(b) Restatement: The OH bond angle of H 3 O+is less than 109.5°.
- Lewis structure of H 3 O+:
•H 3 O+is pyramidal in geometry due to a single pair of unshared electrons.
- Angle of tetrahedron is 109.5°; this exists only if there are no unshared electrons.
- Repulsion between shared pairs of electrons is less than repulsion between an unshared
pair and a shared pair. This stronger repulsion found in the shared-unshared pair condi-
tion, as seen in H 3 O+, decreases the bond angle of the pure tetrahedron (109.5°).
(c) Restatement: Compare CO bond lengths as found in CO and CO 3 2– - Lewis structure of CO:
- Lewis structures of CO 3 2–
- CNO–exists in three “resonance” forms. CO bond length is considered to be the average
of the lengths of all single and double bonds.
(d) Restatement: CNO–ion is linear. - Lewis structure of CNO–:
- There are no unshared pairs of electrons around the central atom N, resulting in a linear
molecule. - The molecule is polar because O is more electronegative than C.
C N O
−
O
O O
C
O
O O
C
O
O O
C
2 − 2 − 2 −
CO
H
H
HO
+
Part IV: AP Chemistry Practice Test