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MATERIAL STRUCTURE AND INTERATOMIC

BONDING

T
he existence of atoms has been proposed since the time of early Indian and Greek
philosophers (400BC) who were of the vies that atoms are the fundamental building
blocks of matter. The word ‘atom’ has been derived from the Greek word ‘a-tomio’ which
means ‘uncut-able’ or ‘non-divisible’. These ideas were mere speculations and there was no

way to test them experimentally and remained dormant for a very long time and were
revived again by scientists in the nineteenth century. In 1808 Dalton atomic theory had been
proposed by John Dalton, a British school teacher. The theory was able to explain the law of
conservation of mass, law of constant composition and law of multiple proportion very
successfully. However, it failed to explain the results of many experiments, for example, it

was known that substances like glass or ebonite when rubbed with silk or fur get electrically
charged. In this topic, we start with the result obtained by scientists towards the end of
nineteenth and beginning of twentieth century. These established that atoms are made of sub-
atomic particles, i.e., electrons, protons and neutrons.

Atom

Basically, atom is the smallest unit of matter in one unit. One atom consists primarily
of three basic subatomic particles which are, protons, neutrons and electrons. Protons and

neutrons are in the center of the atom, making up the nucleus. Electron surround the nucleus.
Figure 2.1: Illustrates nucleus, electron and orbits surrounding nucleus. Protons have a
positive charge. Electrons have a negative charge. The charge on the proton and electron are
exactly same size but opposite charge. Neutrons have no charge. Since opposite charges

attract, protons and electrons attract each other.

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