ClO4- and ClO3-

Question

why does ClO₃^- have a smaller bond angle then ClO₄^-

Answer 1

Based on Lewis Dot structure of ClO₃^- , the shape of ClO₃^- is trigonal pyramidal and there are 3 bond pairs and 1 lone pair. This one lone pair of electrons exerts a big repulsive force on adjacent bond pairs to compress bond angles to make them smaller than 109.5^o and it is 107^o.

But ClO₄^- ion is tetrahedral shape and has 4 bond pairs and no lone pair of electrons, and bond angle is 109.5^o.