Draw the structures of and (dimer)
is the covalent compound which has 6 electrons in the valence shell. Thus it is an electron acceptor and needs 2 electrons to become an octet. It is a Lewis acid and can react with as it donates electrons easily and is a Lewis Base. They combine as shown
In , Al has 6 electrons in the valance shell and functions similarly as B and thus combines with Chlorine to form an octet.