Cliffs AP Chemistry, 3rd Edition

(b) Restatement: The OH 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 CO 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