Hybridization: Definition, Orbitals & Explanation

Hybridization is the mixing of atomic orbitals. The background for this is that in reality bonds between atoms often occur differently than one would expect theoretically.

The orbital model

Because the electrons of molecules do not revolve around the nucleus at specific points, there is the orbital model. This indicates the area in which the electrons are most likely to be found.

There are always two electrons in an orbital. Each electron has a specific energy content. This results in the different spatial shape of the orbital. The spatial form is always symmetrical.

There are different orbitals, distinguished by their energy level:

• The s orbital has 1 orbital at its energy level and contains a maximum of 2 electrons. S orbitals are spherical.
• The p orbital contains 3 orbitals at the same energy level and contains a maximum of 6 electrons. There are 3 p orbitals which are dumbbell shaped. They are spatially directed, which is why they are also known as -, – and – orbitals.
• The d orbital contains 5 orbitals at the same energy level and contains a maximum of 10 electrons. There are 5 d orbitals, 4 of which are rosette shaped and one is dumbbell shaped with an additional ring.
• The f orbital contains 7 orbitals at the same energy level and contains a maximum of 14 electrons. There are 7 f orbitals.

Chemical bond types

When the different orbitals overlap, bonds are formed between molecules. Depending on how the electrons are distributed, one speaks of one sigma or pi bond.

Sigma bond

At a sigma bonding is the charge distribution of the electrons in the compound rotationally symmetric to the bond axis. Three-dimensional objects are rotationally symmetrical. This means that rotation by any angle will image the same object.

In order for this type of bond to form, the electron clouds of the bonding partners must have a large overlap. As a result, sigma bonds are energetically stable. A sigma bond forms when two s, two p, or one s and one p orbital join together. The different types of overlap are shown visually in Figures 1 to 3.

Figure 1: Connection of 2 s orbitals

Figure 2: Connection of an s and a p orbital

Figure 3: Connection of 2 p orbitals

Pi Binding

the pi bond arises from an overlap of d and p orbitals. It is not rotationally symmetrical. The charge is distributed below and above the sigma bond. In pi bonding, two p orbitals overlap perpendicularly.

Figure 4: Perpendicular connection of 2 p orbitals

Different types of hybridization

sp hybridization

As the name suggests, an s and a p orbital merge here. A linear, club-shaped hybrid orbital is formed with an angle of 180°.

Figure 5: sp hybrid orbital

-Hybridization

With the alkene propene (C3H6) there is a – hybridization. That is, hybridization of one s orbital and two p orbitals occurs. This results in three energetically equivalent hybrid orbitals. A p orbital remains in the ground state. This forms a double bond between two carbon atoms and single bonds with the hydrogen atoms.

Here the angle between the orbitals is 120° – this angle reflects the energetically most favorable spatial arrangement of the electrons.

Figure 6: sp2 hybrid orbital

-Hybridization

The -hybridization can be represented well on the alkane methane (CH4). The element carbon (C) has two outer electrons. Normally, this element would only bond with 2 H atoms. In the case of methane, however, there are four equivalent bonds. They are indistinguishable from each other.

The reason for this is hybridization: a spherical carbon s and three dumbbell p orbitals combine – forming 4 club-shaped hybrid orbitals.

These orbitals are slightly lower in energy than the p but slightly higher than the original s orbital. Because of this, each hybrid orbital has one electron and can bond with one hydrogen atom at a time.

This reduces the total energy of the entire molecule. Accordingly, methane takes on the external form of a tetrahedron. This results in an angle of 109.5° between the orbitals.

Figure 7: sp3 hybrid orbital

Hybridization in Biochemistry

In biochemistry, hybridization means the formation of complementary DNA single strands to already existing ones. Two single strands of DNA become a double strand. This hybridization can only take place if both single strands have complementary bases. The key mechanism here is hydrogen bonding.