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MHT-CET : Chemistry Entrance Exam

MHT - CET : Chemistry - Nature of Chemical Bond Know More

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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 also participate.
  • 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 molecule.
    .
  • 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 methods.
    (ii) Diffraction Methods: Scattering of X-rays, electron beams and neutron beams form the basis for these methods.
  • Theoretical Methods:
    The geometry and shape of a molecule can be explained on the basis of:
    (i) Hybridisation
    (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 are linked.
    (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 regular geometry.
    (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.

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