Question

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

Answer 1

In a bromine atom, you have the electron configuration `[Ar] 4s^2 3d^10 4p^5`.

The only half-filled orbitals could be one of the `bb(4p)` orbitals.

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

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

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

`ul(uarr darr) " " ul(uarr darr) " " ul(uarr color(white)(darr))`
`4p_x " "" " 4p_y " "" " 4p_z`

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