C,Si and Ge have same lattice structure.Why is C insulator while Si and Ge instinsic semiconductors?
Energy required to take out outer orbit electrons is less for Ge and Si but very large for C. so conduction electron is not easily available is not easily available for C and hence it is insulator .
The 4 bonding electronsof C, Si or Gelie, respectively,in the second , third and fourth orbit . Hence , energy required to take out and electron from these atoms (i.e., ionisation energy `E_(g ) `) will be least for Ge,following by Si and highest for C. Hence, number of free electrons for conduction in Ge and Si are significant but negligible small for C.