in the next couple minutes we're going to talk a lot about electrons first we're going to start out looking at an atom and looking at the spaces in an atom where electrons can live then we'll learn about the most important type of electrons in an atom these are called the valence electrons we'll learn how you can figure out how many valence electrons and atom has by looking at where that atom is on the periodic table and finally we'll look at how you can take an atom and draw one of these electron dot diagrams for it that shows how many electrons it has so let's get started okay so check out this diagram of an atom I have here in the middle is the nucleus with protons and neutrons and I look at all of these little circles each one of these circles represents a spot that could hold one electron you can think of these as like parking spots for electrons or like theater seats for electrons and these spots for electrons are organized into these circles these circles are called energy levels or shells you can think of these energy levels or shells sort of like they show the paths that the electrons would take as they're spinning around the nucleus here but also energy levels our shells arrange electrons into different groups that are varying distances from the center of the end okay like so for this first group this first energy level or shell can hold two electrons really close to the nucleus moving out a little bit we get to another shell that can hold eight electrons and they're spinning out here and then even further out we have another group that can hold eight electrons now it keeps going from here and there are more and more energy levels or shells but it gets a little bit tricky so I just wanted to focus on these first three to give you an idea of how they work now if you've learned a little bit about atoms already you might know that the have drawn this here this isn't the most perfectly accurate way to represent electrons and atoms but you know what it doesn't matter for our purposes right now we just want to learn the basics drawing and thinking about atoms like this is totally fine so don't worry that it's not super accurate okay so let's look at what happens when we start filling these electrons parking spaces when we start filling them with actual electrons so we're going to use the periodic table for this will go column by column and here's what I'm doing I've made this big version of a periodic table and you can see it looks a little bit different than the real version of a periodic table okay look at this whole thing in the middle this is sort of a big real periodic table we're not going to worry about any of these elements in here in the middle so this whole section I've put it here just gotten rid of it we're not going to worry about it we're only going to focus on eight columns we're going to focus on these two right here which I've drawn they're skipping everything in the middle and then we're going to focus on these six over here so don't get confused by the way I've drawn this we're just leaving out some of the elements that we don't want to get into right now okay so let's take the first element right here hydrogen now how many electrons are there in hydrogen okay well what we got to do is we got to look it up on the periodic table and we're going to find something like this now the periodic table it doesn't actually tell us how many electrons are in Hajj it's got this one here but that refers to the number of protons so there's one proton in hydrogen that's what its atomic number is now if we assume though that this hydrogen atom if we assume that it doesn't have a charge then the number of electrons is going to equal the number of protons so hydrogen always has one proton but if the atom is neutral if it doesn't have a charge it will also have one electron so let's go back to this diagram of the atom here let's just start with this first energy level okay here's a drawing just the first energy level let's put a nucleus in here I'm not actually going to draw the protons and neutrons instead I'm going to write the number of protons okay so this has one proton and P+ is the abbreviation for protons so 1p plus in the nucleus now here are the two spots in this first energy level where electrons can live there is one electron in hydrogen so we're going to fill that in that was really easy right so we got this first energy level in hydrogen one of the spots is still empty and one of the spots is full okay let's move down here to lithium now if we look up lithium on the periodic table we're going to see this 3 which means that every lithium atom has 3 protons in it but if that lithium atom is neutral which we always assume that it is when we're doing this sort of thing this lithium atom also has 3 electrons so we'll start here will be first concerned with this this energy level that's right here the first one here I'm going to put a nucleus in here 3 plus because there 3 protons in here okay so there are 3 electrons so this one is going to get filled and this one is going to get filled and now we're going to go out want to go to the next energy level okay now that starts getting filled so now it's going to look like this now we want to start thinking about the second energy level the first one is filled and now one electron is going to go here in the second energy level okay so these energy levels they're really like parking spaces imagine that the nucleus is a mall right it's like the parking space is closest to the entrance of the mall those are the ones that fill up first and then as more and more people Park the empty parking spaces move further and further and further away from the center of the mall it's exactly the same way with atoms okay the first energy levels close to the nucleus those are the ones that are going to fill up and then after they're full the other energy levels further out they're going to begin to fill up too okay now let's look at sodium sodium has 11 protons in its nucleus 11 P plus and we're going to assume that since it's neutral we're assuming that it's neutral it has the same number of electrons as protons so let's start filling them in one two in the first energy level now that's full so we're going to start filling the second energy level three four five six seven eight nine ten and finally these are all full but we still have more electrons so now we're going to have to bump it to the third energy level here's a third energy level that we can start filling in ten of these are already living in the atom so we're going to add one more and now there's one in this third energy level okay now check this out because this is important hydrogen lithium and sodium they all have different numbers of electrons but there's a pattern here check this out each one of these atoms has one electron in the outermost shell okay this one's full this one's full but then there's just one here this one's full and then there's just one here and then hydrogen here only has one energy level and it just has one electron in these electrons one one and one these are the valence electrons the most important electrons in an atom we'll talk more about that later why they're so important but all you have to know for right now is that the valence electrons are the electrons in the energy level that is the furthest out from the nucleus so in this atom the valence energy level is the third and it has one electron and here the valence energy level this the furthest out is the second and here the furthest out of the valence energy level is the first so there is a pattern each one of these atoms has one valence electron that's true not just for these first three atoms but for every one of the atoms that's in this first column in the periodic table I didn't want to do the electron structures for all of these others but just trust me that they all have one electron okay so now there's a way that we want to be able to write that to show that these elements have one valence electron and what we can do is draw what we call these electron dot diagrams they're sometimes known as Lewis diagrams where we take the element and then put one dot over it to show that it has one valence electron here's how we'd write the electron dot diagrams for all the elements that are in this column as an example I'll just take lithium and write it here so every single atom in this column has one valence electron okay let's move on and take a look at some of the other columns on the periodic table okay so if everything here has one valence electron let's take a look at this call starting with beryllium beryllium has four protons if it's electrically neutral it's going to have four electrons as well so let's look at how this fills in we've got four protons here in the nucleus and now we're going to go one two in the first energy level and in the second energy level three four okay so we've got two electrons in the outer energy level and look at the wave fill them in I didn't just fill them in clockwise here but one went on the top and then one went on the bottom okay now magnesium magnesium here has an atomic number of 12 so 12 protons and 12 electrons if we assume that it is electrically neutral 12 P Plus here so 12 1 2 3 4 5 6 7 8 9 10 11 12 so what's the pattern here for this second column in the periodic table we've got two valence electrons for magnesium in the third energy level and we have two valence electrons for beryllium in the second energy level so everything in this column has two valence electrons in this outermost shell so we can do is we can draw electron diagrams for everything in the second shell here I'm sorry for everything in the second column here and it looks like this we take the element symbol and then we put a dot at the top and a dot at the bottom and that's how we represent the electrons for here so I'll just do like B e beryllium for example do B e dot on the top dot on the bottom let's go on okay you're probably getting the hang of this so we're going to start moving a little bit faster let's move on to boron here here's boron this is the structure of boron and then here is aluminum down here 13 I'm sorry five protons 13 protons and look at what the structure of the valence electrons is here we've got one two three in the valence shell of boron and for aluminum we've got one two three in the valence shell the same is true for these guys here even though I haven't drawn them out so if in your if you're in this column you have three valence electrons an example of this would be boron and look at how I do the dots for boron okay I do a dot on the top just like lithium I do a dot on the bottom just like beryllium and then I do a dot here to the left to show that these all have three valence electrons and it would be the same way for any of the elements in this column here okay let's do all of these as a group okay this column first has carbon and silicon in each of these have one two three four one two three four valence electrons in their outer shell okay so I can take this and do a dot up here a dot down here a dot to the left and then a dot to the right to show that everything in this column has for us R for its electrons now moving on to the right we've got this column with nitrogen and phosphorus and all these others and everything here has one two three four five one two three four five valence electrons so if nitrogen is my example I'm going to do n dot on the top down on the bottom left right and now I start doubling up so now they're going to be two dots on the top of nitrogen to show that there are these five valence electrons for everything that's in this column you can probably see that there's a pattern that's developing here oxygen and sulfur each have you can count them six valence electrons so I'll take oxygen as an example now look at what I do here for drawing the valence electrons because it gets a little bit tricky you'll figure out that it's a little bit tricky okay dot on the top so anyway six valence electrons for everything in this column oxygen is the example dot on the top dot on the bottom dot on the Left dot on the right now we double up the one on the top and then we double up the one on the right okay so we don't put it on the bottom we put it on the right so up down left right and then around clockwise finally for this column which has at the top of it fluorine and chlorine both of these have seven valence electrons which means that this valence shell is almost full except for one hole in it so I'll take fluorine as mine example here dot on the top dot on the bottom dot on the left dot on the right now we double up double up on the top to up here double up on the right two there and then double up on the bottom so I've only got one guy here on the left that doesn't have a pair now here's the last column that we're going to talk about okay look at what happens here well look at helium neon and argon okay here's helium here's neon and here is argon notice that argon has eight valence electrons doesn't have any empty holes in its valence shell neon also has eight valence electrons but helium only has two valence electrons okay so what's going on in this column is that most of these have eight neon has a argon has a as do Krypton xenon and radon but then there's helium that only has two but regardless of whether you have to I mean of whether you have eight or whether you have two if you're in this column your valence shell is totally full okay so here it's full with eight here it's full with eight and here it's full with two but they're all full and there aren't any empty holes in the shells so as an example I'm going to use neon which has eight so one two three four and now we go clockwise five six seven eight eight valence electrons for most of these guys but remember that helium only has two valence electrons but that all of them have valence shells that are totally full with no empty spots so this kind of sums up everything that we talked about every atom in this column has one valence electron every atom in this column has two valence electrons and then we skip over this middle section and we get three four five six seven and eight so if you know which of these columns a particular atom is in you can figure out how many valence electrons it has