In this video i'm gonna give You a Simple Introduction on how to write the Electron Configuration of an Element so
Let's talk about Nitrogen so how can we write the Electron Configuration for an atom of Nitrogen
So That's how Nitrogen Looks like on a Periodic table?
So the higher these two numbers is the mass Number and the smaller of the two numbers is the atomic Number Which Is an integer
Now we Need to know is that in the first energy Level you have the one s sublevel in
The Second Energy Level You have the S and the P Sublevels. In the Third Energy Level You have s p and D.
Now for Nitrogen This is as far as we need to go
The S sublevel can hold Two electrons and the P subevel can hold 6 and can hold 10
Now you want to write the Electron Configuration
Until You get a total of seven. Now for an atom of Nitrogen
It contains seven protons and seven Electrons but we're focused on the number of Electrons
Because we're writing The Electron Configuration for Ions That number could differ but for atoms
you just need to focus on that number so the number of Electrons in this problem is seven
So here's what we need to do. First start with 1s
So i'm going to write 1s2 because S can hold up to 2 electrons
Next move on to the 2S sublevel.
2S can also hold 2 electrons
and then after 2S you want to go to 2P and then 3S.
Now  2P can go up to six it can hold six electrons but we only need three more
Because if you add the exponents, 2 + 2 + 3 = 7.  So once you get up to this number for atoms
you can stop. This is the Electron Configuration for an atom of Nitrogen
Now Let's try another example.  Let's write The Electron Configuration for Aluminum. You could try if you want you
So we're dealing with an atom of Aluminum which Has 13 electrons. So you want to write the configuration up to 13
Now we're gonna set It up the same way.
Now if you want to you can add the fourth Energy Level which contains 4S 4P 4D and 4F
Now let's put these numbers again.  F can hold Up To 14 electrons
So we're gonna start with 1s
so that's 1s2 and
Then after 1S we have the 2s sublevel so this is gonna be 2s2 and
Then we need to move on to 2p then 3s
So P can hold up to 6 and
S can hold up to 2 so if we add the numbers 2 + 2 + 6 + 2
That's 12 we only need one more
So after 3S we need to move on to 3P
Now we don't need to go up to 3P6.  We only need one more so we're gonna stop at 3P1.
so if you add 2 + 2 + 6 + 2 + 1
That will give you a total of 13.
So this is the ground state
Electron Configuration of an atom of aluminum
Now what about ions?
Let's say If we want to write the Electron Configuration of the Fe 2+
How can we do so?
Now on a periodic table
Fe has an Atomic Number of 26 and an average Atomic Mass of about 55.85
So an atom of Iron metal has 26 electrons so what about an ion of Fe?
Because the charge is plus 2 that means that the atom lost two electrons so
Therefore the Fe 2+ Ion has 24 Electrons. It has 2 less than this number.
So we're gonna write the Electron Configuration
Based on the Number 24
So let's make our list Again 1S 2S 2P 3S 3P 3D
4S 4P 4D 4F.
S can hold 2, P can Hold 6, D can hold 10, F can hold 14
So we're gonna start With 1s
so that's gonna be 1s2
and then we're gonna move on to 2S so this is gonna be 2s2 and
Then we're gonna go to 2p then 3s
So it's gonna be 2p6 and
Then 3s2
Now after 3s we got to move on to 3p then 4s
so it's 3p6
and then 4s2
By the way, before you write the Electron Configuration of Fe 2+
It's better if you write the Electron off
Excuse me if you write the Electron Configuration of the parent atom and then from that
Write the Electron Configuration of the ion. so i'm gonna focus on 26 and then I'm going to adjust it to 24
So right now, we have a total of 2 plus 2 plus 6 = 10
2 plus 6 plus 2 is another 10 so we need 6 more Electrons to get to
26
So after 4s comes The 3d Sublevel.  Now d can hold up to 10 but we only need 6 more
So this is the Electron Configuration of Fe but not Fe 2+
Because we have a total of 26 electrons
Now from this expression You want to write the Electron Configuration of Fe 2+
So you need to remove two electrons.
The question is which two electrons do you remove?
Now what we need to do is to remove Electrons from the highest
Energy level so that's from the fourth energy level so you're gonna take off these two electrons
So we could therefore write the configuration for Fe  2+ as 1s2 2s2
2p6 3s2 3p6 4s2
or you could just omit It and then 3d6
Now if you were to write the configuration based on this number and if you didn't do this step first
You might be Inclined to write 4s2 3d4 and It won't be correct so when you're dealing with
Transition metal ions, it's best to write the configuration of the parent atom first and then if you have a positive charge
Simply take off Electrons that's equal to the charge
starting from the highest energy level.
Now let's move on to our next example.
So we're gonna deal with chlorine
So here's the information that you need to know for chlorine. Now what i want you to do is write the Electron Configuration
for the Chloride Ion.
Go ahead and try that problem
Now for Chlorine, we really don't need the fourth energy Level.
So let's start with this.  We need to get up to 17 and then we're gonna add one.
Chloride has a total of 18 Electrons.
Now for this one we
can just go straight to 18. We don't have to start from 17 and add them.  You could do that If you want
To but you don't have to.
Because Chlorine is not a transition metal.
So i Just want to rephrase this one more time.  For transition metals, it's best to write the Electron Configuration first and
then subtract the appropriate number of electrons based on the charge.
For elements that are not transition metals and If you're dealing with ions,
you can go straight to this number.
You could find the total number of Electrons in the ion and then write the configuration based on that.  You don't
have to write the configuration of The atom and then adjust it for the
for the Ions.   It just simply works out that way.
But
You could do It both ways for these elements.
So if you decide to write the Electron Configuration for the parent atom and then adjust It for the ions, then that's fine.
For negatively charged Ions, you need to add electrons.  For positively charged ions, you need to subtract the electrons.
So let's start.   We need to get up to 18.  So we're gonna start with 1s.  So this is gonna be 1s2.
and then it's gonna be 2s2
After 2s comes 2p then 3s
so it's 2p6 and then 3s2
So far we have a total of
12 so we need six more and
3p
can hold up to 6, so we're gonna stop at 3p6.
This is the Electron Configuration for the chloride ion. For Chlorine,
It's everything Up to 3p5 but for chloride it's 3p6 you gotta add one to it.
