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Let's figure out the electron configuration for nickel,

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right there.

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28 electrons.

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We just have to figure out what shells

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and orbitals they go in.

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28 electrons.

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So the way we've learned to do it is,

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we defined this as the s-block.

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And we can just remember that helium actually belongs here

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when we talk about orbitals in the s-block.

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This is the d-block.

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This is the p-block.

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And so we could start with the lowest energy electrons.

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We could either work forward or work backwards.

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If we work forwards, first we fill up

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the first two electrons going to 1s2.

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So remember we're doing nickel.

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So we fill up 1s2 first with two electrons.

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Then we go to 2s2.

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And remember this little small superscript 2 just means

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we're putting two electrons into that subshell

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or into that orbital.

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Actually, let me do each shell in a different color.

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So 2s2.

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Then we fill out 2p6.

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We fill out all of these, right there.

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So 2p6.

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Let's see, so far we've filled out 10 electrons.

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We've configured 10. You can do it that way.

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Now we're on the third shell. The third shell.

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So now we go to 3s2.

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Remember, we're dealing with nickel,

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so we go to 3s2.

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Then we fill out in the third shell the p orbital.

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So 3p6.

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We're in the third period, so that's 3p6, right there.

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There's six of them.

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And then we go to the fourth shell.

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I'll do it in yellow.

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So we do 4s2. 4s2.

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And now we're in the d-block.

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And so we're filling in one, two, three, four,

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five, six, seven, eight in this d-block.

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So it's going to say d8.

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And remember, it's not going to be 4d8.

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We're going to go and backfill the third shell.

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So it will be 3d8.

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So we could write 3d8 here.

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So this is the order in which we fill,

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from lowest energy state electrons to highest energy state.

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But notice the highest energy state electrons,

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which are these that we filled in, in the end,

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these eight, these went into the third shell.

54
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So when you're filling the d-block,

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you take the period that you're in minus one.

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So we were in the fourth period in the periodic table,

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but we subtracted one, right?

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This is 4 minus 1.

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So this is the electron configuration for nickel.

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And of course if we remember,

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if we care about the valence electrons,

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which electrons are in the outermost shell,

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then you would look at these right here.

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These are the electrons that will react,

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although these are in a higher energy state.

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And these react because they're the furthest.

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Or at least, the way I visualize them is that

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they have a higher probability of being further

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from the nucleus than these right here.

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Now, another way to figure out

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the electron configuration for nickel--

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and this is covered in some chemistry classes,

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although I like the way we just did it

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because you look at the periodic table

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and you gain a familiarity with it,

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which is important, because then

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you'll start having an intuition

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for how different elements react with each other

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-- is to just say, oK, nickel has 28 electrons,

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if it's neutral. It has 28 electrons,

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because that's the same number of protons, which is the atomic number.

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Remember, 28 just tells you how many protons there are.

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This is the number of protons.

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We're assuming it's neutral.

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So it has the same number of electrons.

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That's not always going to be the case.

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But when you do these electron configurations,

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that tends to be the case.

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So if we say nickel has 28, has an atomic number of 28,

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so it's electron configuration we can do it this way, too.

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We can write the energy shells.

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So one, two, three, four.

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And then on the top we write s, p, d.

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Well we're not going to get to f.

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But you could write f and g and h and keep going.

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What's going to happen is you're going to fill this one first,

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then you're going to fill this one, then that one,

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then this one, then this one.

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Let me actually draw it.

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So what you do is, these are the shells that exist, period.

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These are the shells that exist, in green.

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What I'm drawing now isn't the order that you fill them.

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This is just, they exist. So there is a 3d subshell.

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There's not a 3f subshell.

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There is a 4f subshell.

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Let me draw a line here,

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just so it becomes a little bit neater.

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And the way you fill them is you make these diagonals.

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So first you fill this s shell like that,

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then you fill this one like that.

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Then you do this diagonal down like that.

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Then you do this diagonal down like that.

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And then this diagonal down like that.

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And you just have to know that there's only two can fit in s,

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six in p, in this case, 10 in d.

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And we can worry about f in the future,

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but if you look at the f-block on a periodic table,

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you know how many there are in f.

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So you fill it like that.

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So first you just say, OK.

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For nickel, 28 electrons.

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So first I fill this one out.

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So that's 1s2. 1s2.

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Then I go, there's no 1p, so then I go to 2s2.

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Let me do this in a different color.

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So then I go right here, 2s2.

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That's that right there.

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Then I go up to this diagonal, and I come back down.

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And then there's 2p6.

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And you have to keep track of how many electrons

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you're dealing with, in this case.

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So we're up to 10 now.

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So we used that one up.

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Then the arrow tells us to go down here,

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so now we do the third energy shell.

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So 3s2.

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And then where do we go next?

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3s2.

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Then we follow the arrow.

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We start there, there's nothing there,

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there's something here.

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So we go to 3p6.

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And then the next thing we fill out is 4s2.

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So then we go to 4s2.

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And then what's the very next thing we fill out?

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We have to go back to the top.

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We come here and then we fill out 3d.

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And then how many electrons do we have left to fill out?

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So we're going to be in 3d. So 3d.

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And how many have we used so far?

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2 plus 2 is 4.

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4 plus 6 is 10.

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10 plus 2 is 12.

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18.

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20.

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We've used 20, so we have 8 more electrons to configure.

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And the 3d subshell can fit the 8 we need,

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so we have 3d8.

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And there you go, you've got the exact same answer that

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we had when we used the first method.

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Now I like the first method

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because you're looking at the periodic table the whole time,

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so you kind of understand an intuition

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of where all the elements are.

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And you also don't have to keep remembering,

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OK, how many have I used up as I filled the shells? Right?

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Here you have to say, i used two, then I used two more.

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And you have to draw this kind of elaborate diagram.

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Here you can just use the periodic table.

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And the important thing is you can work backwards.

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Here there's no way of just eyeballing this and saying,

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OK, our most energetic electrons are going to be

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3d8,

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and our highest energy shell is going to be 4s2.

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There's no way you could get that out of this

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without going through this fairly involved process.

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But when do you use this method, you can immediately say,

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OK, if I'm worried about element Zr, right here.

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If I'm worried about element Zr.

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I could go through the whole exercise of

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filling out the entire electron configuration.

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But usually the highest shell, or the highest energy electrons,

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are the ones that matter the most.

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So you immediately say, OK,

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I'm filling in 2 d there,

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but remember, d, you go one period below.

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So this is 4d2.

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Right? Because the period is five.

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So you say, 4d2. 4d2.

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And then, before that, you filled out the 5s2 electrons.

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The 5s2 electrons. And then you could keep going backwards.

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And you filled out the 4p6. 4p6.

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And then, before you filled out the 4p6.

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then you had 10 in the d here.

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But what is that?

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It's in the fourth period,

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but d you subtract one from it, so this is 3d10.

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So 3d10.

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And then you had 4s2.

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This is getting messy. Let me just write that.

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So you have 4d2.

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That's those two there.

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Then you have 5s2. 5s2.

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Then we had 4p6.

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That's over here.

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Then we had 3d10.

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Remember, 4 minus 1, so 3d10.

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And then you had 4s2.

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And you just keep going backwards like that.

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But what's nice about going backwards is you immediately know,

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00:09:08,890 --> 00:09:11,160
OK, what electrons are in my highest energy shell?

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00:09:11,180 --> 00:09:14,240
Well I have this five as the highest energy shell I'm at.

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00:09:14,260 --> 00:09:17,450
And these two that I filled right there, those are

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00:09:17,470 --> 00:09:20,660
actually the electrons in the highest energy shell.

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00:09:20,680 --> 00:09:23,240
They're not the highest energy electrons. These are.

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00:09:23,250 --> 00:09:24,680
But these are kind of the ones that have

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the highest probability of being furthest away from the nucleus.

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00:09:28,090 --> 00:09:29,950
So these are the ones that are going to react.

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00:09:29,960 --> 00:09:31,450
And these are the ones that matter

220
00:09:31,470 --> 00:09:33,100
for most chemistry purposes.

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00:09:33,110 --> 00:09:35,180
And just a little touchpoint here,

222
00:09:35,260 --> 00:09:36,710
and this isn't covered a lot,

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00:09:36,730 --> 00:09:39,780
but we like to think that electrons are filling these buckets,

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and they stay in these buckets.

225
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But once you fill up an atom with electrons,

226
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they're not just staying in this nice, well-behaved way.

227
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They're all jumping between orbitals,

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and mixing together,

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and doing all sorts of crazy, unpredictable things.

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But this method is what allows us to at least get a sense

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00:09:54,750 --> 00:09:56,640
of what's happening in the electron.

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For most purposes, they do tend to

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react or behave in ways

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that these orbitals kind of stay to themselves.

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But anyway, the main point of here is really just to

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teach you how to do electron configurations,

237
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because that's really useful for later on

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knowing how things will interact.

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And what's especially useful is to know

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what electrons are in the outermost shell,

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or what are the valence electrons.