00:03
Hi there.
00:04
In this question, we are trying to determine a set of four quantum numbers that best describes the last electron that goes into a magnesium atom.
00:15
So let's talk about quantum numbers briefly first.
00:19
The first quantum number is n, and that is the principal quantum number, and that tells you the energy level.
00:30
The next quantum number is the angular momentum quantum number l, and l ranges from zero to n minus it needs to be an integer.
00:43
So now there was a whole number between zero and n minus one, inclusive.
00:48
So adding to that thought, when l is zero, we have an s -sub shell.
00:55
When l equals one, it's a p sub -shell.
00:59
When l equals two, it's a d.
01:01
And when l equals three, it's an f -subshell.
01:06
Okay, next we have the magnetic quantum number, m -sub -l.
01:10
That refers to which of the orbital shapes we have in terms of their orientation in space.
01:18
So m sub l is again going to be an integer, and it ranges from negative l to positive l.
01:29
So if l is 3, m sub l could be negative 3, negative 2, negative 1, 0, 1, 2, or 3.
01:37
And then we have m sub s.
01:38
M sub s describes the electron.
01:41
That is the spin of the electron.
01:42
The spin can be positive one -half or negative one -half.
01:50
And typically, this is just the convention.
01:53
I mean, the important thing is that if there are two electrons in the same orbital, they have opposite spins.
01:58
But the convention is to typically give the first electron that goes in the positive one -half and the second electron, the negative one -half.
02:07
Okay, so this brings us to magnesium.
02:10
Magnesium is atomic number 12.
02:12
So when we write its electron configuration, we can put neon, the noble gas from period 2 in brackets, that represents the first 10 or the core electrons of magnesium...