Why does bromine exist as Br2 molecules?

Bromine exists as diatomic molecules (${\text{Br}}_2$) because of the electronic structure of halogen atoms. Each bromine atom possesses seven valence electrons in its outermost shell, leaving it one electron short of the exceptionally stable electron configuration characteristic of noble gases.3

To achieve this stability, two bromine atoms share a pair of electrons through a covalent bond. According to molecular-orbital theory, this bond formation is energetically favored because the electrons occupy a bonding molecular orbital at a lower energy level than they would in their separate atomic orbitals. Consequently, like other halogens, bromine naturally occurs as diatomic molecules in all aggregation states.123