CLASS :- 11
Topic :- octet rule
octet rule and mode of chemical combination
In 1916 W. kossel and G.N.Lewis Develop important theory of chemical combination between atom now as electronic theory of chemical bonding
According to this concept atom achieve stable noble gas configuration either by transfer of valence electron from one atom to another or by sharing of valency electron Between atoms
according to this concept all atom try to stable noble gas configuration means they try to 8 electrons in their respected valency cell and now new concept introduced It is called octet rule
In the light of octet rule sodium magnesium and Aluminium in the third period of the periodic table loss electron from valency cell and form positive ions that have the same electronic configuration as neon(1s2 ,2s2,2p6)
On the other hand fluorine oxygen and nitrogen gain electrons and form negative ions that have same electronic configuration as neon(1s2 ,2s2,2p6)
In the light of octet rule w kossel Observe that
halogen family , glycogen family form negative ions and alkali metal , alkaline earth metal loss of electrons to form a positive ions means these ion formed by the gain or loss of electron by their respective atom
The negative and positive ions have stable electronic configuration means that have 8 electron in their respective outer cell
octet rule and exceptions or Drawbacks of the the octet rule
1 Hydrogen molecules :- In hydrogen molecules, Each hydrogen atom have 1 s 2 electronic configuration therefore octet is not needed to achieve a stable configuration Because first cell has only two electrons
2 incomplete octet of the central atom :- in Beryllium chloride Boron trifluoride Aluminium trichloride Boron hydride And beryllium hydride molecules Centre atom does not have complete octet but All molecules stable in nature.
3 expanded octet of the centre atom :- Phosphorus In Phosphorus pentachloride , Sulphur in sulphur hexafluoride , Iodine in Iodine heptafluoride molecules has more than 8 electron . in
4 odd electron molecules :- In nitric oxide and Nitrogen dioxide molecules have odd number of electrons
5 formation of xenon compound with oxygen and fluorine
generally noble gas element chemically inert in a nature but xenon form various compound with oxygen and fluorine as XeF2 , XeF4 , XeF6 , XeOF2 ,
XeOF4 , XeO3 and XeO4
6 This Concept does not explain stability and shape of molecules