Q. The correct order of F-M-F bond angles (where M is the central atom) in
NSF3, SiF4 and POF3 is:
(A) NSF3 > SiF4
(B) SiF4 > NSF3
(C) NSF3 > POF3
(D) SiF4 > POF3
First of all write the Lewis dot structures for the molecules and find the number and
types of electrons pairs; magnitude of repulsions between them to arrive at the
relative bond angles.
to the VSEPR theory, the repulsion increases with increase in the volume
occupied by electron pair(s). Since the electron density in triple bond
occupies more space, it exerts more repulsion than that of double bond and
which turn exerts more repulsion than that of single bond.
POF3, there is a double bond between Phosphorus and Oxygen atom,
which also causes more repulsion than single bond, but less than the triple
bond. Hence the bond angle will be medium in POCl3.(Bond angle
almost 101o )
bond angle is least affected in case of SiF4, since all the Si-F
bonds are single bonds, which exert less repulsion on other bond pairs. Therefore
the bond angle is same as the tetrahedral molecule i.e. 109o28'
NSF3, there is a triple bond between N and S. Hence the repulsions
will be more on S-F bond pairs. This will reduce the bond angle more than in