Chemistry: The Molecular Science (5th Edition)

$1s^22s^22p^63s^23p^63d^{10}4s^24p^6$
We write the electron configurations, using the information that we learned over the course of the chapter. The Bromide ion has one more electron than neutral Bromine. Recall, we start at 1s and move up: $1s^22s^22p^63s^23p^63d^{10}4s^24p^6$