Question

In which of the following molecules the central atom does not retain any lone pair of electrons?
A. ${{N}}{{{O}}_2}$
B. ${{N}}{{{H}}_3}$
C. ${{B}}{{{F}}_3}$
D. ${{{H}}_2}{{O}}$

Answer 1

Lone pair of electrons is also termed as non-bonding pair of electrons. Those pairs of electrons which do not take part in the bonding of atoms are referred to as lone pairs of electrons or non-bonding pairs of electrons.

Complete step by step answer:
When a covalent bond is formed between atoms in a molecule, the central atom will have a bonding pair of electrons and a nonbonding pair of electrons. Covalent bond is formed by the bonding pair of electrons which are present in the outermost shell of the atom. These electrons can also take part in coordination bonds.
Now let’s move on the options.
A. Nitrogen has the electronic configuration $\left[ {{{He}}} \right]{{2}}{{{s}}^2}{{2}}{{{p}}^3}$. Nitrogen has three hybridized orbitals in which there are two $\sigma$ bonds and a lone pair of electrons. Thus it forms ${{s}}{{{p}}^2}$ hybridization.
B. In this molecule, nitrogen has three $\sigma$ bonds and a lone pair of electrons. It has a pyramidal geometry.
C. In ${{B}}{{{F}}_3}$ molecule, the electronic configuration of boron is $\left[ {{{He}}} \right]{{2}}{{{s}}^2}{{2}}{{{p}}^1}$. It forms three bonds with fluorine atoms. Thus no more electrons are left in it. Thus it has no lone pair of electrons. It has trigonal geometry.
D. In ${{{H}}_2}{{O}}$, there are only two bonded groups. It also has two lone pairs of electrons. It has a bent shape.
Thus we can say that only ${{B}}{{{F}}_3}$ has no lone pair of electrons.

So, the correct option is C.

Note: When there is a large difference between the electronegativity of two atoms, then there forms the lone pair of electrons. Also, when there is a difference in the electronegativity between the central atom and the bonded atom, a lone pair is formed in the hybrid orbital.