# what is hybridisation and what are its applications?

### Asked by | 14th Jun, 2008, 03:13: PM

Covalent bonds are formed when atomic orbitals overlap. There are two types of orbital overlap that an organic chemist needs to be familiar with. **Sigma, s, overlap** occurs when there is one bonding interaction that results from the overlap of two orbitals. **Pi, p, overlap **occurs when two bonding interactions result from the overlap of orbitals. The organic chemist also needs to realise how these orbital overlaps relate to the type of bonding that is occuring between atoms:

single bondIf one tries to correlate the overlap of atomic orbitals to the shape of a molecule, however, the expected geometry does not correspond to a maximum orbital overlap. Take a look at methane, CHsoverlap

double bondsandpoverlaps

triple bondsand twopoverlaps

_{4.}VSEPR predicts a tetrahedral geometry about the carbon atom but this is not achieved when one considers a maximum orbital overlap between four 1s orbitals of H and the 2s, 2p

_{x}, 2p

_{y}and 2p

_{z}orbitals of carbon.

**Hybridisation**is a solution to this problem. It is the imaginary mixing of the 2s, 2p

_{x}, 2p

_{y}and 2p

_{z}atomic orbitals of carbon to form a new set of

**'hybrid' orbitals**that orient themselves in the desired VSEPR geometry. The hybrid orbitals are equivalent to one another making all orbital overlaps equivalent, therefore, all C-H bonding interactions equivalent. Hybrid orbitals are named by considering the type and number of atomic orbitals from which they arose. For CH

_{4}then the hybridisation for the carbon is sp

^{3}.

**Hybrid orbitals are responsible for all the**

*One sees that the hybridisation of an atom can be determined very quickly by considering the number of electron groups about an atom.***s**bonding overlaps in a molecule.

**Unhybridised orbitals are responsible for all the**

**p**bonding overlaps in a molecule.

Consider a molecule of carbon monoxide, CO. Start by visualising the imaginary mixing of the valence atomic orbitals of carbon. To do this refer to the valence orbital energy level diagram of carbon, the number of electrons is determined by taking into account any formal charges. In CO, carbon has a formal charge of one so that the electron configuration is 2s^{2}2p^{3}, rather than 2s^{2}2p^{2}.

Next the number of groups about carbon for which hybridisation must occur is considered. It has two electron groups, one bonding the other a lone pair.

The number of electrons groups is saying that two atomic orbitals must hybridise. Orbitals are always hybridised from lowest to highest energy, therefore, one s and one p orbital will hybridise. The energy level diagram will change so that the two hybridised orbitals will become equal in energy, which will be an average of the energy for the atomic orbitals from which they arose, and two unhybridised p orbitals remain.

The energy level diagram for the oxygen is determined in the same way but the electron count will take into consideration the 1+ formal charge.

Recall that CO has a triple bond, which should be the result of one s and two p overlaps. The hybrid orbitals are involved in forming the s overlap of the triple bond and in housing the lone pairs of electrons. The unhybridised p orbitals are involved in two p overlaps, which will be located perpendicular to one another.

### Answered by | 14th Jun, 2008, 09:57: PM

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