EN

ER

GY

H H

Far apart no attraction

H H

H H

H HAttractionMost Stable

Repulsion

Potential Energy of the Hydrogen Molecular as a Function of Internuclear Distance

104 kcal mol-1

Internuclear Distance

Bond Length of the H-H bond

Pictorial Representation of Bonding and Antibonding Orbitals for the Hydrogen Molecule

addition of orbitals with opposite phases

addition of orbitals with the same phase

Bonding Orbital

Anti-bonding Orbital

-+ +

-

+

-

Planar Wave Has Positive and Negative Phases

Electron has wave characteristics and this includes positive and negative phases

Do not confuse the phase with the charge of the electron!

Wave Characteristics of the Electron

+ +Overlaping Waves of the same phase reinforce

+-

Overlaping Waves of opposite phase produce a node (zero applitude)

node

Energy Diagram For the Hydrogen Molecule

Bonding Molecular Orbital

Antibonding Molecular Orbital

EN

ER

GY Atomic

OrbitalAtomic Orbital

Energy of the isolated hydrogen atom

Energy of the isolated hydrogen atom

Mixing of Atomic Orbitals to Make Hybrid Orbitals

Mix 1 2s with 3 2p orbitals

get

4 sp3 orbitals

25% s character 75% p character

Overlap of a sp3 hybrid orbital with a 1s orbital to make a

sigma C-H bond.

Methane has 4 C-H sigma bonds.Four bonds of equal length. Bond vector separated by 109.5°. This angle also happens to be the angle that places the substituents around the carbon as far apart as possible. Since each electron pair of the 4 sigma bonds will be concentrated between the C-H atoms, the bond angle minimizes the repulsion between the electron pair of one bond and its 3 neighbouring bonds

C

H

H

H

H

H

C

HH

H

109.5º

bond anglebond length

Structure of Ethane

C2H6

Lewis or Dot Structure Line Bond Structure 

C

H

H

H

C

H

H

H

H C C H

H

H

H

H

H

C C

H

H H

HH

Sigma bond caused by

overlap of two sp3 orbitals

C C

C C

H

H

H

H

C C

H

H

H

H

Trivalent carbonnot allowed

C

H

H

CH

H

Line Bond Structure Lewis Structure

Tetravalent carbon

Hybridization: The structure of Ethene or Ethylene - sp2 Hybrid Orbitals Ethylene C2H4

 Since Carbon is tetravalent ethylene must contain a carbon to carbon double bond.

C

Viewed from above

120º

120º

120º

Viewed from sideunhybridized p orbital

C

sp2 hybrid orbitals

sp2 Hybridization

H

H

H

H

Ethylene C2H4

C C

Overlap of 2 sp2 orbitalsgives C-C sigma bond

H

H

H

H

C C

H

C C

H

H H

HH C C

Overlap of 2 sp orbitalsgives C-C sigma bond

H C C H HH C C

Acetylene C2H2sp Hybridization:-

Predicting Shapes of Molecules Valence-Shell Electron Pair Repulsion VSEPR

Model - electrons in a molecule arrange themselves to minimize electrostatic repulsion. CCl4 like methane (CH4) is tetrahedral because this

is how the four groups of electron pairs that make the bonds between carbon and chlorine can be the farthest apart.

To Apply this idea use the following steps:-

1. Count electron groups on an atom. These are of the following type

Lone Pair - one groupAny pair or set of pairs of electrons - one group.

2. Assume each group moves as far apart as possible.

Valence-Shell Electron Pair Repulsion VSEPR

Acetylene C2H2

The geometry of the molecule is linear and the bond angle = 180°.

H C C HH C C H

Two groups of electrons - one of two and one of 6 electrons.Molecule is linear

CH5N 

NC

H

H

H H

H

Geometry around nitrogen ?Geometry around carbon

CH5N 

NC

H

H

H H

H

Geometry around nitrogen ?Geometry around carbon

The carbon atom is surrounded by three hydrogen atoms and one N.

The Nitrogen has a lone pair is attached to one carbon and two hydrogens.Therefore, we would predict that the carbon would have tetrahedral geometry

and is sp3 hybridized, the same for nitrogen.

C2H6O

There are two plausible Lewis or Line Bond structures. Both are acceptable structures.

H3C O CH3 H3C CH2 O H

C2H6O

There are two plausible Lewis or Line Bond structures. Both are acceptable structures.

H3C O CH3 H3C CH2 O H

The carbon atom is surrounded by three

hydrogen atoms and one O.

The Oxygen has two lone pairs and is

attached to two carbons.

Therefore, we would predict that the

carbon would have tetrahedral geometry

and is sp3 hybridized, the same for

oxygen with two lone pairs and two bonds

to different carbon atoms.

The carbon atoms all surrounded by 4

groups .

The Oxygen has two lone pairs and is

attached to one carbon and one hydrogen

atom.

Therefore, we would predict that the

carbon atoms would have tetrahedral

geometry and are sp3 hybridized, the

same for oxygen with two lone pairs and

two bonds to different carbon atoms.

Benzene C6H6 

H H

HH

H H

Geometry at this carbon?

Benzene C6H6 

H H

HH

H H

Geometry at this carbon?

Each carbon has an identical set of groups surround it.

one hydrogen one C-C double bond and one C-C single

bond for a total of 3 groups. Therefore, we would predict

that each carbon would be planar and sp2 hybridized

Acetonitrile C2H3N

Lewis structure?Hybridization?Shape?