Some Important Points About Hybridisation:
- Orbitals having
approximately equal energies and which belong to the same atom or ion
can undergo hybridisation.
- Number of hybrid orbitals
produced is equal to number of atomic orbitals mixed.
- It is not essential for all
half-filled orbitals to participate in hybridisation. Also, it is not
necessary that only half-filled orbitals should participate in
hybridisation. Completely filled orbitals with different energies can
- Hybridisation never takes
place in isolated atoms but occurs only at the time of bond formation.
- Type of hybridisation
indicates the geometry of the molecule. One can tell the shape of the
molecule by knowing the type of hybridisation.
- Geometry or Shape of Molecule: A particular arrangement
obtained by bonding a number of atoms in definite direction to the
central atom of a molecule is called the geometry or the shape of the
- Experimental Methods: Different experimental
methods to determine the shape of molecule have been deviced since the
last 40 years. These methods are:
(i) Spectroscopic Methods: The emission and absorption of
electromagnetic radiations by the molecules form the basis for these
(ii) Diffraction Methods: Scattering of X-rays, electron beams
and neutron beams form the basis for these methods.
- Theoretical Methods:
geometry and shape of a molecule can be explained on the basis of:
(ii) Valence Shell Electroin Pair Repulsion Theory (VSEPR Theory).
This theory was proposed by Sidgwick and Powell in 1940. The basic
concept of this theory is as follows:
The central atom is linked to other atoms by covalent bonds which are
formed by sharing of electrons. The central atom is surrounded by a pair
of electrons and also lone pair of electrons.
The stability of a molecule means that it should have minimum energy. If
the electron pair surrounding the central atom are nearer, they will
repel each other, hence, energy of the molecule
will increase. But if electron pair are far apart, the energy of the
molecule will be low.
Hence, the electron pair surrounding the central atom repel each other
and move away from each other, so that there is no repulsion between
them. Hence, the molecule has minimum energy and maximum stability. This
concept is called the Valence Shell Electron Repulsion Theory.
The electron pairs then take up definite positions around the central
atom to give the molecule a definite shape and geometry. This concept
helps to define the shape and geometry of the molecule.
(1) Shape of the molecule containing two atoms is always linear.
(2) For molecules which have 3 or more atoms, one of the atom is called the central atom to which other atoms
(3) When a central atom is linked to similar atoms, and is surrounded by
bond pair of electrons, repulsions between them are similar. Hence, the
shape of a molecule is symmetrical and the molecule is said to have a
(4) When the central atom is linked to different atoms and is surrounded
by a bonding pair as well as a lone pair of electrons, the
repulsion between them is different. The molecule is then said to have
an irregular or distorted geometry.
(5) The shape of the molecule depends on the total number of electron
pairs present around the central atom.