Question

Which of the following molecules does not show back bonding?

• A. $BC{l}_3$
• B. $N(Si{H}_3{)}_3$
• C. $CaS{O}_4$
• D. $B{F}_3$

Answer 1

The correct option is C

$CaS{O}_4$

Back bonding occurs between the atoms in a compound in which one atom has a lone pair of electron and the other has a vacant orbital placed adjacent to each other.

$BC{l}_3$ shows back bonding when the lone pair on chlorine atom is donated to the vacant $2p$ orbital of boron.

In $N(Si{H}_3{)}_3$, the nitrogen atom has a lone pair of electrons and silicon has vacant 3d orbitals. Hence, back bonding occurs between the lone pair of $N$ and the empty d- orbital of $Si$.

$CaS{O}_4$ is an ionic molecule with an ionic bond between $C{a}^{2+}$ and $S{O}_4^{2-}$ ion. In the sulphate ion, $S$ and $O$ atoms are bonded by covalent bonds. Back bonding is only valid for covalent compounds.

$B{F}_3$ shows back bonding when a lone pair on $F$ atom is donated to the vacant $2p$ orbital of boron.