Structural Theory

1
Structural Theory Structure Determines
Properties

• Structure how atoms are bonded together in a
  molecule
• Bonding Theories from simplest to most complex
• Lewis Theory
• Valence Bond Theory
• Orbital Hybridization
• Resonance
• Molecular Orbital Theory

2
Lewis Theory of Bonding

• Only the valence electrons are involved in
  bonding represent these with dots
• Atoms participate in bonding so as to achieve a
  noble gas electron configuration (a complete
  valence shell)
• Octet for 2nd period and below, duet for hydrogen
• B and Al often settle for six
• Period 3 and lower can exceed octet
• Covalent Bond shared electron pair

3
Figure 1.2 A periodic table of the common
elements seen in organic chemistry
4
So lets write some Lewis Structures CCl4 NH3 H
2O CO2 CH3Br CH4O CO2 PI3 N2H4 H2CO3 C3H8
C3H6
5
Figure 1.3 Summary The usual number of bonds of
common neutral atoms
6
Formal Charge

• Formal Charge can be assigned to each atom in a
  Lewis structure. It is the charge the atom would
  have if its bonding electrons were being shared
  even steven.
• FC the of e-s needed to balance nuclear
  charge minus the of e-s owned by the atom
• FC group - nonbonding e-s ½ bonding e-s