Hybridization Theory

 When applying the concepts of

Valence Shell Electron Pair Repulsion Theory ,

also known as VSEPR Theory, to covalent systems it becomes possible to predict the geometry of the atoms within the structures and the geometry of the molecules, overall.Through this process, structures are found to exist in a variety of geometric patterns. Some systems are linear, others trigonal planar and still others are tetrahedrons.

In trying to apply the predicted geometric patterns to the atoms used to make the molecules, problems arise.

• All atoms, under normal conditions, use valence level s and p orbitals. These orbitals exist with shapes that are incompatible with the predicted geometric patterns from VSEPR Theory.
• Tetrahedral geometry consists of a series of positions that are arranged at angles of 109.5⁰, when measured from an external position to a central position to an external position. At best, it is difficult to imagine the p orbitals, with angles between them of 90⁰, altering their own structures to accommodate the required tetrahedral angles.
• The trigonal planar structures have angles of 120⁰. Again, how is it possible for a set of valence s and p orbitals to accommodate the structural requirements of the trigonal planar structures?

In order to explain the existence of the structures of atoms and molecules that correspond to the geometric patterns predicted from VSEPR Theory, chemists have found it necessary to develop Hybridization Theory.

Hybridization Theory says that atoms involved in the formation of covalently bonded molecules will undergo structural changes in their valence level atomic orbitals. They will convert their atomic orbitals into a new set of orbitals called Hybrid Orbitals. The Hybrid Orbitals will have some characteristics of the original atomic orbitals, but differ somewhat in their geometric configurations. Hybridization Theory is a variation of Molecular Orbital Theory.

In biology, the word "hybrid" usually refers to a genetic mixing.

• In that context, two items are genetically crossed to produce a new system that has some of the characteristics of the original systems, but also has created additional characteristics that will be unique to it. The concept of hybridizing orbitals is very similar.
• In this process, new orbitals will be formed that contain some of the qualities of the original orbitals, but the new orbitals will also have qualities that are unique to them and better serve the needs of the system. When orbitals are hybridized a fundamental rule to bear in mind is that the number of hybrid orbitals formed will always equal the number of original atomic orbitals that were involved in the hybridization process.

Definition: Hybridization is the process of combining two or more atomic orbitals to create new orbitals, called hybrids, that will fulfill the geometric demands of the system.

Definition: Group is the term used to represent a bonded atom or nonbonded electron pair that is attached to a given atom. In determining the types of hybrid orbitals that an atom has, it is essential to first determine the number of groups around that atom. For basic hybridization theory, atoms will generally be surrounded by two groups, three groups, or four groups.