KOSSEL - LEWIS APPROACH TO CHEMICAL BONDING - Octet rule

KOSSEL - LEWIS APPROACH TO CHEMICAL BONDING (Octet rule)

     ·       Every atom has a tendency to complete its octet in outermost shell

     ·       H has the tendency to complete its duplet.

     ·       To acquire inert gas configuration atoms loose or gain electron or share electron.

      ·       The tendency of atoms to achieve eight electrons in their outer most shell is known as Lewis octet rule.

Exception of Octet Rule

(a) Incomplete octet molecules: - or (electron deficient molecules): -

·    Compound in which octet is not complete in outer most orbit of central atom.

 Example - 

Halides of IIIA groups, BF3, AlCl3, BCl3

hydride of III A/13th group etc.

Other examples – BeCl2 (4e),

(b) Expansion of octet or (electron efficient molecules)

Compound in which central atom has more than 8e– in outermost orbits.

 Example - In PCl5 , PF5,SF6 and IF7 the central atom P, S and contain 10, 12, and 14 electrons respectively.

(c) Odd electron molecules: - Central atom in a molecule has an unpaired electron or odd no of electrons in their outer most shell. e.g. NO, NO2, ClO2 etc.

d). It is based upon chemical inertness of noble gases. However, Xe and Kr also combine with other to form compound likes XeF₂, KrF₂, XeOF₂ etc.

E) could not explain relative stability of molecules

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