## 2.55 - what does valence-shell configuration mean?

Anna De Schutter - 1A
Posts: 66
Joined: Wed Feb 21, 2018 3:01 am

### 2.55 - what does valence-shell configuration mean?

Hi!

Problem 2.55 says: "Give the notation for the valence-shell configuration (including the outermost d-electrons)". I'm a bit confused, what does valence-shell configuration mean? For example, for part b it asks us to give the valence-shell configuration of group 15 elements and I was just going to answer np^3 because I thought that was the outermost shell (the correct answer for the group 15 elements is ns^2 np^3, why do we add ns^2?). Can someone explain this to me?

Thank you so much!
Anna De Schutter - section 1A

Bianca Nguyen 1B
Posts: 36
Joined: Fri Apr 06, 2018 11:04 am

### Re: 2.55 - what does valence-shell configuration mean?

A shell basically represents a principle quantum number. You can think of it as n=shell, l=subshell, and ml=orbitals of a subshell. For every period in the periodic table, the s and p block will always be in the same shell or have the same principle quantum number (for ex., 2s and 2p, 3s and 3p). So if you write down the p block for the valence-shell configuration, you must write down the s as well since they are in the same shell.

Anna De Schutter - 1A
Posts: 66
Joined: Wed Feb 21, 2018 3:01 am

Thank you!! :)