Bromide is a better nucleophile than chloride due to its size and the fact it is a weaker base. In terms of the leaving group, bromide is also the better atom because it is a weak base. Organic chemistry students can use a pKa table to determine the best nucleophile and leaving group.
Both bromide and chloride are commonly found in leaving groups. Leaving groups are the atoms or molecules left over when a chemical bond breaks during a chemical reaction. Bromide is a slightly weaker base than chloride, making it more stable during a chemical reaction.
Nucleophiles are the atoms that donate an electron pair when a bond forms.
There are four main types of nucleophiles.