1.

Explain periodicity of valence or oxidation states and explain Na_(2)O " and " OF_(2).

Answer»

Solution :The valence is the most characteristic property of the elements and can be understood in terms of their electronic configurations.
Ex. : In `OF_(2)` OXYGEN `(+2)` but in `Na_(2)O`oxygen is `( -2)`.
EXPLANATION in `OF_(2)"and "Na_(2)O` :
The order of electronegativity of the three elements involved in these compounds is `F gt O gt Na`.
Each of the atoms of fluorine, with OUTER electronic configuration `2s^(2)2P^(5)`, shares one ELECTRON with oxygen in the `OF_(2)` molecule.
Being highest electronegative element, fluorine is given oxidation state` -1`.
There are two fluorine atoms in this molecule, oxygen with outer electronic configuration `2s^(2)2p^(4)` shares two electrons with fluorine atoms and thereby exhibits oxidation state `+2`.
In `Na_(2)O`,oxygen being more electronegative accepts two electrons, one from each of the two sodium atoms and, thus, shows oxidation state` -2`.
On the other hand sodium with electronic configuration `3s^(1)`loses one electron to oxygen and is given oxidation state `+1`.
So in `Na_(2)O " and " F_(2)O`compound oxidation number of oxygen is `(-2)" and " (+2)` respectively.


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