ELECTRON AFFINITY

ELECTRON AFFINITY

 The electron affinity of an atom is the amount of energy released when an electron is added in an empty or partially filled orbital of an atom in its valence shell to form an anion. 

Units 

It is expressed as KJ/mole.

e.g;                  F_(g)       + e^–                                            F ^– _(g)  E.A. =  – 348.8 KJ/mole

Along Period              Generally E.A. value increases from left to right in a period In A Group

            E.A. values decreases down the group.  

PECULIAR BEHAVIOUR OF Li 

This behaviour is due to following reasons

•      Both Li and Li⁺ ions have very small size

•      Li⁺ has high charge density 

•      Li has less electropositivity than sodium.

Differences

1.                  Li is much harder and lighter than the other alkali metals

2.                  Li can form stable complexes while other alkali metals do not have this property. e.g Li form Li(NH₃ )₄ .

3.                  Lithium hydride is more stable than hydrides of other alkali metals

4.                  Li is the least reactive of all the alkali metals