Boron with atomic number 5 belongs to Group-IIIA in periodic table. The electronic configuration of Boron is,
1s², 2s², 2p¹
As there are 3 electrons in valence shell of Boron so it can make three covalent bonds.
Bromine with atomic number 35 belongs to Group-VIIA in periodic table. The electronic configuration of Bromine is,
1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹⁰, 4p⁵
As there are 7 electrons in valence shell of Bromine so it can make single covalent bond to complete its octet.
Compound of Boron and Bromine:
One atom of Boron with capacity of forming three covalent bonds combines with three Bromine atoms with capacity of forming single bond to form Boron Tribromide (BBr₃).
