Hybridization — sp, sp2, sp3, sp3d & sp3d2

Hybridization is a model used in introductory chemistry to connect a Lewis structure to the local geometry around one atom. In most first-year problems, you count electron domains around that atom and match the count to a label such as $sp$, $sp^2$, or $sp^3$.

The usual shortcut is 2 domains $\rightarrow$ $sp$, 3 $\rightarrow$ $sp^2$, 4 $\rightarrow$ $sp^3$, 5 $\rightarrow$ $sp^3d$, and 6 $\rightarrow$ $sp^3d^2$. That shortcut is very useful in general chemistry, but it works best as a simple local model, not as a final description of every bonding situation.

Hybridization chart: $sp$, $sp^2$, $sp^3$, $sp^3d$, and $sp^3d^2$

Electron domains around one atom	Usual hybridization label	Usual electron-domain geometry
2	$sp$	linear
3	$sp^2$	trigonal planar
4	$sp^3$	tetrahedral
5	$sp^3d$	trigonal bipyramidal
6	$sp^3d^2$	octahedral

For this count, a single bond, double bond, triple bond, or lone pair each counts as one domain. That condition matters because multiple bonds are often overcounted.

What the labels mean

The label tells you how many orbitals are mixed in the introductory model for one atom:

• $sp$: one $s$ and one $p$
• $sp^2$: one $s$ and two $p$
• $sp^3$: one $s$ and three $p$
• $sp^3d$: one $s$, three $p$, and one $d$ in the usual general chemistry picture
• $sp^3d^2$: one $s$, three $p$, and two $d$ in the usual general chemistry picture

In practice, students usually use these labels as a quick bridge from a Lewis structure to geometry.

How to determine hybridization from a Lewis structure

Start with the atom you care about.

1. Draw a reasonable Lewis structure.
2. Count electron domains around that atom.
3. Treat each bond region as one domain, even if it is a double or triple bond.
4. Count each lone pair as one domain.
5. Match the total to the hybridization chart.

This is why hybridization and VSEPR often line up in introductory problems: both rely on the same domain count.

Worked example: why carbon in $C_2H_4$ is $sp^2$

In ethene, $C_2H_4$, each carbon is bonded to two hydrogens and to the other carbon by a double bond.

Now count electron domains around one carbon:

• two $C-H$ single bonds $\rightarrow$ 2 domains
• one $C=C$ double bond $\rightarrow$ 1 domain

That gives 3 electron domains total, so the carbon is labeled $sp^2$ in the introductory model.

The same count also predicts a trigonal planar arrangement around each carbon. This example is useful because it shows the rule students miss most often: the double bond counts as one domain, not two.

Common mistakes when finding hybridization

Counting a multiple bond as more than one domain

For hybridization counting, one double bond is one domain and one triple bond is one domain.

Forgetting lone pairs

Lone pairs count too. An atom with three bonds and one lone pair has 4 domains, which often gives an $sp^3$ label in this model.

Mixing up local geometry and whole-molecule shape

Hybridization is assigned to one atom at a time. It describes the local arrangement around that atom, not the overall shape of the entire molecule.

Treating every hybridization label as equally reliable in advanced bonding cases

In general chemistry, labels such as $sp^3d$ and $sp^3d^2$ are standard shortcuts for 5 and 6 electron domains. In more advanced courses, some hypervalent molecules are described with other bonding models, so the shortcut should be treated as a course-level model, not a universal rule.

When hybridization is most useful

Hybridization helps most when you want to connect a Lewis structure to a local geometry, expected bond angles, or the idea that a double bond usually contains one $\sigma$ bond and one $\pi$ bond.

It helps less when bonding is strongly delocalized or when a simple localized Lewis structure is already a weak description.

Try a similar molecule

Try your own version with $CO_2$, $CH_4$, or $SF_6$. Count the electron domains around the central atom, assign the hybridization label, and then check whether the geometry from VSEPR tells the same story.