## Homework 2.55

alexagreco1A
Posts: 34
Joined: Fri Apr 06, 2018 11:03 am

### Homework 2.55

Give the notation for the valence-shell configuration (including the outermost d-electrons) of (b) Group 15 elements.

Why does the notation, ns^1np^3, not include d if some of the group 15 elements have d in their electron configuration?

Emma Leshan 1B
Posts: 30
Joined: Fri Apr 06, 2018 11:03 am

### Re: Homework 2.55

Group 15 includes N, P, As, Sb, Bi. Each has a valence electron configuration of (n-1)d10 ns2 np3, the d group is not included because the electrons in the d subshell are in the shell n-1, so they aren't valence electrons. For example, arsenic has a configuration of [Ar] 3d10 4s2 4p3. Because the d subshell is in shell n=3, the electrons in the d subshell are not valence electrons.

AnthonyDis1A
Posts: 30
Joined: Fri Apr 06, 2018 11:05 am

### Re: Homework 2.55

For atoms with an atomic number greater than 20, the 4s state is higher in energy than that of 3d, which is why the d subshells are written before the s subshells for those e- configurations. Just looking at the configurations, the 4s and 4p subshells are the two "written last" of the Group 15 elements, and so are the electrons residing at the outermost electron shell.