Question

Which of these molecules has the same number of shared electron pairs as unshared electron pairs? (a) hcl, (b) h2s, (c) pf3, (d) ccl2f2 (e) br2?

Answer 1

H2S has 2 bonds which means that it has two shared electron pairs. It has 2 lone pairs on electrons. It's the only one where the 2 are the same.

Answer 2

Let us check each molecule

a) HCl : the number of shared electron pairs is "one"

the number of unshared electron pairs is six [on chlorine]

b) H₂S : the number of shared electron pairs is "two" as there are two bonds of sulphur with two hydrogen atoms.

The number of valence electrons on sulphur are six, out of these two are involved in bonding and rest four are in the form of two unshared (lone pair) pair of electrons

So in H₂S it has the same number of shared electron pairs as unshared electron pairs

c) PF₃ : the shared pair of electrons are "three"

the number of unshared electron pairs is one on phosphorous.

d) CCl₂F₂ : there are total four shared pair of electrons on carbon and zero unshared electron pairs

e) Br₂ : only one shared electron pair and three unshared electron pairs