Question

At absolute zero, Silicon acts as
A. non-metal
B. metal
C. insulator
D. semiconductor

Answer 1

Hint:All the elements in the periodic table can be broadly classified into two types- metals and non-metals. There exist a certain class of elements which falls in group 14 and they are called semiconductors. Under ordinary conditions of temperature semiconductors are insulators. The electrons, the mobile electrons, are generally present in the conduction band and for any element to conduct electricity these electrons from the valence band must jump into the conduction band.

Complete answer:
We know that silicon is a semiconductor. At absolute zero the band gap for a semiconductor becomes in order of 3 eV. A substance is able to conduct electricity if the electrons in the valence band can jump to the conduction band. Since this is not possible for the semiconductors like Si at zero kelvin as the free electrons that are responsible to conduct electricity in semiconductors do not possess the required kinetic energy leaving the conduction band empty.

Therefore Silicon (Si) behaves as an insulator at absolute zero.Due to the insufficient energy in the electrons of silicon and absolute zero it cannot overcome the band gap of 3 eV to jump from the valence band to the conduction band and thus act as an insulator.

So, the correct option is C.

Note: An element behaves as a conductor if its electron from the valence band can jump to the conduction band crossing the band gap. The insufficient energy of the electron of silicon to cross this band gap makes an insulator at absolute zero. Conductors are the substances that allow electricity to pass through it whereas insulators do not allow the flow of electricity. Semiconductors conduct electricity partially due to the free electrons present in it whereas they act as an insulator at absolute zero.