Ncert Exercises & Solutions

BCl₃ exists as monomer whereas AlCl₃ is dimerised through halogen bridging. Give reason. Explain the structure of the dimer of AlCl₃ also.

Boron halides do not exist as dimer due to small size of boron atom which makes it unable to accommodate four large sized halid ions. AlCl₃ exists as dimer. Al makes use of vacant 3p-orbital by coordinate bond i.e., Al atoms complete their octet by forming dimers.