Orbital Hybridizations & Molecular Shapes

14.2.3

14.2.3 Identify and explain the relationships

between Lewis structures, molecular shapes and types of hybridization (sp, sp2 and sp3).

We’ll start with a quick review of hybridization…ATOMIC ORBITALS OVERLAP TO FORM 2

TYPES OF COVALENT BOND:○ δ and π

Bond Orders & Hybridization Single Bond = sp3 hybridization

A δ bond

Double Bond = sp2 hybridizationA δ bond + a π bond

Triple Bond = sp hybridizationA δ bond + 2 π bonds

Hybridization & Geometry

If an s orbital is sphere shaped and 3 p orbitals are dumbbell shaped and at 90˚ to each other, they clearly must undergo some change to get 4 sp3 orbitals that are at 109˚ to each other.Hybrid orbitals are not only used to explain the

appearance of degenerate orbitals.They also can be used to explain the

geometries predicted by VSEPR theory.

+ =

Sigma (δ) Bonds Remember that sigma bonds are

formed between 2 s orbitals and have linear/axial symmetry.

Pi (π) bonds When a sigma bond is formed by direct orbital

overlap and this brings two parallel 'p' orbitals into close proximity then these can overlap sideways (laterally) to form a region of electron density that is not directly between the two nuclear centers but which nevertheless contributes to bonding. This is called a pi bond.

Why hybridize?

It seems that the orbitals used for bonding are arranged as far apart as possible suggesting that they have the same energy (degenerate). We know that the orbitals on the carbon atom do not have the same energythe 2s orbital is of lower energy that the

three 2p orbitals.

Why hybridize?

Hybridisation is a model that allows us to combine the atomic orbitals and then produce four degenerate orbitals to be used for bonding.

Why hybridize?

In order for the electrons to be ready for this process one of them must be promoted from the 2s orbital to the 2pz orbital as in the diagram.

The sp3 hybrid orbital

As these new orbital have emerged from one s and three p orbitals they are called 'sp3' orbitals.

Other types of hybridization Carbon can also bond to three other

atoms instead of four (as in methane) and it seems that it hybridised its orbitals using only the 2s and two of the 2p orbitals to do this.

Other types of hybridization How would an sp hybridization work?

Hybridization & Geometry

Now that we’ve looked at the hows and whys, it is time to try and visualize…

See the animations below. http://ibchem.com/IB/ibnotes/full/bon_htm/hybrid.htm

The following slides show the combinations of atomic orbitals giving rise to each type of bond.

s overlapping an s

Type of bond = sigma Example = H-H in H2

s overlapping a p

Type of bond = sigma Example = H-Cl in HCl

p and p end-on

Type of bond = sigma Example = Cl-Cl in Cl2

hybrid orbitals and an s

Type of bond = sigma Example = C-H in CH4

hybrid orbitals with hybrid orbitals

Type of bond = sigma Example = one of the C=C in C2H4

p and p sideways

Type of bond = pi Example = the other C=C in C2H4