Question -
Answer -
The octet rule or theelectronic theory of chemical bonding was developed by Kossel and Lewis.According to this rule, atoms can combine either by transfer of valenceelectrons from one atom to another or by sharing their valence electrons inorder to attain the nearest noble gas configuration by having an octet in theirvalence shell.
The octet rulesuccessfully explained the formation of chemical bonds depending upon thenature of the element.
Limitations of the octet theory:
The following are thelimitations of the octet rule:
(a) The rule failed topredict the shape and relative stability of molecules.
(b) It is based upon the inert nature ofnoble gases. However, some noble gases like xenon and krypton form compoundssuch as XeF2, KrF2 etc.
(c) The octet rule cannot be applied to theelements in and beyond the third period of the periodic table. The elementspresent in these periods have more than eight valence electrons around thecentral atom. For example: PF5, SF6, etc.
(d) The octet rule is not satisfied for allatoms in a molecule having an odd number of electrons. For example, NO and NO2 donot satisfy the octet rule.
(e) This rule cannot be applied to thosecompounds in which the number of electrons surrounding the central atom is lessthan eight. For example, LiCl, BeH2, AlCl3 etc. donot obey the octet rule.
