Placeholder Image

字幕表 動画を再生する

  • - [Instructor] We are told that the first five

  • ionization energies for a third period element

  • are shown below.

  • What is the identity of the element?

  • So pause this video

  • and see if you can figure it out on your own

  • and it'll probably be handy

  • to have a periodic table of elements.

  • So before I even look at a periodic table of elements,

  • let's make sure we understand what this table

  • is telling us.

  • This is telling us that if we start with a neutral atom

  • of this mystery element,

  • it would take 578 kilojoules per mole

  • to remove that first electron

  • to turn that atom into an ion

  • with a plus one positive charge.

  • And then, it would take another 1,817 kilojoules per mole

  • to remove a second electron.

  • So to make that ion even more positive.

  • And then after that it would take another

  • 2,745 kilajoules per mole to remove the third electron.

  • And then to remove the fourth electron,

  • it takes a way larger amount of energy.

  • It takes 11,578 kilojoules per mole.

  • And then the fifth electron takes even more,

  • 14,842 kilojoules per mole.

  • And so, for the first, second, and third

  • you do have an increase in ionization energy,

  • but when you go to the fourth the energy required

  • to remove those is way higher.

  • So to me, these look like you're removing valence electrons

  • and these look like you're removing core electrons.

  • So one way to think about it is

  • let's look on our periodic table of elements

  • and look for a third period element

  • that has three valence electrons.

  • So we have our periodic table of elements.

  • We want a third period element,

  • so it's gonna be in this third row

  • and which of these has three valence electrons?

  • Well, sodium has one valence electron,

  • magnesium has two valence electrons,

  • aluminum has three valence electrons.

  • So one way to think about it is

  • that first electron, it's a reasonable ionization energy.

  • Then the second one, a little higher.

  • Then the third, a little bit higher than after that,

  • but then the fourth, you're starting to go into the core.

  • You're going to have to take an electron

  • out of that full second energy shell,

  • which takes a lot of energy.

  • And so this is pretty clearly aluminum

  • that is being described.

- [Instructor] We are told that the first five

字幕と単語

ワンタップで英和辞典検索 単語をクリックすると、意味が表示されます

B2 中上級

実践例。連続する電離エネルギーから元素を同定する|カーンアカデミー (Worked example: Identifying an element from successive ionization energies | Khan Academy)

  • 2 0
    林宜悉 に公開 2021 年 01 月 14 日
動画の中の単語