Question

Select the correct statement(s) for following molecules:
(I) $P{F}_2(C{H}_3{)}_3$
(II) $P{F}_2(C{F}_3{)}_3$

• A. both have trigonal bipyramidal structure.
• B. both have the same dipole moment.
• C. $P-F$ bond length is longer in $P{F}_2(C{H}_3{)}_3$ than in $P{F}_2(C{F}_3{)}_3$
• D. $P-F$ bond length is longer in $P{F}_2(C{F}_3{)}_3$ than in $P{F}_2(C{H}_3{)}_3$

Answer 1

Answer: (A), (B), (C)

The correct options are
A both have trigonal bipyramidal structure.
B both have the same dipole moment.
C $P-F$ bond length is longer in $P{F}_2(C{H}_3{)}_3$ than in $P{F}_2(C{F}_3{)}_3$

In both the molcules, $5$ bond pairs and zero lone pairs are present. The central $P$ atom in both the molecules undergoes $s{p}^{3}d$ hybridization. Hence, shape is trigonal bipyramidal for both the molecules.
(b) The net dipol moment ${\mu }_D$ of both the molecules I and II is equal to zero as all substituents are symmetrically arranged due to which the individual bond dipoles cancel each other.
(c) According to Bent's rule, $P-F$ bond length in $P{F}_{2}M{e}_3$ is longer than $P{F}_2(C{F}_3{)}_3$, because as a whole group $C{F}_3$ is electronegative than $C{H}_3$ group by which polarity of $P-F$ bond increases in $P{F}_2(C{F}_3{)}_3$ and $P-F$ bond length decreases.
Hence, the statements A,B and C are correct and the statement D is incorrect.