# Homework Help: Use the periodic table to write the electron configuration of Gd

1. Jun 29, 2007

### skander

1. The problem statement, all variables and given/known data
Use the periodic table to write the electron configuration of Gd.

2. Relevant equations

3. The attempt at a solution

Gd has 64 electrons (atomic number 64) so I would assume that the configuration would be:
1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f8 5s2 5p6 6s2

However when I checked my answer on a site that gave Gd's electron configuration it gave the configuration like this:
1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f7 5s2 5p6 5d1 6s2

Does anyone know why they would write it like that and are they correct or am I?
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Jun 29, 2007

### CaptainZappo

If you look at the periodic table, the 4f8 spot is occupied by Tb. This should immediately raise a flag when reviewing your answer.

Following straight across the periodic table, the orbitals are filled up in the following order:

[Xe] 6s2 5d1 4f7

I hope this helps.

3. Jun 29, 2007

### skander

Okay, since Tb is 4f8 Gd has to be 4f7 giving rise to 5d1. Now when you wrote it as 6s2 5d1 4f7 was that specifically in that order? Because I thought we were supposed to write down electron configuration by 1, 2, 3, 4, 5, 6 regardless of which orbital was actually filled last. Thanks.

4. Jun 29, 2007

### CaptainZappo

Your teacher should specify the way he/she wants it done. My high school teacher wanted it done in the 1, 2, 3, 4, ... way, while my college professor requested that we try to represent the order in which the orbitals are actually filled.

5. Jun 29, 2007

### skander

Okay so I'm supposed to it the 1, 2, 3, ... for my course. Thank you very much for all your help.