barium chloride exist as a monomer even though electron deficient, where as aluminium chloride as dimer.give reason.

Hi Tsubin66,

There seems to be some ambiguity with your question. It must be baron instead of barium.

 

Well, then in that case the answer is as follows.

In AlCl₃, aluminium has got 6 electrons in its valence shell. To complete its octet, it requires 2 more electrons. It accepts a lone pair of electrons from Cl of the neighbouring AlCl₃ molecule. In doing this, one of the chlorine atoms donates an electron pair to the electron pair to the electron deficient Al atom of the neighbouring AlCl₃ molecule resulting in the formation of a dimer.

On the other hand, due to small size of boron, it cannot accommodate four large sized chlorine atoms around it and thus, it exists as a monomer.

Hope, this answers your question.

Best wishes!