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.