How many electrons are there in ##Br^-##?

The ##"Br"^(-)"## ion has 36 electrons.

The for bromine is 35, which means it has 35 protons in its atomic nuclei. A neutral bromine atom would also have 35 electrons. In order for a bromine atom to become a ##1-## bromide ion, it would have to gain an additional electron.

Below is the Lewis dot structure for a neutral bromine atom, which has seven valence electrons. Below is the Lewis dot structure for a ##"Br"^(-)"## ion, which has eight valence electrons. The extra valence electron gives it a negative charge.

The diagram below shows how a bromine atom gains an electron from the element lithium in order to form the ionic compound LiBr.