Question

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

• A. $BC{l}_3$ does not have lone pair on $B$ but $NC{l}_3$ has a lone pair of electrons on $N$
• B. $B-Cl$ bond is more polar than $N-Cl$ bond
• C. $N$ atom is smaller than $B$
• D. $N-Cl$ bond is more covalent than $B-Cl$ bond

Answer 1

Answer: (A)

$BC{l}_3$ does not have lone pair on $B$ but $NC{l}_3$ has a lone pair of electrons on $N$

Boron in $BC{l}_3$ has three valence electrons and they are transferred to three chlorine atoms and it forms $BC{l}_3$, which do not contain lone pairs and have a planar structure.

Nitrogen in $NC{l}_3$ has $5$ valence electrons but only three are shared between $3$ chlorine atoms, but the rest two electrons remain as a lone pair.

Because of this extra lone pair of electrons, $NC{l}_3$ has a pyramidal shape.

Hence, option A is correct.