ATOMIC STRUCTURE:-

• An element is defined as a substance which cannot be decomposed into other substances. The smallest particle of an element which takes part in chemical reaction is known as atom.
• All matter is composed of atoms which are infinitesimally small.
• All atoms are made of electrons, protons and neutrons. Most solid materials are classed, from the stand point of electrical conductivity, as conductors, semiconductors or insulators. To be conductor, the substance must contain some mobile electrons. on that can move freely between atoms. These free electrons come only from the valence (outer) orbit of the atom. Conductivity depends on the number of electrons in the valence orbit.

“The energy level of an electron increases as its distance from the nucleus increases. Thus an electron in the second orbit possesses more energy than electron in the first orbit, electrons in the third orbit have higher energy than in the second orbit and so on. It follows ;therefore, that electrons in the last orbit will possess very high energy.

These high energy electrons are less bound to the nucleus and hence they are more mobile. It is the mobility of last orbit electrons that they acquire the property of combining with other atoms. Further due to this combining power of last orbit electrons of an atom they are called valence electrons”

• Atoms with fewer than four valence electrons are good conductors
• Atoms with more than four valence electrons are poor conductors
• Atoms with four valence electrons are semi-conductors.