Question

Which of the following compounds does not have a trigonal planar geometry?

• A. $B{H}_3$
• B. $C{O}_3^{2-}$
• C. $S{O}_3^{2-}$
• D. $N{O}_3{}^{-}$

Answer 1

The correct option is C $S{O}_3^{2-}$

As you can see in the image $S{O}_3^{2-}$ is form trigonal pyramidal. The VSEPR Theory states that the electron sets attached to the central atom want to be as far away as possible from each other. So since each oxygen atom needs 8 electrons to be satisfied, they equally share with the Sulphur atom. So since the oxygen have a (-) charge and the sulphur has a (+) charge, the single oxygen and Sulphur cancel out, and form a double bond, leaving the other two Oxygen to stay negative and have two extra valence electrons. Now, applying VSEPR, the oxygens stay as equally far as they can from each other. Since there are 3 bonding pairs, the structure is trigonal pyramidal, with 109.5 bond angles.