Question

A molecule has 3 bond pairs and 1 lone pair on the central atom. Identify the molecule.
(a)- $Cl{{F}_{3}}$
(b)- $S{{F}_{6}}$
(c)- $C{{H}_{4}}$
(d)- $PC{{l}_{3}}$

Answer 1

Bond pairs are those pairs of an electron which helps two atoms to remain with each other and lone pairs are the extra unbonded electrons on the atom. Find the central atom, then count the number of valence electrons of the central and then count the number of atoms joined to the central atom. The remaining number of valence electrons will be the lone pairs of the atom.

Complete step by step solution:
Bond pairs are those pairs of an electron which helps two atoms to remain with each other and lone pairs are the extra unbonded electrons on the atom. We are given the compound has 3 bond pairs and 1 lone pair.
Find the central atom, then count the number of valence electrons of the central and then count the number of atoms joined to the central atom. The remaining number of valence electrons will be the lone pairs of the atom.
Let us study all the options one by one:
(a)- $Cl{{F}_{3}}$: In this compound, the central atom is chlorine and the number of valence electrons is 7. There are three fluorine atoms present, so there will be 3 bond pairs and 4 electrons, i.e., 2 lone pairs.
(b)- $S{{F}_{6}}$: In this compound, the central atom is sulfur and the number of valence electrons is 6. There are six fluorine atoms present, so there will be 6 bond pairs and 0 lone pairs.
(c)- $C{{H}_{4}}$: In this compound, the central atom is carbon and the number of valence electrons is 4. There are four hydrogen atoms present, so there will be 4 bond pairs and 0 lone pairs.
(d)- $PC{{l}_{3}}$: In this compound, the central atom is phosphorus and the number of valence electrons is 5. There are three chlorine atoms present, so there will be 3 bond pairs and 2 electrons, i.e., 1 lone pair.

Therefore, the correct answer is an option (d).

Note: If the atom is univalent, then only one electron of the central atom will form the bond-like hydrogen and halogens, but the atom is divalent like oxygen, then it will form a double bond and two electrons will be involved.