Sn, C, Si and Ge are all group XIV elements. Yet, Sn is a conductor, C is an insulator while Si and Ge are semiconductors. Why ?
Carbon dosent exist in free state it always form some compound due to its tatravaleny and some of the allotropes like grapite the structure allows one free electron and thus conduct electrcity where silicon when heat very temperture it does but carbon allotrope diamond have pure carbon but the bond is so strong to be broken thus require very high temperature to conduct electricity
The conduction level of any element depends on the energy gap between its conduction band and valance band. In conductors, there is no energy gap between conduction band and valance band. For insulator the energy gap is larger. For semiconductor the energy gap is moderate. The energy gap for Sn is 0ev, for C it is 5.4ev, for Si is 1.1ev and for Ge is 0.7ev related to there atomic size. Therefore Sn is a conductor,C is an insulator, Si and Ge are semiconductors.
If the valence and conditions bands overlap the substance is referred as a conductor for insulator rhe energy gap is large and fir semiconductor the energy gap is moderate the energy gap fir Sn is 0ev for C is 5.4ev Si is 1.1ev Ge is 0.7 ev acc. Their electrical conductivity varies