# How many half-filled orbitals are in a bromine atom?

Aug 13, 2016

In a bromine atom, you have the electron configuration $\left[A r\right] 4 {s}^{2} 3 {d}^{10} 4 {p}^{5}$.

The only half-filled orbitals could be one of the $\boldsymbol{4 p}$ orbitals.

You can convince yourself that since each orbital has a maximum of $2$ electrons, and there are one $4 s$ and five $3 d$ orbitals, both those subshells are doubly-occupied in each orbital, seeing as how there are $2$ electrons in the $4 s$ orbital and $10$ in the $3 d$ orbitals.

(Hence, the $4 s$ and $3 d$ are all full.)

Therefore, we examine the $4 p$ orbitals and fill them one at a time, then double up afterwards, in accordance with Hund's Rule:

$\underline{\uparrow \downarrow} \text{ " ul(uarr darr) " } \underline{\uparrow \textcolor{w h i t e}{\downarrow}}$
$4 {p}_{x} \text{ "" " 4p_y " "" } 4 {p}_{z}$

So now, how many $4 p$ orbitals are half-filled? At this point you should be able to answer your own question. :-)