Bond Hybridization

Chemistry: IB Diploma Higher Level, topic 2.7.3

Using VSEPR theory to predict bond angles can sometimes be problematic because the angles that are predicted do not match the orbital angles.

Valence bond theory predicts that the angle between the two O-H bonds is 90°, while VSEPR theory predicts an angle of 109.5°.
Experimental evidence shows that the bond angle is 104.5°.
To understand how molecules with more than two atoms form stable bonds, we require a more detailed model.

The difference in the predicted bond angles of water molecules is explained by the wave function in quantum mechanics.
The wave function, ψ, is a mathematical expression that contains information about each orbital and the wavelike properties of electrons in an isolated atom.
When atoms are bound together in a molecule, the wave functions combine to produce new mathematical descriptions that have different shapes.
The process of combining the wave functions for atomic orbitals is called hybridization.

The new orbitals that result are called hybrid orbitals.
These hybrid orbitals morph ‘s’ and ‘p’ orbitals into new equal hybrid orbitals which are part ‘s’ and part ‘p’.

Count the number of domains around the atom of interest:
Bonded domains + non-bonded domains.
The number of domains will be distributed to each type of orbital:
s = 1 orbital
p = 3 orbitals
d = 5 orbitals
f = 7 orbitals
The sum of the orbitals equals the number of domains.
Use the chart to help predict the hybridized orbitals and their corresponding bond angles.

Ethene has molecular formula C₂H₄.
Both carbons have three bonded domains, therefore the hybridization on each of the carbon atoms will be sp².
3 domains = 1 part s and 2 parts p, for a total of 3 equal hybridized orbitals.

Test yourself on Bond Hybridization