Saturday, May 14, 2011

Types of Covalent Bond

    It has already been discussed that the formation of a covalent bond involves the overlapping of half filled atomic orbitals. The covalent bond can be classified into two different categories depending upon the type of overlapping. These are:
    (a).    Sigma covalent bond.
    (b).    Pi covalent bond.
(a).    Sigma (σ) Bond
        This type of covalent bond is formed by the axial overlapping of half filled atomic orbitals. The atomic orbitals overlap along the inter-nuclear axis and involve end to end or head on overlap. The electron cloud formed as a result of axial overlap is cylindrically symmetrical about inter-nuclear axis. The electrons constituting sigma bond are called Sigma Electrons. There can be three types of axial overlap as discussed below:
  • s-s overlap
        It involves mutual overlap of half filled s-orbitals of the atoms approaching to form a bond. The bond formed so called s-s σ bond.
  • s-p overlap
        It involves mutual overlap of half filled s-orbitals of the one atom with half filled p-orbital of the other. The bond so formed is called s-p σ bond.
    p-p overlap

        It involves mutual overlap of half filled p-orbitals of the two atoms. The bond so formed is called p-p σ bond.

            The s-s, s-p and p-p overlaps have been shown diagrammatically as under:
    (b).    Pi (π) Bond

             This type of covalent bond is formed by the lateral or sidewise overlap of the atomic orbitals. The orbital overlap takes place in such a way that their axis is parallel to each other but perpendicular to the inter-nuclear axis. The pi bond consists of two charged clouds above and below the plane of the atoms involved in the bond formation. The electrons involved in the π bond formation are called π-electrons.
     



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