00:03
There.
00:04
This question wants us to first explain what valence electrons are.
00:10
And valence electrons are those electrons in an atom in the highest energy level.
00:27
That means for the representative elements, it will be the s &p electrons in that highest shell.
00:57
Okay, so we've defined valence electrons, and then it says that for representative elements, the number of electrons is equal to the group number.
01:06
And it wants us to show that this is true.
01:09
So in other words, we have group 1a, we have group 2a, we have group 3a, 4a, 5a, 6a, 7a.
01:18
So it is saying that the number of valance electrons corresponds to that group.
01:22
So it wants us to show that that is true for several elements here.
01:27
So let's start with aluminum.
01:29
To show this, i'm going to draw its shorthand electron configuration, where we put the noble gas, in brackets, and then we just show the valence shell.
01:41
So 3s2, 3p1.
01:44
If we add all of the third energy electrons together, the 2s electrons and the 1p electron, we get three valence electrons.
01:56
So sure enough, aluminum is in group three and has three valence electrons.
02:01
Let's look next at strontium.
02:06
Strontium is over here in group 2, so its electron configuration.
02:14
He's going to have krypton in brackets, and then 5s2.
02:20
In other words, two valence electrons.
02:24
And sure enough, that corresponds to group 2 where we find strontium.
02:29
Next we have potassium.
02:33
So potassium is over here in group 1a.
02:38
Let's look at its electron configuration to see if it indeed...