Question

Pure silicon and germanium behave as:
(A) conductors
(B)semiconductors
(C) insulators
(D) piezoelectric crystals

Answer 1

The periodic table has elements which have their properties ranging between the metals and non-metals and thus, show transitional behaviour. The temperature and dopant also play an important role in enhancing the properties of the element.

Complete step by step solution:
The pure silicon and germanium atom belong to the group 14 of the periodic table, having four valence electrons forming covalent bonds in the diamond-like crystal lattice, thus making it a poor conductor.
But they are not completely insulators like the carbon atom in the same group, because they have an extra shell, making the outermost electrons loosely bound to the nucleus and so less energy is needed to exchange the electrons.
Thus, the pure silicon and germanium atom have a transitional behaviour between the conductors and the insulator. Thus, making them a semiconductor and are also known as a metalloid.

Therefore, the pure silicon and germanium are option (B)- semiconductors.

Additional information:
The silicon and germanium have equal numbers of holes and electrons within it, so even in the absence of any extra element (dopant) added to it, it still shows its conducting properties. Thus, making it an intrinsic semiconductor.
The process of doping, that is, the addition of the extra elements in the semiconductor makes it n-type or p-type depending on the carrier (electrons or holes) produced, on adding a Group 15 and Group 13 elements respectively.

Note: The conductivity of the semiconductor is low at the room temperature. But it increases with the increase in temperature, unlike the general metallic conductors, where the atomic vibration increases with temperature and hinders the movement of electrons. This is because, with an increase in temperature, the electrons in semiconductors break free from the bonds easily and conduct electricity.