Hybridization

Hybrid Bonding Orbitals

Purpose

• In a previous lesson, you learned about the different atomic orbitals – s, p, d, and so on. When looking at a molecule such as methane, the atomic orbitals are not sufficient to describe the bonding and molecular geometry observed. The orbitals used for bonding are, therefore, different than the atomic orbitals. In the hybrid orbital bonding model, we take the atomic orbitals and combine them in a way that satisfies the behavior we see in molecules.

The problem with atomic orbitals.

• Carbon atom:– Valence Electron configuration 2s22p2

• Issue – only two unpaired electrons available for bonding; however, carbon can make four equivalent bonds.

– Orientation of the orbitals in the carbon atom• Issue – the p orbitals are 90o from one

another. In methane, the bonds arranged in a tetrahedral geometry at 109.5o from one another.

Solution – hybridize the orbitals

• Hybridization – a process in which different orbitals combine to make new equivalent orbitals with properties of both of the original orbitals

Hybridizationsp3 hybrid orbitals

Orbitals in the unbound carbon atom

Orbitals in the bound carbon atom

After this hybridization, carbon now has four equivalent orbitals that are used to bond to the hydrogens in

methane

Carbon with 4 bonds in methane (CH4)

C

H

HH

H

Arrangement of the hybrid orbitals in carbon

Designation of hybrid orbitals

• For methane, the s orbital and the three p orbitals from energy level two combined to make four equivalent orbitals called sp3 hybrid orbitals.

• Since four orbitals combined, we made four new orbitals• Other Combinations:

• One s and one p = two sp hybrid orbitals• One s and two p = three sp2 hybrid orbitals• One s and three p = four sp3 hybrid orbitals

• Note: The way we say an orbital such as sp3 is es pee three. Do not say es pee cubed.

Determining Hybridization is as easy as counting electron domains.

• The number of electron domains on an atom determines the number of hybrid orbitals required and thus the hybridization.

# of electron domains

# of hybrid orbitals

Hybridization of central atom

example

2 2 sp

3 3 sp2

4 4 sp3

C OO

Al

Cl

Cl Cl

O HH

Misconception alert!

• Hybrid orbitals can be used for both bonding and non-bonding electrons. This is why we need to count the number of electron domains, not just the number of bonds.

• Recall that a double and triple bond only count as a single domain. This does not change for determining hybridization.

Summary of Hybridization

Number of Electron Domains

Hybridization Drawing of hybrid orbitals

2 sp

3 sp2

4 sp3

Pause and Practice

• What is the hybridization on the following atoms?

– C in formaldehyde

– C in propyne

– N in nitrogen trifluoride

C

O

HH

C CH H

N

F

F F

Pause and Practice Answers

• What is the hybridization on the following atoms?

– C in formaldehyde• 3 domains on C• sp2 hybridization

– C in propyne• 2 domains on carbon• sp hybridization

– N in nitrogen trifluoride• 4 domains on N• sp3 hybridization

C

O

HH

C CH H

N

F

F F

Try the exercises