Hybridisation – Mixing Up Orbitals with sp, sp2, sp3

Essentially, hybridisation is the mixing of standard atomic orbitals to form new orbitals – which can be used to describe bonding in molecules.

Most importantly we have sp3, sp2 and sp hybridisation.

sp3 Hybridisation in Methane (CH4):

The best way I can describe sp3 hybridisation is in Methane (also the most basic choice!). This is simplified for expression. Remember that Carbon has 6 electrons.

  • In methane (CH4), 1 Carbon binds with 4 Hydrogens. The carbon atom itself has only 2 electrons available for bonding in the 2p subshell.

    Carbon - Ground (normal) electron states. 1s2, 2s2, 2p1 2p1.

  • In order for 4 hydrogens to bind there need to be 4 electrons available for bonding, which cannot be achieved at the moment. The pull of a hydrogen nucleus results in an electron being excited from the 2s subshell into the 2p subshell, where it is available for bonding.

    Carbon - An electron has been excited to the 2p orbital.

    Carbon - An electron has been excited to the 2p orbital.

  • This excitation changes the forces on the valence (bonding) electrons as the nucleus now exerts a stronger effective core portential upon them. This and other factors leads to the creation of a new ‘hybridised orbital’, called sp3.
    Carbon - Hybridisation forms SP3 orbital.

    Carbon - Hybridisation forms sp3 orbital.

    This leaves 4 valence electrons which will each overlap with the s orbital of a Hydrogen to form a σ (sigma) bond. These hydrogens space themselves as far apart as possible, leading to the tetrahedral structure of methane.

    3D animation of methane.

    3D animation of methane. Produced on ChemSketch.

    Each of the bonds in the image above are σ-bonds.

    Methane Hybridisation. Shows the S orbits of H overlapping with SP3 orbitals of C. Note 2 electrons in each bond, one from carbon and one from hydrogen. Image by K. Aainsqatsi, released into public domain.

    Methane Hybridisation. Shows the S orbits of H overlapping with sp3 orbitals of C. Note 2 electrons in each bond, one from carbon and one from hydrogen. Image by K. Aainsqatsi, released into public domain.

sp2 Hybridisation in Ethene (C2H4):

This is similar to sp3 hybridisation, except there are only 2 hydrogen nuclei pulling on the bonding electrons (which need an electron each) and the other 2 electrons are required for the π (pi) bond (double bond) between the two Carbons.

A molecule of Ethene.

A molecule of Ethene.

The electron configuration in carbon starts the same:

Carbon - Ground (normal) state of electrons

then:

Carbon - An electron has been excited to the 2p orbital.

Carbon - An electron has been excited to the 2p orbital.

but the resulting spread is different:

Carbon hybridisation in Ethene (sp2)

Carbon hybridisation in Ethene (sp2)

Only 2 of the 2p orbitals are used in sp2 hybridisation; in contrast to the 3 used in sp3 hybridisation (you should be seeing where the numbers come from!).

This leaves us with 3 sp3-orbitals and 1 p-orbital to bond with. 2 of the sp3 orbitals are used for forming σ-bonds with the 2 hydrogens, while the remaining sp3 orbital binds with the other carbon to form a σ-bond and the p-orbital bonds with a p-orbital from the other carbon to form a π-bond.

Every double bond (regardless of what atoms it joins) consists of a π-bond and a σ-bond.

Shows seperate carbon atoms in sp2 hybridisation, then combined to form ethene.

Shows seperate carbon atoms in sp2 hybridisation, then combined to form ethene.

sp Hybridisation in Ethyne (C2H2):

This can occur on an atom with a triple bond such as the alkynes. Ethyne is the simplest.

Ethyne. Triple bonded Carbon with 2 hydrogens.

Ethyne. Triple bonded Carbon with 2 hydrogens.

In this case we only have 1 hydrogen attached to a carbon, and three bonds between each carbon.  That’s 1 hybridised bond between the carbon and hydrogen with another hybridised bond between the carbons. The other two p-orbitals form two more bonds between the carbons.

Ethyne - sp Hybridisation

Ethyne - sp Hybridisation

This essentially means that the triple bond consists of 1 σ-bond and 2 π-bonds.

Summary:

Essentially, the hybridisation of the carbon atom is based on the number of bonds to other carbons or identical atoms.
sp3 = single bond
sp2 = double bond
sp = triple bond

9 thoughts on “Hybridisation – Mixing Up Orbitals with sp, sp2, sp3

  1. vyy

    Thank you so much for your explanation. It is much clearer than my textbook and teacher’s explanation! Really nice diagrams too :]

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