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Question

Which species has the smaller bond angle, ClO₄^- or ClO₃^-?

Answer 1

When considering the lewis structures of the two ions they both have 4 areas of high electron density and therefore both have a tetrahedral electronic geometry.

According to the VSEPR theory:

-The molecular geometry of ClO₄^- is also tetrahedral because there are 4 bonded O's and no unshared pairs on the central Cl. The bond angles are 109.5^o

-The molecular geometry of ClO₃^- is Trigonal Pyramidal because there are 3 bonded O's and an unshared pair on the central Cl.

-The unshared pair on the central Cl in the ClO₃^- causes a greater repulsion making the bond angles <109.5.