18 electrons so if you add up the charges we have a net charge of posi 15 from the 15 protons and a net charge of8 from the 18 electrons so the overall charge 15 +8 is -3 so whenever an ion has more electrons than protons it has a net negative charge if it has more protons than electrons then the over all 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 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 - 6 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 their 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. 0 1 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 1% 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 th000 carbon atoms 990 would be carbon 12 10 would be carbon3 since 1% of a th000 is 10 you can calculate the average atomic mass by using a weighted average the average atomic mass is equal to the mass of the io times its relative percent abundance plus the mass of the other I tote 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 99 to convert percent to a decimal divide it 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 01 so if you multiply 12 by .99 you're going to get 11.88 if you multiply 13 by 01 it's going to be3 and if you add3 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 five on the periodic table now boron has two principal Isotopes Boron t 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 born atoms is the B10 isope and what percentage is the b11 io 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 ice toope is 70% that means that 30% is Bor on 11 so if x corresponds to 70 then 30 must be 1 - x because 1 -30 I mean 1 - 70 is30 so notice that x + 1 - x adds up to 1 and one represents 100% M2 is the mass of the second iope which is 11 and as you mentioned the percentage is going to be 1 - x so we need to solve for the value of x so it's going to be 10 x and if we distribute the 11 11 * 1 is 11 and 11 * X that's -1x so now we need to add like terms so the two like terms are 10 x and 11x 10 - 11 is1 or simplyx and now at this point we need to subtract both sides by 11 and now let's make some space 10.81 - 11 is119 those two numbers cancel so19 is X if you multiply both sides by1 X is9 which corresponds to 19% now X was associated with the B10 ice ta so we have 19% of boron 10 100 - 19 is 81% so that is the relative percent abundance of the other iceo b11 so notice that we have more of the b11 iob 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 Bor 11 ice to so this is how you can calculate the relative percent abundance of an ice taup um within an element what we're going to do now 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 3 and 12 now which are the following elements is the most reactive metal listed here the most reactive metal is typically an alkaline metal and lithium is the only alkaline metal in this group lithium is found in the First Column of the periodic table now which one is a nonmetal which element is found in the upper right corner of the prct table this is bromine bromine is a nonmetal 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 of the following elements has three veence electrons is it Fe mg G bromine aluminum or lithium it turns out aluminum which is found in group 3A or group 13 has three valance electrons consider these elements zinc bromine silicon iodine and Florine now these are datomic which of the following elements is a liquid at room temperature is it zinc bromine silicon iodine or Florine bromine is a red liquid now which of 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 metaloid silicon is a metaloid 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 Florine 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 of 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 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 Color 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 it to can form a variety of colors but chromium takes its one 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 Germania which of the following elements is a liquid at room temperature Mercury is liquid at room temperature it's called Quicks silver 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 padium Silver Platinum these elements are known as Noble Metals they're very stable chemically speaking they're very resist 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 geranium the only one that doesn't conduct electricity is the non-metal 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 metaloid 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 at room 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 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 it's made up of molecules a molecule is composed of two or more atoms it 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 ify 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 non-metal 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 ID 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 them 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 non-metal so it's ionic and it's a compound so it's a ionic compound anytime you of a compound it's never going to be a Pure Element zinc is composed of atoms but these atoms are coal bonded to each other and zinc is a Pure Element we only have one type of element in a substance Florine is a Pure Element but it's also a molecule because it's composed of it's a 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 a compound that has two different elements it's 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 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 saltwater solution where 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 Saltwater mixture is the homogeneous mixture because the salt water is distributed uh 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 um 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 mix with each other um in a 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 1 mile is equal to 5,280 ft one mile is also 1.609 kilometers feel free to take notes in one kilometer there are 1,000 m 1 meter is about 100 cm and 1 inch is 2.54 CM there's three feet in a yard and 12 in in a foot 1 millit is equal to 1 cubic cener and 1,000 milliters is equivalent to 1 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 is 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 M how can you convert that to kilomet 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 1 kilometer is 1,000 m now start with what you're given we're going to write 460 M over 1 in the next fraction you need to place the conversion factor but in the appropriate order to 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 th000 so that a th000 is going to be right next to the meters so on top we're going to put 1 kilm so the unit meters cancel and we're going to get km so because the th is on the bottom we need to divide instead of multiply so it's 460 ID th000 whenever you divide by th000 simply move the decimal three units to the left so 460 m is equivalent to 460 kilm let's try another example convert 75 millimeters into cenm the conversion factor is 10 mm is equal to a CM so how would you set it up and what's the answer so let's start with what we have which is 75 mm now since we have millimeters on the top left we need to put it in the bottom right and the 10 is associated with with millimet so let's put that there and 1 cm is going to go on top so these units cancel and it's 75 / 10 which if you move the decimal one unit to the left it's going to be 7.5 cm now let's say if we have a multi-step problem for example if you have 25 kilm how can you convert that into feet so we know that 1 mile is equal to 5,280 ft and 1 mile is 1.609 KM 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 km this is supposed to be Miles by the way not meters 1.609 km is 1 mile so now we can convert miles into feet so we got to put the unit miles in the bottom one mile is equal to 5,2 80 ft and so the unit miles cancel and this is going to give us the answer in feet so it's. 25 divided by 1.609 * 5280 and you should get 82.4 ft 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 3et in a 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 three feet in one yard but because we have a square here we need to square it so we need to divide 36 by 3 2 times or by 9 3 S is 9 so the unit feet squar will cancel and we're going to get yard squared so 36 / 3 is 12 and 36 I mean 12 divid 3 a second time is four so it's four square yards this is the same as 36 ID 9 which is four now let's try another example let's say if we wish to convert 5,000 cubic millimet into cubic cm 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 10 mm is equivalent to 1 cm 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 5,000 by 10 three times or by 10 Cub which is a th000 5,000 ID 10 is 500 500 ID 10 is 50 50 ID 10 is 5 so this is 5 Cub cm or you could say 5,000 / 1,000 is 5 so now you know how to convert from one unit of volume to another unit of volume how would you convert 30 m/ 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 kilomet and kilometers to miles and then we got to convert seconds into minutes and minutes into hours so what's the conversion factor for meters and kilometers there's a th000 meters for every kilometer so the unit meters cancel and we know that between kilometers and miles one mile is equal to 1.609 kilm so kilom 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 seconds into minutes there's 60 seconds in 1 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 / 1,000 * 60 ID 1.609 time another 60 so you should get 67.1 miles hour here's another one convert 25 ft per second into CL km per hour so let's start with 25 ft 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 kilom if you recall there's 5,280 ft per mile and we know that there's 1.609 kilm 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 / by 5280 * 1.609 * 60 * 60 and you should get 27.4 kilom 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^ 12 power Giga is 10^ the 9th power mega represents 10 6 which is a million 10 9 is a billion kilo is 10 3r which is 1,000 now below kilo you have hecto which is 10 squ or 100 and deca which is 10 1st or 10 and below that you have Desi which is 10us one and then CTI which is 10^ -2 and Millie which is 10us 3 and then micro which is 10 -6 Nano that's 10 9 and Pico is 10 to -12 now from this you need to be able to write the conversion factor so for example 1 km is 10 3 m so you can write it like this 1 km is 1 * 10 3 m that's your conversion factor or if you want to write the conversion factor for micro you can say 1 micrometer or um is equal to 1 * 106 m so how would you write the conversion factor for millimet cm and nanometers so let's start with CM 1 cm is 1 * 10 -2 M if you multiply both sides by 100 you'll get this conversion factor 100 cm is 1 M for millimet we could say 1 mm is 1 * 10 -3 M for nanometers 1 nanometer is 1 * 109 M 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 cm 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 centim to met and then met to kilm so let's write out the conversion factors 1 kilm is 1 * 10 3 m which is 1,000 m 1 cm is 1 * 102 M these are the two conversion factors that we need so let's start with 170,000 CM over one let's convert it to meters first so the unit centim has to go on a 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 the 3r and move it to the top x^ -2 is the same as 1x^2 whenever you move an exponent from one side to the other side it change sign so the positive three on the bottom will become -3 when it moves to the top so we can rewrite this as 170,000 * 10 -2 * 10-3 what is 10 -2 * 103 now what is X Cub * x 4 whenever you multiply common bases you are allowed to add the exponents so 3 + 4 is 7 this is X to 7 so therefore 10 -2 * 10-3 is 105 because -2 + -3 is5 so now we need to put the number in appropriate scientific notation we need this number to be between 1 and 10 so we need to with the decimal point five units to the left 1 2 3 4 5 if we do that this is going to increase by five5 + 5 is 0 so it's 1.7 * 10 to 0 anything raised to the zero power is one so the answer is 1.7 km another way you can see it is you need to realize that 170,000 is 1.7 * 100,000 and because 100,000 contains five zeros 100,000 is 10 the 5th and 5 +5 is 0 so you get 10^ 0 which is 1 and so the answer is 1.7 kilm let's try another example try this one convert 380 micromet into CM 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 10-6 so 1 micrometer is 1 * 106 m C he is 10us 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 centim so these units will cancel so now we can do the math so it's going to be 380 * 10-6 and then we're going to take this move it to the top so the -2 will become positive two -6 + 2 is4 so we have 380 * 104 now we need to move the decimal so that it's between the three and the 8 the number has to be between 1 and 10 10 so we need to move a 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 got to add two to it so it's going to be 3.80 * 10 to the -4 + 2 is -2 so this is the final answer in centim try this one let's say if you have 3.6 * 10 four kilm actually instead of kilm let's make it nanometers convert this number into decimeters so how can you convert 3.6 * 10 4 nanom into decimet so just like before we need to go from nanometers to meters meters to decimet so let's write out the conversion factors that we need 1 n is 1 * 109 M Dei is associated with1 so 1 decimeter is 1 * 10-1 m 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 * 109 M 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 * 10 4 * 109 and * 10 POS 1 so 4 + 9 is -55 + 1 is4 so our final answer is 3.6 * 10 to the4 DM 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 g rock was placed in a graduated cylinder that con gain 24.1 M of water the volume went up to 26.2 M calculate the density of the rock the equation for density is mass / volume now let's understand what's happening here so let's say if we have a container that has 24.1 Millers 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 - 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 it's given to us it's 8.4 and so 8.4 G / 2.1 gives us a density of 4 or simply four it's 4 G per milliliter now keep in mind 1 m is the same as 1 Cub CM so we already have the density in gr per cub cmet which is the answer to the first part of the question so now we got to find the density in kilog per cubic meter so we need to convert it so what is the conversion between kilog and g 1 kilogram is 1,00 G kilo represents 10 the 3 which is a th and one meter is 100 cm so let's convert it so there's 100 cm in a meter but we need to raise it to the third power because it a three and to convert grams to kilograms there's 1 kilogram per th G so the unit grams cancel and cubic centimet will cancel as well so we have 4 * 100 cub which is 100 * 100 * 100 and then on the bottom we have a th000 so we can cancel three zeros and so what we now have is 4 * 100 * 10 and this is simply one which will not change the value of anything so 4 * 100 is 400 * 10 that's 4,000 so the answer is 4,000 kilg per cubic meter here's another density related unit conversion problem the price of gold is $42 per gram the density of gold is 19.3 G per cubic cmet what is the value of a rectangular gold bar that is 1x 2x 3 in 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 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 time width time height since we have the volume which is going to be in cubic inches we can convert that to cubic cm and using a density which has grams and cubic centim 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 time width time height 1 * 2 * 3 the volume is 6 cubic in so let's convert it to cubic cenm keep in mind 1 in is equal to 2.54 cm and we need to raise it to the third power so that cubic Ines will cancel now that we have cubic cenm let's use the density to convert it to gr 1 Cub cm 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 * 2.5 4 raised to the 3 power * 19.3 * 42 so this particular gold bar is worth $79,700 and12 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 a number so for example 395 has how many significant figures any nonzero 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 counted as three Sig fix now what about 550 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 some 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 sigic now if we had 5,50 with a decimal point then this zero is counted so we have four Sig fix try these 40 400 how many sig figs are in these numbers so here we have Trail in zero and there's no decimal point so we only have one SigFig 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 0147 7 003 05 70 80 01 05 0 and 0400 0 the zeros to the left which are leading zeros are never counted as significant so we could ignore those zeros so here we have an in between zero which is between the four and seven that's counting so we have four Sig fix 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 fix since we have a decimal point any Zer to the right of a non-zero number are counted and for this one we also have five Sig fix for this one we only have four now what about for scientific notation how many sigfigs 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 fix here we have a total of three and here we have four and in this number we have five sigic 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 Sig fix 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 * 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 fix the second one has two so the final answer should only have two Sig fix so first let's get the exact answer 5.38 * 4.1 so the exact answer is 22058 so how can we round this answer to a number that's close to 22.58% 4.13 find the answer and round it to the appropriate number of significant figures so here we have four Sig fix and in this number we have three so first let's get the exact answer which is 21661 and we can stop there so now we got to 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 1 + 5 6 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 9921 so you need to round to the nearest 10th place so we look at this number since it's less than five we're going to keep it down at N9 if it was greater than five or equal to 5 we would round it up to 10 so the answer for this example is 9.9 now let's say if you have 14753 minus 2.2 this is going to be 336 2 1 that's the exact answer but we need to round it at this position to the nearest hundred's place so since this number is less than five we're going to keep this at three and not round it up to four 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 SC2 and mgcl2 how would you do it mgcl2 is called magnesium chloride SC2 is known as sulfur D chloride so why is it that2 is sulfur D chloride but mg2 is not magnesium D chloride it's simply magnesium chloride why do we use the prefix d 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 SC2 is non ionic it's a molecular or a equalent compound for molecular and equalent compounds you need to use the prefixes like mono die Tri Tetra and so forth mono represents one die is two Tri is three Tetra is four Penta is five hexa is six HEPA is seven OCTA is eight Nana is nine Deca is 10 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 Tetra phosphorus because there's four phosphorous atoms deoxide Deca is 41 now what about this one SE 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 ID now here we have two nitrogen so we're going to say d nitrogen pent oxide or simply pentoxide now let's work backwards what is the formula for phosphorus Tri chloride and also try these as well what's the formula for carbon monoxide and silicon tetrachloride phosphorus Tri chloride so we have a p and we have a CL but we have three CL since we have the word Tri carbon monoxide so monooxide that means we have one oxygen silicon Tetra chloride Tetra means four 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 mono di TR 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 cl4 this is a polyatomic ion it's an ion that contains many atoms poly means many this is called per chlorate cl3 minus this is simply called chlorate per chlorate compared to chlorate simply has one more oxygen cl2 minus is called chlorine eight usually has one more oxygen and I and cl minus is known as hypo chloride hypo means below or less so hypochloride has one less oxygen than chloride CL minus is a monoatomic ion it's an ion composed of one atom mon Atomic ions usually has the suffix ey 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 so42 minus you need to know that this is called sulfate and what do you think s SO3 2 minus is called and S2 minus since s SO3 has one less oxygen than S so4 if s so4 is sulfate s 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 P4 3us P3 3us P3 minus H P4 2 minus and H2 P4 minus p43 minus is known as phosphate so if you know the first one you could find the rest P3 has one less oxygen so if P4 is phosphate P3 is phosphite P3 minus this is phosphide with the IDE ended hpo42 minus this is hydrogen phosphate H2 P4 minus is dihydrogen phosphate now there are some other you need to know CO3 2 minus this is known as carbonate So based on that what do you think H3 minus is what's the name for this particular polyatomic ion hc3 minus is known as hydrogen carbonate or more commonly bicarbonate now what about oh minus C2 H3 O2 minus c22 2us and CN minus oh minus is known as hydroxide C2 h32 minus this is is called acetate c22 2 minus this is oxalate and the last one CN minus is known as cide but now this's more what about cr4 2 minus CR2 07 2us mn4 minus O2 minus O2 2 minus C4 this is called chromate cr207 that's di chromate and the next one M4 minus is permanganate if you see O2 minus where the individual oxygen has a charge of -2 this is called oxide but if you see o22 minus where each oxygen atom has a charge of negative one so two of them has an overall charge of -2 this is known as peroxide and if you see CO2 with a negative 1 charge meaning each individual oxygen atom has an oxidation state of2 if you divide 1 by two this is known as super oxide so these are the different forms of oxide but the most common is just oxide peroxide you may see that occasionally super oxide is rare now let's go over and naming compounds so let's say if we wish to name NaCl which is an ionic compound it has a metal and a nonmetal so the first element simply write the name na 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 ID ending if it's a monatomic ion so this is sodium chloride go ahead and name these elements mg o c a s albr R3 and let's see g n and finally ZN F2 so mg mg is known as magnesium n o the second part it's a monoatomic ion so it's going to be called oxide now what about Casas CA is calcium and for the second element we need to add the IDE Anon 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 Gan GA is called gum and N represents nitride so it's gallium nitride and the last one ZN is zinc and instead of saying F Florine for f it's going to be fluoride the U comes before the O don't put o u it's uo try this b a s so4 let's see l i cl3 K CN NaOH Sr 3 p42 and mg n32 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 cl3 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 pottassium and CN is another polyatomic ion and this one is called cyanide very dangerous stuff now what about NaOH na is sodium and the O minus ion that's a polyatomic ion so that's hydroxide now what about the next one sr3 po42 the first element is called stonum 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 Barum sulfate you need to be able to write the formula calculate the M 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 stes 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 i's 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 5 minus 1 so this represents four now if the I is to the right of the V it represents addition 5 + 1 is six so this is 5 + 2 which is s and it's rare that you'll 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 CCL is copper 1 chloride ccl2 is copper 2 chloride well you might be wondering well that's not bad all you need to do is look at the subscript while 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 1 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 in its compound is neutral if there was an overall charge you'll see like a -2 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 Nega 1 that's what I meant to say so 2 * 1 is -2 to solve for x we need to add two to both sides so therefore X or copper has an oxidation state or charge of plus two so that's how you can find it for the other example it's going to be CU plus CL which equals z so CL is negative 1 if you add one to both sides you'll see that copper is equal to plus one so it's copper 1 chloride okay let's try FES and Fe 2s3 so for FES do you think it's ron1 sulfide since the subscript is one or is it something else so let's find the oxidation state of Fe sulfur has a negative -2 charge so Fe 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 -2 you'll see that Fe has a plus two charge so therefore it's not iron one sulfide rather it's iron 2 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 3 Sufi or is it something else let's find out now let's write an equation 2 Fe plus 3 S has to add up to zero so s has a charge of -2 3 * -2 is -6 and if we add six to both sides it's going to be 2 Fe which equals plus 6 so the solve for Fe we got to divide by two 6 / 2 is three so in this particular case Fe does have a plus three 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 SN O2 so even though lead and Tin are not transition metals they do have multiple oxidation States typically plus2 and plus4 so you know that oxygen has a negative -2 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 2 oxygen atoms equals to a net charge of zero and each oxygen has a charge of 2 so 2 * -2 is4 if we add four to both sides 10 is in the plus4 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 form formula for lithium chloride the first thing you should do is write the ions lithium as an ion has a plus one charge it's an alkaline metal has one valence electron and elements in group 1 a 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 ratio so another example of this is calcium selenide calcium is an alkaline earth metal with a plus two charge and selenium is a calogen 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 to1 ratio another example is aluminum nitride aluminum is in group 3A of the periodic table so it has a plus three charge and nitride is a group 5 a element and it has a minus three charge so here the charges are the same so you can simply write them as a out n 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 mg1 br2 but if you have a one you don't really need to write the one so is simply mgbr2 now what about aluminum sing aluminum has a plus three charge and sulfate this is where you need to know your polyatomic ions It's s so42 minus so using the crisscross method it's going to be al2 S so4 3 now whenever you have multiple polyatomic ions you need to enclose it within a parenthesis now 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 p43 minus so using the same crisscross method it's going to be na 3 P4 now we don't need to write the one so we can simply leave it as na3 P4 now what about this one lead for sulfide feel free to pause the video and try this example so in this particular case the four tells us that lead has a plus4 charge sulfur has a Nega -2 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 two 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 nonmetal it's an acid now there's some things that you need to know eight is associated with I when writing the name of the acid I is associated with is and and I will have the prefix hydro and the suffix i 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 eight part we know we need to replace it with I so to write the name of the acid write the element first which is sulfur and then add the suffix i 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 is 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 suurus 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 with the suffix i and then let's add the word acid so this is called Hydro sulfuric acid now what about this one hcl4 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 cl4 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 CL is the polyatomic ion hypo chlorite so let's replace I with is so to name the acid it's simply going to be hypo chloris acid now what about HCL how can we name that acid so the anine CL minus is known as chloride because it has an IDE end in we need to add the prefix Hydro and then instead of saying chlorine after the r we're going to add I 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 I with a so this is associated with the phosphate polyatomic ion phosphate is p43 minus once you've identified the ion you simply need to add hydrogens to it because the charge is neg3 we need to add three hydrogens to it so it's going to be H3 P4 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 I with eight so we need to write the polyatomic ion carbonate carbonate is CO3 2 minus and since it has a -2 charge we got to add two hydrogen to it so the name of carbonic acid or the formula for it is h23 now what about this one Hydro bromic acid so because we have the prefix hydro and the suffix i It's associated with I or bromide and bromide is a monoatomic ion which is BR minus because it has a Nega 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 I part with eight It's associated with the polyatomic ion iodate now now chlorate was cl3 minus iodate is io3 minus the Helens 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 a with eight this is associated with acetate acetate is C2 h321 so we need to add one hydrogen to it so the formula is hc2 h32 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 1 kilogram is 1,000 gr 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 12 eggs 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 avag God's number which is 6.02 * 10 23 so if you have a mole of pencils you have 6 * 10^ 23 pencils if you have a mole of atoms you have 6 * 10 to 23 atoms and so a mole is just a very large quantity now there's something called 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 M mass of carbon and the units for M mass is 12.01 G per Mo so as you can see molar mass is simply the mass divided by moles gr over moles now let's say if you wanted to calculate the mol 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 1.8 but times 4 since we have four hydrogens so let's round it and let's say this is 12 and hydrogen is one so the M mass of methane is about 16 G 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 1 so sodium hydroxide has a m mass of 40 G per Mo so what this means is that one mole of sodium hydroxide has a mass of 40 G so 2 moles of sodium hydroxide will have a mass of 80 g so mol mass is simply the ratio between grams and moles now what about the M mass of glucose C6 h126 now what's the answer so there's 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 6 and 12 is 72 and 6 * 16 is 96 72 and 12 that's 84 and 84 and 96 that's 180 so the mol mass of glucose is 180 g per mole so one mole of glucose ose has a mass of 180 g 2 moles of glucose has a mass of 360 G 3 moles of glucose has a mass of 540 G 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 divide by the total masstimes 100% 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 * 100% And so you're going to get 75% 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 mol mass of hydrogen divided by the total mass 4 out of 16 * 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 + 16 + 1 which is 40 so at this point if you type it in 23 40 * 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 in sodium hydroxide so the mass of hydrogen is 1id by a total mol mass of 40 so it's 1 out of 40 * 100 so it's 2.5% % by mass for hydrogen now what about for oxygen since oxygen is the last element we could simply do 100 minus 57.5 - 2.5 or 100 - 60 so that means that it's 40% 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 6 * 12 that's the total M mass of all the carbon atoms in glucose now the total M mass for all of the atoms in glucose is 6 * * 12 + 12 + 6 * 16 * 100% so the 6 carbon atoms has a m mass of 72 the M 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% 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 GRS into moles so for example let's say if you have 48 G of carbon how many moles of carbon is this equivalent to so whenever you want to convert from grams to moles or moles to GRS you need the M Mass based on a periodic table the M mass of carbon is 12 so what that means is that one Mo of carbon has a mass of 12 G 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 Mo of carbon is going to go on top so that these units cancel so it's simply 48 over2 which is equivalent to 4 moles of carbon now let's make sense of it so the molar mass is 12 and as we mentioned before one Mo of carbon is equal to 12 G so 2 mol of carbon is equal to 24 G 3 mol of carbon is equal to 36 G so for every mole of carbon that you add the mass increases by 12 so four moles of carbon equates to 48 G of carbon which is the answer that we wanted now try this example so let's say if you have 22 G of carbon dioxide go ahead and convert it to moles of CO2 so the first thing you need to do is find the mol mass of CO2 the atomic mass of carbon is 12 and for oxygen is 16 but there's two of them so 16 * 2 is 32 + 12 that's 44 so the M mass is 44 G per mole so now let's start with what we're given and we need to put GRS on the bottom so there 44 G of CO2 per 1 Mo of CO2 so whenever you need to convert from GRS to moles take the mass in gr and simply divide it by the M Mass so 22 ID 44 is .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 gr you need to multiply the moles by the M Mass so let's say if we have 3 moles of neon let's convert it to gr of neon so let's start with what we're given now if you use the uh prct table if you take a look at it you'll see that the atomic mass of neon is approximately I'm going to round it it's about 20 G per mole so there's 20 G of neon per 1 Mo 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 * 20 is 60 so you're going to get 60 G of neon try this one let's say if you have five moles of c2h6 molecules convert this into grams of C2 H6 c2h6 is ethane so let's find The M 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 + 6 is 30 so it's 30 G per mole so let's start with 5 moles of ethane let's convert it to grams so there's 30 gr of ethane per one mole of ethane therefore the unit moles of ethane will cancel and so it's 5 * 30 we know 5 * 3 is 15 so 5 * 30 is 150 you got to add the zero so we have 150 g of ethane so that's how you can convert from to G using M Mass so if you want to write an equation the moles is equal to well let's actually write it this way mass in gr is equal to the molar mass times the moles so let's use lowercase M for mass and let's use C capital M for M mass and N for moles be careful though capital M sometimes could be marity so watch out for that so mass is mol mass time 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 if you have three moles of carbon how many atoms do we have so to answer this question we need to use avag God's number 1 mole is equal to 6 * 10 23 it's really 6.022 * 10 23 but I'm going to round it to 6 * 10 23 so let's start with three moles of carbon 1 Mo of carbon is equal to 6 * 10 23 atoms of carbon so that's how you can convert from moles to atoms simply multiply by avag God's number so the answer is 6 * 3 that's 18 so it's 18 * 10 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 anytime you move the decimal one unit to the left the exponent needs to go up by one so you have to add one to 23 so it's 1.8 * 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 mo Ule is a particle that is composed of many atoms so when using avagadro's number one mole of methane corresponds to 6 * 10 23 not atoms of methane but molecules of methane since CH4 is a molecule so if we simply multiply 4X 6 * 10 23 that's all we need to do to get the molecules of CH4 so that's going to be 24 * 10 23 which is the same as 2.4 * 10^ 24 molecules of CH4 now if we want to find the atoms of hydrogen we 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 4 so 4 * 6 is 24 24 * 4 if 20 * 4 is 80 4 * 4 is 16 80 and 16 is 96 so 24 * 4 is 96 so it's 96 * 10^ 23 atoms of hydrogen which is the same as 9.6 * 10 to 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 G 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 moles to atoms you can't go directly from grams to atoms so to go from grams to moles we need the M Mass the atomic mass or M mass of helium is about four it's four G per mole so 4 G of helium equates to one Mo of helium so these units cancel and now we can convert moles to atoms one Mo of helium is 6 * 10 to the 23 atoms of helium so it's going to be 16 / 4 which is 4 4 * 6 is 24 so 24 * 10 23rd is 2.4 * 10^ the 24th atoms of helium now let's say if you have 3 * 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 alagad number so one Mo of argon atoms is equal to 6 * 10 23 atoms so the unit atoms cancel and now we can go from moles to GRS the M mass for Argon is about 40 so there's 40 gr of argon for every mole of argon so those units disappear so now let's do the math we can cancel the 10^ the 23r because they're the same 3 / 6 is a half and half of 40 is 20 so the answer is 20 G of argon so now you know how to convert from atoms to grams now let's uh 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 reaction so let's say if you have propane which is C3 h8 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 the substances the subscripts are the small numbers like the three the eight the two those are the subscripts you can't change those when balancing the equation you can only change it when writing a 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 balancing 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 8 ID two is four so let's put a four in front of H2O now you want to save the oxygen atoms for last so 3 * 2 is 6 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 6 and four is 10 so we have a total of 10 oxygen atoms on the right side so what number do we need to put in front of o2 to balance it well 10 ID by the subscript 2 is five so we need a five in front of o2 and since we don't need a number here we could put a one 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 c2h5 which is known as ethanol plus O2 produces carbon dioxide and water go ahead and balance this particular combustion reaction to 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 5 + 1 is 6 6 / 2 is 3 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 4 + 3 is 7 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 1 + 6 is 7 so 6 / the 2 is 3 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 4 and 3 which is 7 1 and 3 * 2 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 Redux reactions what would you say consider this reaction butane plus oxygen produces CO2 and water here's another combustion reaction it turn 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 Redux 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 ele element in the compound then it's a reduxx reaction so here we have a Pure Element and here's a compound if you see that it's definitely going to be Redux now how would you balance this combustion SL redox reaction so let's start with the carbon atoms we have four on the left so we need to put a four in front of CO2 now we have 10 hydrogens on the left side 10 / 2 is 5 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 13 13 / 2 is 13 / 2 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 2 C4 h10 now 13 over 2 * 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 * 2 is 20 and 26 oxygen atoms 8 and two 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 make A and B and you get a single product that's known as a combination reaction not every combination reactions are Redux reactions some are some are not now if you mix a metal and a nonmetal 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 two cation bromine is going to acquire the electron 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 ZN br2 and the reaction is already balanced so is this reaction a Redux 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 zc bromide individually has an oxidation state of negative 1 because bromide typically forms a negative 1 charge whenever the oxidation state increases the substance is oxidized so the oxidation state of zinc went from0 to plus2 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 0 to1 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 substance zinc to be oxidized Metals most metals particularly the active ones are usually good reducing agents because they like to give away electrons nonmetals 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 set to be reduced now let's say if we were to mix calcium oxide and water calcium oxide is a basic and hydde metal oxides are considered basic and hydrates 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 O It's a base bases produces hydroxide ions in solution so notice that this is a combination reaction it's in the form a a plus b turns into a now this particular combination reaction which is already balanced is it a Redux 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 Redux 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 Redux or is it not a redox reaction notice that we have a compound compound compound no pure elements so it's not a reduxx reaction now let's say if we have magnesium nitride which is a solid if we add heat to it what's going to 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 three in front of mg so is this a reduxx 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 reduxx reaction here we have a compound and here we have a Pure Element so it's a reduxx reaction now there are some other common decomposition reactions that you should know the decomposition of potassium per chlorine if you had 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 a gas can be form is going to drive the reaction to the right making it spontaneous so both of these are decomposition reactions now are they Redux reactions if you look at the first one we have a compound and here we have a Pure Element so it's a redo reaction for the second one compound Pure Element Redux to balance the first one notice that we have three oxygen 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 K3 and a three in front of o2 so we have six oxygen atoms on both sides notice that we have two potassium atoms so we got to put a two in front of KCl now it's balanced for mercury oxide all we got to do is put a two and a two 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 and hydrides now what about non-metal oxides like sulfur dioxide non-metal oxides are acid and hydrides because when you put them in water they will turn into an acid so SO2 plus water turns into H2S SO3 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 nonmetal oxides are acid and hydrides metal oxides are basic and hydrates 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 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 could leave as 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 hydroc choric acid what are the products of this 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 his 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 us gas aluminum is a solid HCL is aquous which means that it's dissolved in water aluminum chloride will also be in aquous 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 is dissolved in water now this single replacement reaction is it a redox reaction it turns out that all single replacement reactions are reduxx reactions notice that we have a pure element and a compound so it's a reduxx reaction now which substance is oxidized and which one is reduced so aluminum is in the zero oxidation state because it's Pure Element but in this compound is+ three now hydrogen is in the +1 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 0 to three so the oxidation state goes up so alum aluminum was oxidized now hydrogen in HCL it went down or it was reduced from 1 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 reducing 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 going to 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 we have six hydrogen atoms in 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 Al now the reaction is balanced now consider this reaction let's say if we have an aquous 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 aquous to know this you need to understand the solubility rules nitrates acetates ammonium which is nh4+ are always soluble alkaline 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 ag1 and cl minus one because these two have the same charge even though the sign is opposite we can write them in a one: 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 aquid 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 and 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 n32 whenever you have multiple polyatomic ions make sure you enclose the polyatomic ion within a parenthesis now we said nitrates are always soluble so magnesium nitrate is going to be Aquis 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 got to put a two in front of H3 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 Redux 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 Redux 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 and it's particular example the first thing that you need to do is write the total ionic equation so everything that is in the aquous phase we need to separate it into ions except the solid so we have two ag+ ions and two nitr ions in ag3 in this compound mgcl2 we have a magnesium ion and two chloride ions agcl is a solid so we're going to leave it that way everything that we separate into ions all of these are in the aquous phase by the way and then magnesium nitrate we could separate that into mg+ 2 or mg2+ 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 Spectator ions are those that do not participate in a reaction they just spectate they watch so on a reaction they look exactly the same the nitrate ions are spec ions we can cancel them out and magnesium is a specon so what remains is the net ionic equation which is 2 ag+ plus 2 CL minus produces two agcl notice that each of these has a coefficient of two which means we could divide each 1 by two so it simplifies to this ag+ which is in the aquous phase and cl minus which is also in the Aquas 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 mix sodium hydroxide with sulfuric acid so this is an acidbase 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 Redux reaction so the two on the outside will pair up sodium has a plus one charge and sulfate has a -2 charge which is important for you to know the polytomic iist 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 anic equation so you have to make sure you know your polyatomic ions so if we paare these two ions together it's going to be na 2 so41 or just s so4 so that's one of products that we have to find the other product whenever you pair H with o these two will just create water this is something that you should just know or commit to memory so now we have a balanced 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 two 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+ 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 in aquous phase sodium hydroxide is soluble in water na is an alkaline metal alkaline metals are always soluble now acids for the most part are soluble in water I never seen an acid that doesn't dissolve in water and water is a liquid so to write the total ionic equation everything that's in the aquous phase we need to separate into ions so we're going to have two na+ ions from o and two hydroxide ions now in the next compound suric acid we have two H+ ions and one sulfate ion in sodium sulfate there are two sodium ions and a sulfate ion and water is a liquid so it's not aquous therefore we need to leave it the way it is so what are The 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 2 H+ 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 aquous phase plus one H+ ion or hydrogen ion in aquous 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 stochiometry I've created one that's entitled stereometry grams moles atoms molecules it also has examples on limiting and excess reactants percent yield retical yield things like that and I've created another one on solution stochiometry where it goes over mity calculations and how to convert from grams to moles to marity to liters and things like that and how to do dilution problems using the M1 V1 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