`=>` In order to explain the formation of chemical bond in terms of electrons, in 1916, Kössel and Lewis succeeded independently in giving a satisfactory explanation.
● They were the first to provide some logical explanation of valence which was based on the inertness of noble gases.
`color{green}("Postulates :")`
(i) Lewis pictured the atom in terms of a positively charged ‘Kernel’ (the nucleus plus the inner electrons) and the outer shell that could accommodate a maximum of eight electrons.
(ii) These eight electrons occupy the corners of a cube which surround the ‘Kernel’.
● Thus the single outer shell electron of sodium would occupy one corner of the cube, while in the case of a noble gas all the eight corners would be occupied.
● This octet of electrons, represents a particularly stable electronic arrangement.
(iii) Lewis postulated that atoms achieve the stable octet when they are linked by chemical bonds.
● In the case of sodium and chlorine, this can happen by the transfer of an electron from sodium to chlorine thereby giving the `Na^+` and `Cl^–` ions.
● In the case of other molecules like `Cl_2`, `H_2`, `F_2`, etc., the bond is formed by the sharing of a pair of electrons between the atoms.
● In the process each atom attains a stable outer octet of electrons.
`color{green}("Lewis Symbols :")` In the formation of a molecule, only the outer shell electrons take part in chemical combination and they are known as valence electrons.
● The inner shell electrons are well protected and are generally not involved in the combination process.
● G.N. Lewis, an American chemist introduced simple notations to represent valence electrons in an atom. These notations are called Lewis symbols.
● For example, the Lewis symbols for the elements of second period are as given in fig.
`=>` In order to explain the formation of chemical bond in terms of electrons, in 1916, Kössel and Lewis succeeded independently in giving a satisfactory explanation.
● They were the first to provide some logical explanation of valence which was based on the inertness of noble gases.
`color{green}("Postulates :")`
(i) Lewis pictured the atom in terms of a positively charged ‘Kernel’ (the nucleus plus the inner electrons) and the outer shell that could accommodate a maximum of eight electrons.
(ii) These eight electrons occupy the corners of a cube which surround the ‘Kernel’.
● Thus the single outer shell electron of sodium would occupy one corner of the cube, while in the case of a noble gas all the eight corners would be occupied.
● This octet of electrons, represents a particularly stable electronic arrangement.
(iii) Lewis postulated that atoms achieve the stable octet when they are linked by chemical bonds.
● In the case of sodium and chlorine, this can happen by the transfer of an electron from sodium to chlorine thereby giving the `Na^+` and `Cl^–` ions.
● In the case of other molecules like `Cl_2`, `H_2`, `F_2`, etc., the bond is formed by the sharing of a pair of electrons between the atoms.
● In the process each atom attains a stable outer octet of electrons.
`color{green}("Lewis Symbols :")` In the formation of a molecule, only the outer shell electrons take part in chemical combination and they are known as valence electrons.
● The inner shell electrons are well protected and are generally not involved in the combination process.
● G.N. Lewis, an American chemist introduced simple notations to represent valence electrons in an atom. These notations are called Lewis symbols.
● For example, the Lewis symbols for the elements of second period are as given in fig.