Question

9. Why does the reaction of a small amount of bromine with graphite convert the semiconductor to a metallic conductor, but the reaction of bromine with sodium converts the metal into an insulator

Answer 1

Graphite is semi conductor because it contain free electrons due to SP2 Hybridisation . Graphite contain two dimensional layer structure, when inter act with Bromine , Bromine( bromide ions) occupied internal gaps or space and increase pressure on layers. So that graphite atoms exert pressure on each other so that become conductor and increase conductivity.

But in case of sodium metal it contain close packed structure, so that Bromine interact with Na metal become insulator( ions are fixed in their close packing ).