Chapter 9: Advance Theories of Covalent Bonding

electrons overlap to form a pair of electrons

a bond

the same amount of energy required to make abond is the same amount of

energy to break a bond

bond energy (enthalpy) is proportional

to bond length ( the shorter the bond, the stronger the bond)

single bonds are known as

sigma bonds in VB (valence bond theory)

Sigma in VB could be

1. overlap of two “s” electrons"

2. overlap of an “s” and a “p”

   1. overlap of end to end of 2p orbital electrons

single bonds are

where the electron density is along the internuclear plane (x-axis)

when you have two sets of “p” electrons overlapping you have one in the internuclear plane and one above and below

This side-by-side above/below is called a pi bond

a double bond conists of one

sigma and pie bond

a triple bond consist of one

signma and two pi bonds

Mix “S” and other “s” electrons

1s orbital linear

“s” and a “p”

2 sp orbitals = linear

“s” and two “p” electrons

3sp2 tigronal planar

“s” and three “p” electrons

4sp3 orbitals tetrahedral

“s” and three “p” and “d”

5sp3d tigonal bipyramidal

“s” and three “p” and two “d”

6sp3d2 octahedral

molecular orbital theory

regions of space predicting where electrons should be

paramagnetic

diamagnetic

homonuclear

heternuclear

when electrons combine in inphase they yeild

lower energy(bonding) sigma or pi electron sets

when combining out of phase they yield

higher energy (anti-bonding) pi or sigma sets

stability = more bonding e- than anti-bonding;

=more stable = more likely to exist

bond order (BO)

(#bonding electrons - anti-bonding electrons/ 2

If BO = zero,

no bond between the atoms, molecule does not exist

If BO = 0,

single bond

IF BO=2,

double bond

If BO=3

triple bond; if fractions then “average” bonds and resonance

different templates for

different molecules

resoannce structures show stability in a moleucle/ion because

the overllaping pi electrons are delocalized, lower energy.