hello everyone today we are going to start discussing chapter four which is all about atoms and elements and this chapter is extremely important to really understanding the fundamentals of chemistry so this lecture will cover the eight sections in chapter four that focuses on atoms and elements and so first we're going to go to go ahead and start with elements and symbols so a chemical symbol is a one or two letter abbreviation used to represent an element and so let's look at some examples number five on the periodic table is boron and this is represented as a capital b we have the next atom over which is carbon number six on the periodic table is represented as a capital c you have lead which is uh down in the bottom on the right hand side of the periodic table this is represented as pb because of its greek name plumbum but we know it as blood so the representation the two letter abbreviation may or may not correlate to the name that we're used to so you will have a periodic table to to utilize so you do not need to remember all of the one or two letter symbols for each of the elements on the periodic table so a chemical symbol is a one or two letter representation for an element on the periodic table so now let's go ahead and talk about the periodic table so section 4.2 is the periodic table and in this section we are going to learn about uh the periodic table but let's first learn some terminology so you have a group or a column i will be calling them columns but you may hear it as a group and a group is a family of elements with some similar pop properties a family of elements with similar properties so the properties are similar within a column so for a group again we're looking at a column and uh the way that you remember this is columns will build buildings up and down so it is vertical so a column is a vertical representation on the periodic table and the this family shares similar properties of one another that's a group we also have a period and you will not refer hear me reference as group or period i like to use column rows a period is a row on the periodic table and this is just a family of elements in a row okay so it's a little bit different it's not grouped as it's not grouped in the same way that a column is a period is a row of the periodic table and they don't necessarily have similar properties but they are all within a row of one another and so again columns share properties and rows are the way that the periodic table is set up so let's go ahead and look at how the periodic table is set up this is the periodic table of elements that is from your textbook i'm going to go ahead and highlight it in this tan color this is the periodic table and so when we're looking at our periodic table our columns are up and down are horizontal excuse me vertical a column is a vertical group and then we had our rows which is the horizontal group so a row or a period and we either call this a column or a group so remember the groups have the columns have the same chemical properties or similar chemical properties and so uh lithium sodium potassium rubidium cesium and franzium all this first group here on the periodic table all share similar properties of one another because they're all in the same column the same is going to be true and we're looking over here on the right hand side of the periodic table all of these in the very last column are also that i'm highlighting in yellow are also going to share chemical properties uh the same similar chemical properties as one another so let's go ahead and name everything on the periodic table you'll have the periodic table to use uh for all exams and everything like that you do not need to memorize this so here is the different groups of the periodic table and again they're uh a group by definition is a column on the periodic table and it's a family of elements so it's a group or a column i like column better a family of elements that share chemi that share chemical properties so the very first group that we have is group one or one a and those are called the alkali metals second over we have uh column two a or group two a and those are called the alkaline earth metals this is uh 3b 4b 5b 6b7b 8b 9b b 11 b and 12 b and these are all called the transition metals in that periodic table over here in blue these uh 3a through 6a have no common names they're just there's no common names then 7a are the halogens and those all share symbol similar chemical properties and then last but not least that last row is called the noble gases and those are always going to share the same chemical properties and then you'll see two rows down here and the first is called the lanthanides and then the actinides and this block and i'm going to go ahead and highlight this block in green since we haven't used green yet the block that's underneath the periodic table is typically very uncommon we don't really focus on those two rows necessarily in this class so the other thing that we want to know about the periodic table is most elements on the periodic table are metals and metals are shiny solids and this is most elements on the periodic table so we'll have see some metals we'll also see some non-metals and this is the group that typically the ones with no common names a lot of those happen to be non-metals halogens and noble gases are also non-metals and these are not shiny ductile um they're not shiny they tend to be ductile and malleable these are core conductors of electricity and the last group on the periodic table are the metalloids and these are not as common but there are these groups on the periodic table um and i'm going to go ahead and highlight them in orange so the ones that are along this stair step on the periodic table happen to be metalloids so those were those lie on the periodic table and these are elements that exhibit both metal and non-metal properties and so we will discuss all of this later on but those are just some more definitions so we have our metals which happen to be shiny solids and those are most elements on the periodic table happen to be metals you have your non-metals which are not shiny um they're ductile and they happen to be more malleable they're poor conductors of electricity organic chemistry focuses a lot on the non-metal portion of the periodic table and last but not least we have metalloids which are on the stair step and those exhibit both metal and non-metal properties so they're not very common commonly used elements when they are used they're very functional but they're not necessarily commonly used elements on the periodic table so that's section 4.1 and 4.2 so let's go ahead and talk about section 4.3 next which is the atom and this is again really important in understanding chemistry and understanding the uh what's actually going on in chemical reaction so you have dalton's theory and his theory stated four different things and the first is that all atoms all um everything all particles are made up of atoms so that's the first thing that was said was that all particles are made up of atoms the second thing that he said is all atoms of a given element all atoms of a given element are the same as each other and different from any other element so all carbon atoms are the same but they're always going to be different than any boron atoms that's what we're saying there and so all atoms of a given element for example boron are the same as each other so all boron atoms are the same as one another but they're all different than any other element on the periodic table so no boron atom is like a carbon atom no boron atom is like a magnesium atom but all boron atoms are the same atoms plus elements form compounds so two or more elements form compounds so if you have a compound that means that you have two or more elements and the last thing that was stated is that a chemical reaction reaction rxn a chemical reaction involves rearrangement of atoms and that rearrangement can be a separation of atoms it can be a combination of atoms it could be the atoms just simply rearranging but something has to happen in order for a chemical reaction to proceed and so somehow though this atoms need to be rearranged so dalton's theory was four different things all particles are made up of atoms all atoms of a given element are the same as one another but different from any other element two or more elements form compounds and a chemical reaction involves the rearrangement of atoms that's what was stated so now let's go ahead and look at the electrical charge in an atom we still haven't really defined what an atom is but we're now looking at the electrical charge of an atom so inside the nucleus you have things called protons and those protons have a positive charge outside the nucleus you have and this is not a correct representation of the atom it's just showing that inside the nucleus you have protons so inside the nucleus you have protons and protons again we're looking at the electrical charge of an atom inside the nucleus you have protons and those have a positive charge one unit of positive charge and so that is a proton one unit of inside of uh a proton is one unit of a positive charge and that's found inside the nucleus you also have a neutron and i do not have that shown on this diagram which is no problem this is also inside the nucleus this has no charge so it's not really going to influence the way that the molecule is necessarily going to behave so a neutron is inside the nucleus and that has no charge so that is a neutron and we'll talk about neutrons those again are inside the nucleus and those have no charge and then last but not least we have outside the nucleus again my representation of the atom is not correct we have the outside the nucleus you have an electron and that is one unit of negative charge so outside that nucleus we have an electron and that has a negative charge so we have a negative charge and a negative charge and a negative charge outside the nucleus inside the nucleus you either have positive charge or no charge so that is the electrical charge of the atom again we still haven't really talked about what that means but inside the nucleus we have protons and neutrons and outside the nucleus we have an electron again we still haven't talked about uh what that means we will talk about that later in this chapter we're just setting the stage of what is to come so let's go ahead and look at the mass of an atom we're only going to be looking at the proton and the neutron so a proton which has one unit of positive charge has a mass of again we're looking at the mass a proton has a mass of 1.67 times 10 to the negative 24 grams an electron which is one unit of negative charge has a mass of 9.11 times 10 to the negative 28 grams so we can see that both of these numbers are very small but what we'll also notice is our mass of our proton is much greater than the mass of our electron and that's because that negative number is smaller um a proton has a mass of 1.67 times take 10 to the negative 24. and elect one single electron has a mass of 9.11 times 10 to the negative 28. so these units are or are typically difficult to work with because again we don't want to have to constantly use these exponential factors in every single calculation so what we can do is use an amu and an amu means an atomic mass unit and this is going to be helpful so we have amu and that's abbreviated for an atomic mass unit and that's really helpful because this allows for us to ignore or not really consider those exponents so when atomic mass units allow us to use the numerical values in calculations without using the exponents because again those exponents when we need to start calculating things those exponents are very large or excuse me very small um and so they can get quite uh quite annoying to you so instead of actually using the mass of a proton and the mass of an electron we use this thing called an atomic mass unit and that allows for individuals to actually carry out calculations without having to take into account that exponent and the way that we calculate this atomic mass unit is we need to have a standard we need to be able to compare everything so we use carbon-12 it's just the standard that we use and what we're saying is for carbon-12 that has 6.02 times 10 to the 23rd atoms that's a lot of atoms taking into account the 12 protons excuse me the six protons and the six electrons and the six neutrons so this is six protons six neutrons you're not expected to know this yet in six electrons so we have six protons six neutrons and six electrons when we add all of those up in 6.022 times 10 to the 23rd atoms that is going to equal 12 grams so 6.02 times 10 to the 23rd atoms of carbon will atom will have six protons six neutrons and six electrons if we take the mass of all of those atoms 6.02 times 10 to the 23rd atoms that will give us 12 grams of uh carbon so this is what we use as our standard to compare all other elements on the periodic table so again that way that of allows us to not use those exponents because again those can get in the way of calculations and they can make um calculations to be difficult so again we haven't really discussed but any of this means we are just laying the groundwork so that that way we can discuss what all of this means um in future material in this chapter as well as other lectures as well so let's go ahead and look at 4.21 together so 4.21 true or false that's what we're asking true or false one we want to ask or we're asking are protons and electrons do those have opposite charges protons have a positive charge electrons have a negative charge excuse me not an e electrons have a negative charge so yes those are opposite charges and so what we're going to say is that this is a true statement because yes those are opposite charges so question b is asking the nucleus contains most of the mass of an atom so again we're looking in we want to think about what's going inside that nucleus protons and those have a molecular mass of 1.67 times 10 to the negative 24 grams outside the nucleus we have our electrons outside the nucleus we have 9.1 for every electron 9.11 times 10 to the negative 28 grams and so inside the nucleus we have a much larger amount of material so again this statement is true so let's go ahead and look at c and what we're asking is that electrons repel one another we're asking ourselves is this statement true or is this statement false so you have one electron with a negative charge and you have another electron with a negative charge and so think about this in terms of a magnet opposites attract one another so these two electrons are absolutely going to repel one another so when you put a magnet on the refrigerator it's attracted to the refrigerator when you hold two magnets of the same pull towards one another they are harder to push together and that's because those electrons are repelling one another so yes this is a true statement now let's look at d and d is saying that protons are attracted to the neutron protons are attracted to neutrons so remember protons have a positive charge and neutrons are going to have an overall zero charge there's no charge to a neutron so a positive charge is not going to be attracted or unattracted to a net zero charge uh because they're not opposites of one another so this is a false statement so uh again that's what's going on inside and outside the nucleus of an atom so now let's talk about what actually defines an atom is it the protons is it the neutrons or is it the electrons so this is section 4.4 the atomic number and the mass number so section 4.4 is all about the atomic number and the mass number so your atomic number is the number of protons this is really important your atomic number is the number of protons i'm going to highlight this in this bright purple color your atomic number is the number of protons that you have it is not the number of electrons so your atomic number is the number of protons and it's not necessarily the number of electrons it can be but it's not necessarily the number of electrons so let's go ahead and look at for example lithium lithium will have an atomic number of three that means that lithium is going to have an atomic number of three that means lithium is going to have three protons again we're not really thinking about the electrons at this point not yet but we will the mass number uh let's let's look at carbon um carbon because we're going to talk about carbon's mass number so carbon has an atomic number of six so carbon has an atomic number of six and so that means carbons has six protons it may have six electrons it may not so the atomic number is what is uh the number of protons and that determines the element on the periodic table now let's look at the mass number so we've looked at the atomic number that's the number of protons your mass number is the number of protons and neutrons again everything that's going on inside the nucleus not outside the nucleus the number of protons and neutrons so remember you find your protons and your neutrons in the nucleus so we're not even talking about anything going on outside of the nucleus your mass number are the number of protons and the number of neutrons so you'll see carbon 12. so what we can say is that we have 12 neutrons plus protons because that is the definition of the mass number carbon is number six on the periodic table so you have the number of protons and so 12 minus six is equal to six so you have six neutrons so inside the nucleus of a carbon atom you have six protons the number of protons and so we find that by um the number on the periodic table carbon is number six the sixth element on the periodic table so you have six protons inside the nucleus carbon has an atomic number of excuse me a mass number of 12 and that is the mass number is equal to the number of neutrons and protons so that is equal to six neutrons so you have six neutrons inside the nucleus as well because remember by definition that mass number is the number of protons and neutrons and so that is this number here and that's the number that we will find on the periodic 12. so let's look at 4.3 together so 4.3 is zinc is a micro mineral and it's needed to metabolize uh reactions and cells and dna synthesis it's used in the growth of bones t teeth connective tissue and proper functioning of the immune system for an atom of zinc it has a mass number of 68 so we have a mass number of 68. let me go ahead and fix that so that it's all blue a mass number of 68 and so the question is asking us to determine the number of protons neutrons and electrons so we have a mass number of 68 so let's just go ahead and write our 68 and zinc that's the element that we're looking for on the periodic table it's two-letter abbreviation is zn so you can find that on the periodic table you again you'll be able to use the periodic table on your exams and everything so you should always have a periodic table available for you for your homework what you'll find is that zinc is number 30 on the periodic table so because zinc is number 30 on the periodic table we must have 30 protons because the atomic number is your number of protons which is also the number of the element on the periodic table so zinc is number 30 on the periodic table so we're going to go ahead and write that our mass number is the atomic number the number of protons plus the number of neutrons from the mass number we can subtract out the number of protons and that will give us the number of neutrons so our mass number of zinc happened to be 68 it happens to be 68 and we have 30 protons so that would leave us 38 neutrons 68 minus 30 will leave you 38 neutrons and under normal circumstances not always but under most circumstances the number of protons and the number of electrons are going to be the same and so if you have 30 protons you need to have 30 electrons and we will talk about when this is not true later on we're not talking about um then when you have a varying number of protons and electrons yet we will get there so as of now your number of protons and your number of electrons are the same let's think about why that is i'm not going to use zinc as the example because again we have 30 and that's a lot to draw but let's go ahead and look at hydrogen the most basic element on the periodic table hydrogen hydrogen is number one on the periodic table it's the first element on the periodic table therefore we know we have one proton right now we're not talking about elec uh neutrons we're just discussing why neutral atoms have the same number of protons and electrons so when you're looking at inside the nucleus of a hydrogen atom you have one proton and so outside of the nucleus you have one electron so plus one inside the nucleus minus one is equal to zero and so this is your overall charge and elements on the periodic table are neutral meaning they have no charge so what's going on inside that nucleus you have one positive charge has to also be going on outside of the nucleus so you have your plus one going on inside the nucleus that's your proton and you have your minus one going on outside the nucleus is your electron and again we haven't talked about any elements that have a charge yet we will get there in a different chapter so zero is the overall charge for now what you're looking for zero is always going to be the overall charge i mean that means again we want to think about this in terms of inside the nucleus and outside the nucleus are the same that's not always going to be true um chemical reactions happen when there's an imbalance of inside the nucleus and outside the nucleus but right now we're not talking about chemical reactions we're only trying to understand how the atom is set up so let's go ahead and look at problem 4.31 here's a periodic table that you will be able to use so here's the periodic table to use again i would strongly recommend having this for your homework and here is the sample question it's asking you to complete the following table um for elements that are essential to the body so we have zn which we just looked at that is going to be number 30 on the periodic table zinc right here number 30 on the periodic table the name of the element is zinc it has an atomic number of 30 that's the number of protons and you'll find that number up here where i'm highlighting currently in blue that is the atomic number the mass number is 66 so that means that you have 30 protons and you have 30 electrons so therefore you must have 36 neutrons zinc so we're looking for atomic number 12 so we're going to look for atomic number 12 on the periodic table this is magnesium mg and so we're going to be looking at magnesium magnesium is atomic number 12. that must mean that it has 12 protons and 12 electrons i have 12 neutrons so therefore i must have an mass number of 24. potassium is k on the periodic table so that has a one letter symbol of k the atomic number of potassium is 19. so that must mean you have 19 protons and 19 electrons we have 20 neutrons so therefore we have 39 as our mass number we're looking for a number of protons which is going to be the same number as the atomic number of 16 and that is sulfur right here on the periodic table underneath oxygen sulfur that is a chemical representation of s it has 16 protons so therefore it must have 16 electrons 16 elec protons plus 15 neutrons is going to give you a mass number of 31 and last but not least we have a mass number of 56 and a number of electrons is 26. again we're only looking at neutral elements so the number of electrons have to equal the number of protons for now so 26 protons so we're looking for 26 on the periodic table which is iron chemical representation fe iron has an atomic number of 26 and it has a 26 protons and a mass number of 56 so therefore it must have 30 neutrons so there is 4.32 which you'll also have as your homework so i would definitely practice completing these tables and really understanding what each of those mean now we're going to talk about isotopes isotopes is section 4.5 and isotopes is still what's going on inside the nucleus we haven't talked anything about what goes on outside the nucleus so right now we're assuming outside the nucleus is uh the same as inside the nucleus we have not talked about what happens when something goes on outside the nucleus so isotopes and atomic mass remember your atomic mass is the number of protons so an isotope is going to be a varying number of neutrons a varying number of neutrons your atomic mass your number of protons that can never vary for a specific element on the periodic table that is never going to change all lithium is atoms are always going to have three protons that's not going to change there are special circumstances where it does we are not talking about that in this class whatsoever so you can assume that the number of protons can never change so when we're talking about an isotope we're still talking about what's going on inside the nucleus and that's going to be a varying number of neutrons so let's go ahead and look at our hydrogen atom again so for a hydrogen atom inside the nucleus you have one proton and outside the nucleus you have one electron so we have one proton and we have one electron again we're talking about isotopes so we're not talking about what's going on with the proton or the electron in a normal hydrogen atom you have zero neutrons in a hydrogen atom you inside the nucleus you can still have one proton and again that is going to be your atomic mass that is the definition of an element on the periodic table the proton count is never going to change right now we're not looking at all what's going on outside the nucleus so we can still assume that we have one electron and if we add one neutron into that nucleus we're adding no charge it has a zero charge but what we're doing is we still have one proton and we have one electron and now we have one neutron so again we're not adding there's no charge change we're not adding any chemical charge the protons are positively charged the electrons are negatively charged the neutrons are zero charged but now we have one neutron and so that is going to change the mass of hydrogen but nothing else so when we have one neutron this is called deuterium it doesn't change anything except for the mass of the element itself and so that is where you have one neutron so now again let's look we're still looking at that hydrogen atom inside the nucleus we have one proton because we're not looking at the atomic number outside the nucleus we can assume we stop one electron because we have not discussed what happens when you have varying electron counts but inside the nucleus now we have two neutrons so inside the nucleus we still have one proton because again that cannot change we're still talking about the hydrogen atom outside the nucleus we still have one electron because we haven't talked about electrons at all um so we can assume the number of protons is equal to the number of electrons now inside the nucleus we have two neutrons again this has a positive one charge the electron has a negative one charge and inside the nucleus we have two zero charges so we're not changing the overall charge but this is called tritium and that is still a hydrogen atom with two electrons uh excuse me with two neutrons with two neutrons that is tritium so again you're not changing the chemical charge whatsoever but you are adding two neutrons so isotopes make heavier atoms but no other change and isotopes exist for many elements on the periodic table not all of them but many of them so when we're looking at elements on the periodic table we want to think about our atomic mass not our atomic number our atomic mass how much does an atom weigh the atomic mass and what this does is it takes into account so the definition of atomic mass is how much an atom weighs and this takes into account it takes into account each isotope and we're going to see an example of this and the percent of each isotope so what does this actually mean let's let it look at an example we're going to look at magnesium magnesium has three three stable isotopes so let's go ahead and look at the isotopes of magnesium we have magnesium 24 so we're going to look at our proton count our electron count our mass number all of magnesium the isotopes and magnesium our neutron count which has no charge the mass isotope which we're going to call our atomic mass unit or amu so we don't have to use those exponents and last but not least we're going to look at the percent abundance of each of these group so you have again we're looking at magnesium magnesium has three isotopes it has magnesium 24. and magnesium is number 12 on the periodic table and as isotope number 25 and it has isotope number 26. all of these isotopes exist in magnesium so magnesium exists in uh in abundance on the earth and it has the isotope 24 25 and 26. so magnesium is always going to have 12 protons that is what we are going to define as magnesium is that it's always going to have 12 protons it doesn't matter what the isotope is so therefore if we have 12 protons we can assume for now we have 12 electrons and that's because the number of protons and the number of electrons are the same here we have our mass number of magnesium or three different mass numbers so for magnesium 24 our mass number is 24. for magnesium 25 our mass number is 25 and for magnesium 26 our mass number is 26. so now let's go ahead and look at our neutrons so uh 12 minus or 24 minus 12 is going to give you 12 neutrons 25 minus 12 is going to give you 13 neutrons and 26 minus 12 is going to give you 14 neutrons so in magnesium 24 the only difference for magnesium 24 is that you have 12 neutrons magnesium 25 you have 13 neutrons and magnesium 26 you have 14 neutrons and again neutrons have no charge so you're changing the mass of the element so your atomic mass unit for magnesium 24 is 23.99 for magnesium 25 it's 24.99 and for magnesium 26 it's 25.99 those are your amu's and again that allows us to use it so we do not have to use those exponents but magnesium 24 25 and 26 do not exist in equal percent abundances the most common is magnesium 24 so 78.10 of magnesium exists as magnesium 24. 10.13 is magnesium 25 and 11.17 is magnesium 26. so if we look at this percent abundance in a graphical representation you'll find this in your textbook what we'll see is that magnesium 25 excuse me magnesium 24. so 20 uh it has a mass number of 24 12 neutrons exists in 78.10 magnesium 25 exists in 10.13 and magnesium 26 exists at 11.17 so we can see that magnesium 24 has a much higher ratio if we're looking at our bar graph has a much higher ratio magnesium 24 exists in 7.78.10 magnesium 25 and 10.13 and magnesium 26 in 11.7 these are not all equal if they were equal we would look at our bar graph excuse me let me go ahead and delete this y-axis we don't need that if they were this is how magnesium actually exists if it was all equal which magnesium does not exist like this isotopes do not exist like this since there are three isotopes we would expect it to be 33 for each isotope so 24 25 and 26 and what we would see is again if they were all equal magnesium 24 would be in 33 percent magnesium 25 would be in 33 and magnesium 26 would be also in 33 and that would be if all isotopes were equal but we do not see that so that is this is a graphical representation of how magnesium actually exists so when we're calculating the mass of an element we have to take into account these varying percentages and that is what we're talking about when we're talking about the atomic mass which we've learned about two slides ago the that atomic mass is going to be how much an atom weighs and so we need to take into account each of these isotopes each of these different percentages and so we can see that in our graphical representation that each isotope is not equal so it's not just 33 you cannot take each of the masses and average them out um and that is because they're not equal so what we need to do is we need to take in that weighted percentage so we're going to go ahead and look at a different example where we only have two isotopes because that's going to be a little bit easier so we're going to calculate our atomic mass for chlorine and you will get to calculate the atomic mass for magnesium after we look at this chlorine example so you have chlorine 35 and you have chlorine 37 chlorine 35 and chlorine 37. so your atomic mass unit of chlorine 35 is 34.97 and your atomic mass unit for chlorine 37 is 36.97 and you could see if we rounded this up this would be 35 and if we rounded 36.97 up that would be 37. so we don't use decimal places when we're talking about the specific isotope so now we're going to talk about the percent abundance so 34.97 plus 36.97 again it's not necessarily going to be a 50 50 mixture but what we can assume is that we're we need a hundred percent of these two atoms they both have to add up to 100 so chlorine exists in 75.76 and chlorine 37 exists in 24.24 so 75.76 divided by 100 is going to give you your percent contribution to the mass so chlorine 35 is contributing at 75 or 76 which gives you a mass of 26.49 amuse and fluorine 37 is contributing much less a quarter of all the chlorine atoms that exist have chlorine 37 and that is contributing to an atomic mass of 8.962 atomic mass units when you add both of those up you will find that chlorine has an atomic mass unit of 35.45 amuse and this is the number you see on the periodic table that is where the molecular mass comes from of chlorine is because you have chlorine 35 and chlorine number 37 again they're not equal it's not a 50 50 mixture chlorine 35 you have in a percent abundance of 76 while chlorine 37 you have a percent abundance of 25 so chlorine 35 is contributing to 26.49 atomic mass units while chlorine 37 is contributing only 8.962 atomic mass units and so together those are going to equal the number that you'll find on the periodic table the amount that chlorine actually weighs for this calculation this value your percent abundance needs to be given if you don't know the percent abundance you would never be able to calculate the contribution so your percent abundance needs to be given so let's look at this in a graphical diagram so we're again we're looking at chlorine uh chlorine seven or chlorine which has a atomic number of 17. on the periodic table you'll find that chlorine has an atomic mass unit of 35.45 and that's again because chlorine 35 we were just uh told that it contributes 75.76 percent and chlorine 37 is contributing 24.24 so out of that 35.45 75.76 of that is chlorine 35 and out of that 35.45 24. 24 is chlorine 37. again it's not a 50 50 mixture bromine has a 50 50 mixture of the two isotopes chlorine does not so you do need to have that percent abundance given in order to calculate uh in order to calculate the percent contribution towards the molecular mass and you'll have lots of practice of this in the textbook for magnesium and bromine and other elements that have two or more isotopes so again this is going to take practice so let's go ahead and look at four point chapter four or section 4.6 which is electron uh energy levels so 4.6 is electron energy levels it's a lot of slides to depict what's going on here so here's the electromagnetic spectrum there's a wide variety of different waves we have radio waves microwaves infrared rays waves all safe for humans to be exposed to then we have the portion of the visible light spectrum which is very small this is what we can actually see and then you'll have ultraviolet rays which is anything higher than the visible spectrum are actually quite dangerous to ourselves ultraviolet rays which is what the sun radiates um partially and then you'll have medical x-rays and gamma rays and those are all you don't want to be exposed to those those are high energy and uh anything below the visible light spectrum is considered low energy so that is the electromagnetic spectrum so when we think about electrons we want to go ahead and think about electrons can or part of the particles can be existing in different portions so now up until this point we've talked about protons what's going on inside the nucleus so notice that section 4.6 is all about electron energy levels so now we're focusing on what's going on outside the nucleus because we're looking at the electron energy levels so now we're changing gears a little bit and this is again outside the nucleus which we learned in the beginning of this lecture electrons are outside the nucleus so again up until this point we've been focusing on what's going on inside the nucleus now we're thinking about what's going on outside the nucleus so we're going to look at electron energy levels and you can have this thing called the principal quantum number and that is represented as n we are not learning how to calculate this quite yet but your principal quantum number one is the lowest energy and seven is the highest energy and the way that we can think about what's going on is inside the nucleus remember inside the nucleus are your protons and your neutrons so what we're thinking about is we're thinking about electron energy levels and this is outside the nucleus and these can move they can move around and they can change energy levels protons and neutrons are not under most normal circumstances not going to change so right now we're only looking at again we're only looking at electrons and those because they're outside the nucleus they could move around and they can change energy levels so um and we'll look at why that is in a little bit later so right now inside the nucleus nothing is happening inside that nucleus outside the nucleus we can think about this lowest energy level on this bookshelf is being closest to the nucleus it's the lowest in energy then um the next energy level is slightly further away from the nucleus making it slightly higher in energy and then the more uh the further away you get from the nucleus the higher in energy and we'll talk about why that is in one second so the way that you can think about is these electrons that are closest to the nucleus this orange book can jump into the next available spot if there's a spot available for it just like this purple book could jump to the next energy level up if there's space for it in the bookshelf so electrons can move around uh into different energy levels outside the nucleus so let's go ahead and think about again let's go ahead and think about what's going on inside the nucleus we're going to go ahead and look at lithium so inside the nucleus you have three protons so we're looking at lithium outside the nucleus you have two energy levels you have your first energy level and you have your second energy level at this point you do not need to know how many energy levels that will be told to you at this point you eventually will will be able to tell later on um when we get into electron orbital filling which is the next section but right now we're just looking at lithium as two energy levels again you're not expected to know that we have three protons inside the nucleus so therefore we know we're looking at uh lithium with no charge again we are not looking at charged elements at all in this chapter we will get to that in chapter six so right now you can assume that the number of protons has to equal the number of electrons this is not always going to be true but the first two electrons are going to be in the set the first energy level this lowest level closest to the nucleus the second energy level out so this would be n is equal to two and this energy level that's closest to the nucleus is n is equal to one that third electron is a little bit further away from the nucleus and so what we want to think about is we have the first energy level this electron is very close to the nucleus so what's going on is again you have this positive and this negative charge are attracted to one another so that's going to be a lower in energy because the positive and the negative are close to each other so those can balance each other out when you get a little bit further away from the nucleus though so the second energy level that positive charge does it isn't as strongly attracted to that negative charge so that's what makes it higher in energy and so it's a little bit confusing first as a concept because we don't know that energy levels are not created equal and so we need to be told that so that's what this pictorial diagram is explaining to us so you can have changes in the energy level this electron that i have highlighted in this beige color can go to this energy level with um with some help it doesn't just spontaneously do that but it could do that with some actual help you can move electrons into different energy levels and that is going to take energy so what happens is and that's how light uh is is used whether it's visible light or not visible light so if you have your lithium again i'm just using lithium in an example so you have your lithium the electron and you promote that electron to an energy level further away from the nucleus then what you're going to get is higher energy photons are going to be admitted and these are higher in energy so when you're moving an electron from a lower energy level to a higher energy level you have high energy photons are emitted and so these are higher in energy and this would be something like the x-rays or the gamma rays on your electromagnetic spectrum uv rays something like that higher in energy when you have an electron that is being it's still being promoted but it's being promoted to an energy level that's closer to the original state you have lower energy photons are admitted and these are lower in energy so in your let's go ahead and look again at our bookshelf when we have our bookshelf is being promoted all the way let's say to energy level number five that probably wouldn't happen but if that did happen then when the electrons come when the electrons are emitting their energy they're going to be much higher in energy if you have this book right here this uh beige book and you're only promoting it to the next energy level when that electron comes back down and is coming back down into its normal state then you're gonna have a lower energy level um and that is lower in energy something like radio waves and microwaves so again we're promoting an electron from one energy level to another energy level and so if you're promoting an electron that's from let's say n is equal to one to n is equal to two when that electron goes back down to the n is equal to one energy state that's going to be lower in energy from our bookshelf diagram if you are promoting an electron from let's say n is equal to one and you're promoting it to n is equal to five when that electron goes back down to n is equal to one that's going to be something uh more high in energy which is something like an x-ray or a gamma ray and that's what this pictorial diagram is explaining so that's what's happening and how um electrons are it's you know generating energy so inside an orbital you can have subshells and again closer to the nucleus you have one type of subshell a little bit further away from the nucleus you have two subshells three energy uh a principal quantum number so three energy states you have three elect or three types of subshells and when you're four energy levels away from that nucleus you have four types of subshells and we call these s p d and f so those are the types of subshells that you can have you could have an s subshell a p subshell a d sub shell or an f sub shell and these subshells again are not all equal these sub shells are going to have varying shapes so let's go ahead and look at just what an s sub shell will look like so it doesn't matter whether your s is four three two or one all s subshells are going to have this shape so this is an s subshell is always going to be this spherical shape that is an s subshell and again that can be n is equal to one n is equal to two n is equal to three n is equal to 4 and so on and so forth it does not matter all s subshells have this spherical shape if we go back to our subshell diagram we'll notice that p's what we have three slots we have our first slot we have our second slot and our third slot and again it doesn't matter if your it's n is equal to one and is equal to two uh n is equal to two three or four you have three slots all the time all highlighted in green and those are these three slots so you have the first slot for green the second slot in green and the third spot in that green diagram and this can be p is equal to two p is equal excuse me for n is equal to two n is equal to three or n is equal to four it does not matter all of your p sub shells look like this so you have your first box of green you have your second box of green and you have your third box of green on the previous page so you have your first box your second box and your third box of green one of those is representing this orbit this sub shell the second box is representing this sub shell and the third box is representing this subshell and so that is again here's box one box two and box three your d sub shells you have one two three four and five potential subshells and again this only exists and n is equal to three and n is equal to four so if you go back to that book diagram that's only n is equal to 3 and is equal to 4 and n is equal to 5. um so higher energy orbitals uh only have this d option n is equal to 1 or n is equal to two do not have d options so we would expect five different uh subshells so let's go ahead and look at our d's and again we have that highlighted in our tan color so you have your d your first one your second one your third box your fourth box and your fifth box so we don't want to write out these pictures every time you can see they're quite complex to write out so we just write them out as these boxes one two three four and five boxes but one box represents let's just say we're gonna call this box one two three four and five those five boxes are one two three four and five those are all the different d's and then last but not least we have f's represented here in this purple so i'm going to show a this purple subshell is one two three four five six and seven lots of uh subshells and this only exists when n is equal to four or higher so we have one two three four five six and seven and again that is represented as that first box our second box our third box on the previous diagram our fourth box our fifth box our sixth box and our seventh box so why am i showing you this slide these are the varying shapes of what those boxes are representing you do not need to know this okay you do not need to memorize this i don't want you to memorize all of these different shapes what i do want you to memorize or what i do want you to know is that again you do not need to memorize all these different shapes the point of this slide is to actually show what these boxes are representing they're not just arbitrarily given boxes they actually have different shapes so you do not need to memorize all of these different shapes but what you do need to know is that s subshells p subshells d subshells and f subshells all have these different subshells you don't need to know what those subshells actually look like but you do need to know that those sub shells exist so now let's talk about what that actually means with all of these subshells so those are the shapes and this is how orbitals fill so this is 4.7 which is all about electron configuration and this is going to take practice you have your electron configuration and again this is from we can think about this being from the previous slide of the shapes so remember all s subshells it doesn't matter what the n is what the number is so one two three four five six seven all of those have this spherical shape the size of that shape can vary again we're not talking about that we're not talking about the sizes of these but all s subshells have this spherical shape and in that spherical shape you can have two electrons can fit in there and so you'll have this is one electron and you'll have your second electron represented as this half arrow is represents one electron and we can see that they're opposite of one another um this first electron is where you have half of the arrow pointing up and your second electron is where you have the other half pointing down but each represent one electron and you don't need to know what that represents but you do want to show that one is up and one half arrow is down that's what this symbol is showing so each of these boxes can hold two electrons so a grand total of two electrons so each box holds two electrons max okay so each box will have two elec whole be able to hold two electrons maximum this is one representation of electron configuration or how orbitals fill how some shells fill to me this is kind of complicated i like it's the exact same diagram or it looks a little bit different but it's telling us the exact same thing i like this one a lot better so again you still have your n is equal to 1 2 3 4 5 6 7 8 so on and so forth but on this diagram it's much easier because you will be able to follow what is uh going on and i'm going to choose a gray highlighter you'll be able to follow what is going on with regards to the arrows so all you have to do is you're gonna and we haven't seen an example yet but we're just learning how to read this table where we learn how to read this diagram so we're gonna when we do start filling we're gonna fill our one subshell burst and then you'll follow the arrow and then you fill your 2s subshell you follow this arrow you you fill your 2p subshell and so on and so forth so you're going to follow the arrow all the way along when we start filling electrons the same thing is true here you're going to fill in your 1s first and then your 2s and then that goes to filling in your 2p and then your 3s so it doesn't matter which diagram you like to use for filling electrons your electron configuration you can use this diagram or you can use the one that i have in this handout which is this diagram it doesn't matter whichever one you want to use and i will allow you to use these for the homework and the exams so you don't need to memorize that for this class but you will for future chemistry classes but for this class since we're just learning the basics you can use this table don't use both tables use either this table on this diagram whichever one you feel more comfortable with or use the table from the text it doesn't matter whichever one you choose to use so let's go ahead and look at an example of this would be boron boron is number five on the periodic table your 1s orbital can hold two electrons so i'm going to represent one electron and my second electron we know boron is number five on the periodic table we have five electrons again we're no longer talking about what's going on inside the nucleus we're talking about what's going on outside the nucleus but boron has five protons therefore we also know it has five electrons because we have not talked about any charged species yet so the first orbital that gets filled is 1s the second orbital that gets filled is going to be 2s and again 2 electrons can fit in that box the next orbital that or a subshell that gets filled is 2p so we're going to go ahead and put our 2p here we need a gram total of 5 electrons currently we have one electron two electrons we have three electrons four electrons and now we need to put our fifth electron in that two p sub shell the problem with this diagram is again it doesn't tell you how many squats you have so you need to remember that you have three slots for a p if you want to use this diagram no problem here are those three slots so if we're looking again at boron we have one electron i'm going to go ahead and erase this we have a single electron and it's going to pair up for the 1s your second and third or excuse me your third and fourth electron are going to go in the 2s energy and then your fifth electron is going to go into that first slot so again you can use whichever diagram you feel more comfortable using this diagram has each slot available for you this diagram i like the arrows it tells you how to follow the diagram but you have to remember that a p has three slots you have to remember a d has one two three four five slots and you have to remember an f has one two three four five six seven slots um if you're using this table you can choose however you want to use again whichever table you like again we are not talking about any other element except for neutral elements so the number of protons equals the number of electrons we will learn about um charges later on so let's go ahead and look at the electron configuration we're going to look at four different examples and you can have this table out for you so we're going to look at 4.57 which is right the complete the electron configurations for neutral atoms again we are still not talking about charged atoms so if we look at boron which we just did oops excuse me we're looking at problem a which is boron boron on the periodic table is number five so we know that it has five protons again we're not talking about any charged species so therefore we know it has 5 electrons so 1s always gets filled first followed by 2s and then 2p so we have 5 electrons that we need to take into account so that's 1 2 3 four and five electrons and when we write out this electron configuration we can either write this out as one s and then two and two s two and two p one so what we're saying is one s one or excuse me one s is holding two electrons so your one s subshell is holding these two electrons your two s is holding these two electrons and that's what this subshell is saying that your 2s is holding those two electrons and then because you're at number five on the periodic table your 2p can hold up to six electrons but you only have one in there so your 2p is holding one electron if we add this up and find what we will find is that 2 plus from the 1s subshell plus 2 from the 2s subshell plus that 1p is equal to 5. 2 plus 2 is e plus 1 is equal to 5. and that is the same number of electrons that we have for boron the other way that you can write this shorthand is that you will have helium and then you'll have 2s2 and 2p1 so this is the shorthand and we'll learn about this uh later on as well i'll talk about this when we look at our next example which is sodium i'll talk about how you use that shorthand so let's go ahead and look at b which is sodium which is number 11 on the periodic table so we're going to go ahead and fill our 1s and then our 2s and then our 2p and then our 1s and again you can't excuse me our 3s let me go ahead and fix that really quickly our 3s i know this by heart but again we're filling the 1s followed by we're following this arrow down to the 2s followed by the 2p and then following the 3s so that's where these numbers are coming from and again you will need to use this table until you get the hang of it so sodium is number 11 on the periodic table that means you have 11 protons and therefore again we're only talking about neutral elements so you have 11 electrons so our first two electrons go in the 1s subshell so that's the first two and then electrons 3 and 4 are going in the 2s subshell 5 6 7 8 9 10 go in the 2p and 11 goes in the 3s so you can either write this as 1 s2 2s2 2p6 and 3s1 if you add up all of your exponents you have 2 plus two is four plus six is ten plus one is equal to eleven which is how many electrons we have or you can write this as neon and then three s one so where is this shorthand coming from let's actually look at the electron configuration for neon which is the second noble gas so neon is number 10 on the periodic table so that means that you have 10 protons because your protons is equal to your number of electrons you have 10 protons so that must mean that you have 10 electrons so again i'm going to go ahead and instead of writing it horizontal i'm going to go or excuse me vertical i'm going to write it horizontal it doesn't matter which this shows that the energy levels are not equal but you will most often see it written horizontal so you have 1s 2s 2p 3s so again we're looking at neon 10 electrons on uh 10 protons 10 electrons so you have electron 1 and electron two electron three electron four electron five six seven eight nine and ten and so there's nothing in this s which is fine there doesn't need to be you have ten protons and ten electrons because neon is a noble gas and we'll talk about the stability of this in chapter 6. um we can write this shorthand as 1s2 2s2 and 2p6 so that would be 1s2 2s2 2p6 or we would just write this as neon and so the shorthand is only for noble gases so when you're using the shorthand this must be a noble gas this must be for your shorthand this has to be a noble gas and again we'll get into that more in chapter six but for now if you are getting help online for writing electron configurations to help your answer you may see it and you will most often see it written in the shorthand and that's what that means it's the closest noble gas so again i'll go over that in more detail in chapter six but i did want to expose you to that now in case if you are using something um like uh the internet to help you with your homework so let's go ahead and look at lithium which happens to be number three on the periodic table so you're going to have your 1s and your 2s that's all that will be used those are the only subshells so lithium has the first two electrons are in the one s subshell and your third electron is in the 2s subshell this electron configuration would be written as 1s2 and 2s1 or helium in brackets 2s1 let's go ahead and look at um d is magnesium i'll have you work on that one on your own let's go ahead and look at um carbon so we're going to look at carbon carbon is number six on the periodic table so you have six protons and therefore you have six electrons so it's going to have an electron subshells of 1s 2s and then 2p so what happens we're looking at six electrons so you have your first two electrons are in the first subshell your third and fourth electron are in the second subshell then your fifth electron goes in the first subshell and your sixth electron goes in subshell 2p the second one you do not for carbon you do not go 1s 2s and then 2p you do not put you still put your first two electrons in subshell one you put your second two electrons in subshell or your third and fourth electrons in subshell two however you do not pair the electrons up in subshell that third that two p subshell these two electrons do not want to be paired and that again is because remember electrons have um the same charge so this is your electrons the two electrons are going to repel one another so if and when possible your electrons want to be spread out so they want to be closer to the nucleus and they're going to pair up first if possible the further away you get from the nucleus the more energy is required um so which is no problem but if and when possible they want to spread out so it's not always going to be the case you definitely feel your subshells paired up first but then when they can be unpaired you do unpair them and so that is the correct way of writing carbon this uh on the right hand side of the screen is the incorrect way of writing carbon you do not pair up those two electrons if you do not have to so that's how you fill the energy diagrams the electron configuration energy diagrams so again you'll have a lot of practice so now let's go ahead and talk about lewis dot structures or periodic trends so you'll have lots of practice with your electron configurations so 4.8 is all about trends on the periodic table and these trends on the periodic table is all about valence electrons and again we having outside um this is the valence electrons our electrons after the noble gas in your electron configuration so let's again look at carbon carbon is number six on the periodic table um you have your 1s you have your 2s and you have your 2p when you're writing your electron configuration that is going to look like that your 1s this is the electron configuration of helium this whole thing would be the electron configuration of neon but we can see that this is not fully filled so your electron configuration does not represent neon if you were to write carbon shorthand then that would be helium in brackets and then you have your two s two two p ah two two s two two p two so your valence electrons are these electrons outside that noble gas when you're shorthand configuration so these are your valence electrons and you have four of them you have two electrons and the two s2 and two electrons and the 2p2 for your valence electrons so that's what we're talking about that is the definition of the valence electrons the electrons that are closest to the nucleus those are core electrons and nothing happens with those under any circumstance the core electrons nothing's gonna happen to those your valence electrons is where chemistry can actually happen i mean those are the electrons again outside of that noble gas configuration and we'll talk about that in more detail in chapter six so when we're talking about trends on the periodic table we can look at the way that the periodic table is set up so you have your periodic table and this is set up such like this here are your transition metals we're not really focusing on that section of the periodic table but what we'll notice is that this is abbreviated as column 1a 2a and then you have 3a 4a 5a you don't have to worry about six a and b uh or a and b you can either think about the a's or just ignore the a and the b abbreviation this would be your these are your b's and your a's are up here so you can ignore those so the way that valence electrons are set up in column one or one a all of those elements have one valent electron in column 2a all of these elements have two valence electrons and column 3a all of these electrons have three valence or all of those elements have three valence electrons and that is why um column four a has four valence electrons column 5 a has 5 valence electrons column 6a let's go ahead and write column 6a as we'll go ahead and use this pink color oops i already used pink so we'll go ahead and use more of a bright red color column 6 a has six valence electrons column seven a again we're not in focusing on the transition metals at all column seven has seven valence electrons and last but not least column eight has no valence electrons because those are all noble gases again we're not focusing on the transition metal portion of the periodic table at all all of column one has one valence electron so here we're looking at valence electrons and remember from the beginning of the lecture we discussed the importance of groups or columns sharing chemical properties they share valent electrons so all of column one has one valence electron all of column two has two valence electrons all of column three has three valence electrons and so on and so forth and that is so your valence electrons are is the same as your column number and that is how those column numbers got their numbers in the first place is they happen to go in numerical order but they also happen to have that many number of valence electrons and again the valence electrons is where the chemistry actually happens so those that's how the periodic table one way that the periodic table is set up that's one trend in the periodic table and we call this another way of writing or drawing this is uh or another way of depicting this is called lewis dots and again we'll get more into detail of all of these types of things in chapter six lewis dots is all based on your column number or your group number so it represents your number of valence electrons so let's look at magnesium magnesium is in column two on the periodic table and so it has two valence electrons so you put a dot to the right and a dot to the left of the element you can do it a dot above and below it doesn't matter you typically do not write magnesium with two electrons uh paired up together if they are not if they don't want to be paired they don't have to be paired let's go ahead and look at carbon carbon is in column four so it has four valence electrons so i have one two three and four valence electrons again this is the exact same depiction of saying okay these are my valent electrons those are outside the core of that uh the core electrons so another way writing lewis dots is another way of writing your electron configuration of all of your valence electrons so again we break these sub these topics up into different sections but they're all extremely important in bringing the whole picture together of what's actually going on so let's look at oxygen it's in column 6 of the periodic table carbon is in column 4. let's go ahead and complete that so oxygen is in column 6 of the periodic table so i'm going to go one two three four now i have no choice but to pair so i'm gonna pair five and pair six it doesn't matter which you pair together you compare any ones that you want let's go ahead and look at helium helium is in column eight there is no valence electrons so we're going to go ahead and look at sorry neon let's look at neon neon is one we're looking at neon not helium one two three four five six seven and eight they all have to be paired so we have no valent electrons because they all happen to be paired but you can still show that it's in column eight so the way that the periodic table is set up is that you'll have lewis symbols in periods one to four so we're looking in rows one to four so your lewis symbol for all of your 1a's are going to have one dot hydrogen lithium sodium potassium again we're looking at the row but we're also looking at the period and the group so all of column twos beryllium magnesium calcium are going to have two dots and you can see that they have their dots not paired but that they have them above and to the right it doesn't matter how you show your dots you can show them any which way of group 3a all of column 3a it doesn't matter which row you're in uh boron aluminum gallium indium all of those are going to have three dots all of four a's it doesn't matter which row is carbon silicon germanium are all gonna have four dots so that is uh table four point eleven and that again is a trend on the periodic table we can look at the atomic size of a trend of the periodic table so rubidium has the largest atomic size and helium actually has the smallest atomic size and so as you go to the right of the periodic table your atomic size is decreasing and as you go down uh column your atomic size is increasing and so let's go ahead and think about what's going on inside that nucleus the more protons that you have the larger that nucleus is going to become and the more orbitals that you are going to need to have or the more subshells you are going to need to have outside of the nucleus so the more protons is also going to affect the number of subshells that you have um but why are we decreasing as we're as we're going from left to right on the periodic table that's because the number of protons and the number of electrons the number of protons can help uh pull the orbitals closer to one another so rubidium is going to have the largest even though it may not necessarily have the largest number of protons um and that is again it's all a balance of the number of subshells you have versus the number of protons that you have uh inside the nucleus so this is the overall trend of atomic size here we have the atomic excuse me the overall trend of ionization energy we'll get into more definition for this in chapter six but we're just learning on what the actual trend is so ionization energy is the amount of energy to remove a single electron and that's really important it's a see how much energy it takes to remove and a single electron and so we'll look again at electron configurations and see why we're talking specifically about one specific single electron the overall trend that you need to know right now is that that ionization energy the amount of energy it takes to remove one electron is going to increase as we go from right to left across a row and it's also going to increase as we go down the column it's going to take more energy to remove a single electron as you go down the periodic table excuse me it's going to take it decreases as you go down the column and it increases as you go across the row and so we will see uh why that is again when we're talking about moving these electrons around and we're actually talking about chemical reactions which we still have not got to yet we'll get there in chapter six and then this is in the overall trend for metallic character so as you go across a row your metallic character decreases and as you go down a column your metallic character increases so how um how much does your atom behave like a medal that is that trend so again you will these are just the definitions in chapter six we're going to get into more of these trends in much more extensive detail so just to summarize what we learned today that we learned a lot this is a heavy duty chapter i would suggest really taking your time with this chapter this chapter really lays the fundamentals for the rest of your chemistry careers so in section 4.1 we talked about elements and symbols on the periodic table that's the first thing we talked about section 4.2 we talked about the periodic table and how it's set up in section 4.3 we talked about the atom and what it means to be an atom dalton's theory specifically we had those four points in section 4.4 we talked about atomic number and mass number atomic number is the number of protons and we talked about the mass number which is your number of protons plus the number of neutrons that's what we learned in section 4.4 in section 4.5 what we discussed was isotopes which is a varying number of neutrons so we didn't change anything with regards to your proton count or your electron count we only varied the number of neutrons and we learned how to calculate the percent ratio of the neutrons and how those contributed to the overall mass and 4.6 this is where things started to pick up and get um uh where where we really need to think about um electrons electron configuration things like that very fundamental portion of chemistry this is your electron energy levels and this again is where we started thinking about things being outside of the nucleus 4.7 we looked at our electron configuration again only of neutral elements we will talk about um elements that where we lose or gain an electron later on so we will talked about electron configuration and we talked about how you fill those subshells and then in section 4.8 last but not least we talked about periodic trends so how can we put that information that we learned in section 4.6 and 4.7 how can we put that in the trend of the periodic table so that is chapter four you will have lots and lots of practice if any of this is confusing please do not hesitate to come see me in office hours i would be more than willing to help of course and also it's going to take lots and lots of practice for this really to solidify and sink in so please take your time with the homework and make sure that you fully understand it because again this is a very fundamental chapter for the rest of your chemistry careers