C and Si both have same lattice structure; having 4 bonding electrons in each. However, C is insulator where as Si is intrinsic semiconductor. This is because (a) In case of C the valence band is not completely filled at absolute zero temperature. (b) In case of C the conduction band is partly filled even at absolute zero temperature. (c) The four bonding electrons in the case of C lie in the second orbit, whereas in the case of Si they lie in the third. (d) The four bonding electrons in the case of C lie in the third orbit, whereas for Si they lie in the fourth orbit.

Answer: (c). C ( 1s² 2s² 2p²) has its four bonding electrons in the 2nd orbit; Si ( 3s² 3p²) has them in the 3rd orbit. Electrons in the 2nd orbit are closer to the nucleus and more tightly bound, so the band gap of C (about 5.4 eV) is much larger than that of Si ( 1.1 eV). Hence C is an insulator and Si a semiconductor. So the answer is (c).

C and Si both have same lattice structure; having 4 bonding electrons… | NEET 2012 (AIPMT, Prelims)

Q15NEET 2012 · AIPMT · PRELIMSMedium

Energy Bands in Solids

C and Si both have same lattice structure; having 4 bonding electrons in each. However, C is insulator where as Si is intrinsic semiconductor. This is because

Show answer and solution

Answer: (c)

C ( $1s^2 2s^2 2p^2$ ) has its four bonding electrons in the 2nd orbit; Si ( $\ldots 3s^2 3p^2$ ) has them in the 3rd orbit.
Electrons in the 2nd orbit are closer to the nucleus and more tightly bound, so the band gap of C (about $5.4\text{ eV}$ ) is much larger than that of Si ( $1.1\text{ eV}$ ).
Hence C is an insulator and Si a semiconductor.
So the answer is (c).

Report a mistake

Energy Bands in Solids question from NEET 2012 (AIPMT, Prelims)

More questions on Energy Bands in Solids