Explain how materials can be classified into three groups on the basis of atomic structure.

An atom has a positively charged nucleus surrounded through a group of negatively charged electrons. This nucleus is at the centre of the atom and electrons are established in definite states, energy-levels and orbits. The electrons in the outermost orbit of an atom are termed as valence electrons. This is these electrons which are responsible for finding the physical, electrical and chemical properties of the material.

The materials are classified on the basis of atomic structure:

1) When the number of valence electrons of an atom is less than 4 that is half of maximum permissible 8 electrons, the material is a conductor or metal. Illustration Cu, Al and Mg have 1, 2 and 3 valence electrons correspondingly.

 2) When the number of valence electrons of an atom is more than 4, the material is an insulator. Illustration, Se and Bromine consist of 5, 6 and 7 valence electrons correspondingly.

3) When the number of valence electrons of an atom is 4 that are exactly half of maximum permissible 8 electrons, therefore the material is a semiconductor. Illustration Carbon, Silicon and Germanium consist of 4 valence electrons each.