9.4. Hybridization of Atomic Orbitals http://www.ck12.org
FIGURE 9.37
In a molecule of hydrogen fluoride (HF),
the covalent bond occurs due to an over-
lap between the 1sorbital of the hydrogen
atom and the 2porbital of the fluorine
atom.The overlapping orbitals do not have to be of the same type. For example, in a molecule of HF, the 1sorbital of the
hydrogen atom overlaps with the 2porbital of the fluorine atom (Figure9.37).
In essence, any covalent bond results from the overlap of atomic orbitals. This idea forms the basis for a quantum
mechanical theory called valence bond (VB) theory.Valence bond theorystates that covalent bonds are formed by
the overlap of partially filled atomic orbitals.
Hybrid Orbitals
The bonding scheme described by valence bond theory must account for molecular geometries as predicted by
VSEPR theory. To do that, we must introduce a concept called hybrid orbitals.
Unfortunately, overlap of existing atomic orbitals (s,p, etc.) is not sufficient to explain some of the bonding and
molecular geometries that are observed. Consider the carbon atom in the methane (CH 4 ) molecule. An isolated
carbon atom has an electron configuration of 1s^22 s^22 p^2 , meaning that it has two unpaired electrons in its 2porbitals,
as shown below.
According to the description of valence bond theory so far, carbon would be expected to form only two bonds,
corresponding to its two unpaired electrons. However, methane is a common and stable molecule that contains four
equivalent CāH bonds. One way to account for this might be to promote one of the 2selectrons to the empty 2p
orbital.