L1 /
7
CH1012
LCAO APPROXIMATION
Linear Combination of Atomic Orbitals
• Electrons are not localised on an atom they
are delocalised in MOs which are linear combinations
of AOs eg. s1s = 1s + 1s
• The electrons
belong to the molecule as a
whole (not to the atoms).
whole (not to the atoms).
• The combination of 2 AOs ® 2 MOs
bonding + antibonding
bonding + antibonding
• The bonding MO
is always lower in E than
the antibonding MO and the starting AOs.
the antibonding MO and the starting AOs.
• Electrons fill the lowest
MOs first (aufbau)
• Only 2 e- are allowed in a MO
(Pauli)
