Typically just one to acieve the noble gas configuration of krypton.
However as bromine is in period 4 its outermost shell is the fourth energy level so it is able to accept more electrons and can form compounds such as BrF5
Bromine's atomic number is 35, so it has 7 valence electrons. To achieve 8 valence electrons and a full outer shell, bromine needs to gain one electron.
It'll have to gain one to have a stable octet.
Neutral Bromine has three complete rings of electrons. The first ring consists of 2 electrons, the second has 8, the third 18, and the fourth has a maximum capacity of 8 electrons. Bromine only has 7 electrons in it's outer ring, though, so it needs one extra electron to complete it's ring. So to answer your question, it needs ONE more valence electron.
4
Bromine (Br) tends to gain electrons. As a halogen, it has seven valence electrons and seeks to achieve a full octet by gaining one additional electron. This makes bromine more likely to form negative ions (anions) in chemical reactions.
it only needs 1 more valence electron. it has seven and wants eight like all ofthe other elements.
They will gain 3 electrons from something with 3 valence electrons.
it is in the oxygen family and has 6 valence electrons it requires 2 electrons
Phosphorus, with 5 valence electrons, needs to gain 3 electrons to have a full set of 8 valence electrons. This would allow it to achieve a stable octet configuration, resembling the noble gas configuration of argon.
Nitrogen has five valence electrons as a neutral atom, but it is shooting for eight. So it needs to gain three more electrons.
the electrons on their outer shell, all atoms want to gain a full valence shell.
An atom with 4 valence electrons will have to either gain 4 electrons or lose 4 electrons to achieve a full set of eight electrons.