CHE 002B: Chemical Bonding II

Molecular Orbital Theory

prediction of properties of molecules

How are molecular orbitals formed?

by adding and subtracting atomic orbitals

• # MO = # AO

Molecular orbitals are linear combination of _____

atomic orbitals

Antibonding

destructive interference; decrease in bonding; higher energy

Bonding

constructive interference; increase in bonding; low energy

Bond Order

#e bonding - #e antibonding/2

Sigma Bond

end-on overlap in larger producing orbitals

Pi Bond

side-on overlap

What bond occur in the p-orbital?

pi bonds

What is the energy order for diatomic O and F?

pi (2p) > sigma (2p)

What is the energy order for diatomic Li and N?

sigma (2p) > pi (2p)

Valence Bond Theory

quantitatively descries how atomic orbitals of dissociated atoms combine to give individual bonds when a molecule forms

The valence-bond method describes ______ as the overlap of _______

1. covalent bonding

2. partially filled orbitals

Hybridization

a mix of orbitals as a result of bonding

HO for linear

sp

HO for trigonal planar

sp²

HO for tetrahedral

sp³

HO for trigonal bipyramidal

sp³d

HO for octahedral

sp³d²

Single bond consist of

1 sigma bond

Double bond consist of

1 sigma + 1 pi bond

Triple bond consist of

1 sigma + 2 pi bond

Every bond contains a ______

sigma bond

Delocalized

when an electron moves around the molecule freely

What does delocalization do for a molecule?

it helps stabilize