Directional Property of the Covalent Bond

The orbital overlap

The sharing of orbitals between two atoms is possible only when the atoms are close enough to overlap their orbitals. Thus, orbital overlap is necessary for the sharing of electrons and bond formation. With the orbitals coming close together, there is an increase in the electron density between the two nuclei. This lowers the repulsion between the two nuclei and the two nuclei stay together to form a bond.

When two atoms of the same kind share a pair of electron, the shared pair of electrons lie mid way between the two atoms because the electron density between the two nuclei is symmetrical. The two identical atoms share the electron pair equally. When the electron pair is shared between two different atoms, the electron density is not symmetrical between the two nuclei. In such a case, the shared pair of electrons lie closer to more electronegative atom. As a result the sharing of electron pair between the two atoms is not equal.

Types of overlapping

Various type of atomic orbital overlap leads to covalent bond formation.

• 's-s' overlap

The half filled 's' orbitals overlap each other.

• 's-p' overlap

A half filled 's' orbitals of one atom overlaps with one of the 'p' orbitals having only one electron.

'p-p' overlap along the orbital axis

Two half filled 'p' orbitals overlap along the line joining the two nuclei. This is also called as head on, end on or end to end linear overlap.

• p-p sideways overlap

Two half filled 'p' orbitals overlap along the line perpendicular to the nuclear axis. The overlapping of the 'p' orbitals is parallel to each other. This is also called as lateral overlap.

Fig: 6.3 - The s-s overlap, s-p overlap, p-p overlap along the orbital axis and p-p sideways overlap