Solved: PHYSICS Question for NEET

NEET PHYSICSMedium

C and Si both have the same lattice structure, having 4 bonding electrons in each. However, C is an insulator whereas Si is an intrinsic semiconductor. This is because:

in case of C, the valence band is not completely filled at absolute zero temperature.

in case of C, the conduction band is partly filled even at absolute zero temperature.

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 orbit.

the four bonding electrons in the case of C lie in the third orbit, whereas for Si they lie in the fourth orbit.

Step-by-Step Solution

Electronic Configuration: Carbon (atomic number 6) has the electronic configuration $1s^2 2s^2 2p^2$ , meaning its 4 valence (bonding) electrons are in the second principal quantum shell ( $n=2$ ). Silicon (atomic number 14) has the configuration $1s^2 2s^2 2p^6 3s^2 3p^2$ , so its 4 valence electrons are in the third shell ( $n=3$ ).
Band Gap: Because the valence electrons in carbon are in the $n=2$ orbit, they are much closer to the nucleus and more tightly bound than the $n=3$ electrons in silicon.
Conclusion: This strong binding in carbon results in a very large energy gap (band gap $\approx 5.4\text{ eV}$ ) between the valence band and the conduction band, making diamond (carbon) an insulator. In contrast, the electrons in silicon are farther from the nucleus, resulting in a smaller band gap ( $\approx 1.1\text{ eV}$ ), which allows it to act as an intrinsic semiconductor at room temperature.

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