QUE WHAT IS F-CENTRE ? EXPLAIN THE FORMATION OF F CENTRE.

 SOL  F-CENTRE The holes occupied by electrons are called f centre (f -Farbe which means colour in German) which imparts colour in the compounds.

Formation Of F Centres When metal halides are heated in atmosphere of metal, anions from lattice leaves their lattice sites and diffuse into the surface. Anions combine with metals at the surface which releases electrons, that are trapped by the anion vacancies.                                                                                      

e.g. sodium vapours in NaCl imparts yellow colour. 

e.g. Potassium vapours in KCl imparts violet colour. 

e.g. Lithium vapours in LiCl imparts pink colour.