F.5Chemistry-microscopic world

(a)
BeCl2 and AlCl3­ are covalent compounds.


(b)
Both BeCl3­ and AlCl­3­ are non-polar.

Be-Cl bond is polar. However, BeCl2 is a symmetry molecule which is linear in shape. The dipole moments of the two Be-Cl bonds cancel each other, and thus the net dipole moment of BeCl2­ molecule is 0. Therefore, BeCl2 molecule is polar.

Al-Cl bond is also polar. However, AlCl3 is a symmetry molecule which is triangular planar in shape. The dipole moments of the three Al-Cl bonds cancel each other, and thus the net dipole moment of AlCl3 molecule is also 0. Therefore, AlCl3­ molecule is non-polar.