Question

Aluminium(III) chloride forms a dimer because aluminium:

• A. Belongs to $3^{rd}$ group
• B. Can have higher coordination number
• C. Cannot form a trimer
• D. Has high ionization energy

Answer 1

The correct option is B Can have higher coordination number

$AlC{l}_3$ forms a dimer, as $Al$ due to the presence of $3d-$orbitals can expand its covalency from four to six. Also dimerisation enables Al atoms to complete their octets.