# The atom having the valence-shell configuration 4s^2 4p^5 would be in what group and period?

Jan 4, 2017

The atom would be in Period 4 and Group 17.

#### Explanation:

The valence shell configuration is ${\text{4s"^2 "4p}}^{5}$.

The principal quantum number (4) gives you the Period number.

Start with H in Period 1 and count down to the fourth row (Period 4).

That brings you to $\text{K}$.

Now, start counting to the right through the $\text{s}$-block to $\text{Ca}$ (${\text{4s}}^{2}$) and the $\text{d}$-block to $\text{Zn}$.

Now that you have come to the $\text{p}$-block, count five more atoms, for a ${\text{4p}}^{5}$ configuration.

This brings you to the desired atom, $\text{Br}$.

You have counted horizontally through 17 atoms, so $\text{Br}$ is in Group 17.