Sn, C, and Si, Ge are all group XIV elements. Yet, Sn is a conductor, C is an insulator while Si and Ge are semiconductors. Why?

Explanation

Because (i) in the structure of Sn, energy bands are superposed on each other, so energy gap between them is zero and hence Sn is a good conductor of electricity. (ii) In the structure of C, energy gap is 5.4 eV which is comparatively quite large and so it becomes non-conductor of electricity. (iii) Energy gaps in Si and Ge are respectively 1.1 eV and 0.7 eV which are moderate and so their conductivity is less than good conductors but more than non-conductors. Hence, Si and Ge become semiconductors.