As shown on the Periodic Table, Carbon has a Ground State of [He] 2s22p2 as represented by this orbital diagram.

6C

Ground State

  2p2 2s2 [He]

 [He] 2s2 2p2

close

 [He]

Carbon

 [He] 

C2H4

NSF ATE DUE#1601612

A double bond (=) is made of one sigma (σ) bond and one pi (π) bond. =; 1σ +1π

Double Bonds: Ethene

Trigonal Planar

H

C

Notice there are only two singly occupied orbitals for bonding for each Carbon.

Promotion State

 [He]

 [He] 2s2 2p2

C2H4 bonds should all be equal, but remember that s bonds are stronger than p bonds, so nature has to do something to make the orbitals uniform. That something is hybridization.

To create equal bond strength, we mix different orbitals and create one set of uniform hybrid orbitals for each Carbon.

As shown on the Periodic Table, Hydrogen has a Ground State of 1s1

1H

Hydrogen

sp3

p, 1

 [He] 2s2 2p2

6C

p, 2

Hybridization State

p, 3

s

Hybrid Orbital

1

[He]

2

 [He] 2s2 2p2

3

An electron is promoted to create four singly occupied orbitals for bonding for each Carbon.

To make C2H4, we need 4 singly occupied orbitals to bond for each Carbon. 

4

Now that we have 4 uniform, singly occupied orbitals, we can bring in H to make Ethene.

π

C2H4

σ

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