Question

$BC{l}_3$ is a planar molecule whereas $NC{l}_3$ is pyramidal because:

• A. Nitrogen atom is smaller than boron atom
• B. $BC{l}_3$ has no lone pair but $NC{l}_3$ has a lone pair of electrons
• C. $B-Cl$ bond is more polar than $N-Cl$ bond
• D. $N-Cl$ bond is more covalent than $B-Cl$ bond

Answer 1

The correct option is B $BC{l}_3$ has no lone pair but $NC{l}_3$ has a lone pair of electrons

$BC{l}_3$ has steric number
$=\frac{1}{2}(3+3)=3$
So it is $s{p}^2$ hybridized and have three bond pairs and zero lone pairs, thus shape being trigonal planar.
Similarly, $NC{l}_3$ has steric number
$=\frac{1}{2}(5+3)=4$
So it is $s{p}^3$ hybridized. It has three bond pairs and one lone pair resulting in tetrahedral geometry and trigonal pyramidal shape.