BCH1100 Chemistry
Semester B, 2018/19
Tutorial 2
Week 5
Molecular Geometry and Bonding Theories
C. K. Andy Siu
1
Valence‐bond Theory:
Multiple Bonds
Example:
Ethyne (or Acetylene)
One  bond plus two  bonds
• Single bonds are always σ bonds.
• In a multiple bond, there is one σ bond
and all the others are usually π bonds.
2
Valence‐bond Theory: Multiple Bonds
Example: Cumulene
Also see:
MasteringChemistry: Tutorial 2 (Week 5)
3
Resonance Structure, Delocalization and  Bonding
• Resonance structures can be more fundamentally viewed with
the valence‐bond theory.
• A benzene molecule
has six C–C  bonds
and one unhybridized p
orbital on each C atom.
• The  electrons in
benzene are not
localized, they are
delocalized.
• The even distribution of
the electrons in
benzene makes the
molecule unusually
stable.
4
5
6
1. (a) Draw the best Lewis structure(s) for nitrate anion (NO3−).
(b) Determine the formal charge of each atom in NO3−.
(c) Determine the hybridization scheme of the central atom of NO3− .
Answers will be uploaded in Week 7.
7
2. (a) Determine the hybridization scheme of each central atom in the
following molecule (glycine).
(b) How many σ and π bonds in this molecule?
Answers will be uploaded in Week 7.
8
3. How many σ and π bonds in the following molecule (phenylalanine)?
O
NH2
CH
C
OH
CH2
Answers will be uploaded in Week 7.
9