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  • - [Instructor] In a previous video,

  • we've introduced ourselves

  • to the idea of an orbital,

  • that electrons don't just orbit a nucleus

  • the way that a planet might orbit a star,

  • but really, in order to describe

  • where an electron is at any given point in time,

  • we're really thinking about probabilities,

  • where it's more likely to be found

  • and less likely to be found.

  • And an orbital is a description of that,

  • where is it more or less likely to be found.

  • And this diagram shows us the types of orbitals

  • which can be found in the various subshells

  • which are found in the various shells.

  • So you have the s subshell,

  • the p subshell that has three different orbitals in it,

  • you have the d subshell that has one, two, three,

  • four, five different orbitals in it.

  • And then you have the f subshells.

  • Now each orbital can fit two electrons.

  • So if you're thinking about the subshell,

  • the s subshell could fit two electrons,

  • the p subshell can fit six electrons,

  • the d subshell can fit 10 electrons,

  • and the f subshell can fit 14 electrons,

  • two per orbital.

  • Now the goal of this video is to think

  • about electron configurations for particular atoms.

  • And to help us with that, we will look

  • at a periodic table of elements.

  • And so first, let's just think

  • about the electron configuration of the simplest element.

  • If we're talking about a neutral hydrogen atom,

  • a neutral hydrogen atom, it has an atomic number of one

  • which tells us it has one proton,

  • and if it's neutral, that means it has one electron.

  • Now where would that one electron be?

  • Well it would be in the lowest energy level

  • or the first shell, and that first shell

  • has only one subshell in it.

  • It only has one type of orbital.

  • It only has an s subshell, and so that one electron

  • in that neutral hydrogen atom would go over there.

  • So we would say its electron configuration 1s1,

  • in the first shell which is made only

  • of an s subshell, it has one electron.

  • Now what happens if we go to helium?

  • Well, a neutral helium atom

  • is going to have two electrons.

  • So instead of just having one electron in that first shell,

  • we can fit up to two there.

  • So its electron configuration would be 1s2.

  • Now what do you think is going to happen

  • when we go to lithium?

  • Well lithium, a neutral lithium

  • will have three electrons in it,

  • so the first two could go to the first energy level,

  • the first shell, so the first two will go 1s2,

  • and then the third electron is going

  • to go into the second shell,

  • and the subshell that it's going to fill first

  • is the s subshell.

  • So then it'll go to the second shell

  • and start filling up the s subshell.

  • So notice, two electrons in the first shell

  • and one electron in the second shell.

  • Now what about beryllium?

  • Well, that's gonna look a lot like lithium

  • but now it has four electrons.

  • So two of them are going to go into the first shell, 1s2,

  • and then the next two are going to fill up the s subshell

  • in the second shell.

  • I know it's a bit of a mouthful, 2s2.

  • Notice, we have four total electrons

  • which would be the case in a neutral beryllium atom.

  • But what about boron?

  • Boron gets interesting.

  • A neutral boron would have five electrons.

  • So the first two we're going to fill the first shell, 1s2,

  • now the second two are then going to go

  • to the second shell and fill up the s subshell 2s2,

  • and then we're going to start filling up the p subshell.

  • So let's see, we have one more electron so we go 2p1.

  • So we're going to have one electron

  • in one of these p orbitals.

  • And then what happens when we go to carbon?

  • Well it's going to look a lot like boron

  • but now we have one more electron to deal with

  • if we have a neutral carbon atom,

  • it's going to have six electrons.

  • So then an extra electron is once again

  • going to fall into the p subshell

  • in the second shell because that can fit six electrons.

  • So we're going to fill the first shell with two electrons

  • then the 2s subshell with two electrons,

  • and then we have two more electrons

  • for the 2p subshell.

  • Now you can imagine as we get to larger and larger atoms

  • with more and more electrons,

  • this can get quite complex.

  • So one notation folks often use

  • is noble gas configuration

  • where instead of saying, okay, this is carbon,

  • they could say that, hey look,

  • carbon is going to have the electron configuration

  • of helium, remember, the noble gasses

  • are these Group 8 elements right over here,

  • so it's going to have the electron configuration of helium

  • which tells us this right over here,

  • and then from that, we're going to also have 2s2,

  • 2s2, and then 2p2.

  • You could just take helium's electron configuration

  • right over here and put it right over here

  • and you would get exactly what we wrote before.

- [Instructor] In a previous video,

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B2 中上級

電子配置入門|AP化学|カーンアカデミー (Introduction to electron configurations | AP Chemistry | Khan Academy)

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    林宜悉 に公開 2021 年 01 月 14 日
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