"The rich diversity of chemical behaviour of different elements can be traced to the difference in the internal structure of atoms of these elements."
The existence of atoms has been proposed since the time of early Indian and Greek philosophers (400B.C.) who were of the view that atoms are the fundamental building blocks of matter.
According to them, the continued subdivisions of matter would ultimately yield atoms which derived from the Greek word 'a-tomio' which means 'uncut- able' or non-division'. These earlier ideas were mere speculations and there was no way to test them experimental.
These ideas remained dormant for a very long time and revived again by scientists in the nineteenth century.
The atomic theory of matter was first proposed on a firm scientific basis by John Dalton, a British school teacher in 1808.
His theory, called Dalton,s atomic theory, regarded the atom as the ultimate particle of matter.
In this article we start with the experimental observations made by scientists towards the end of nineteenth and beginning of twentieth century.
These atomic particles, i.e, electrons, protons and neutrons- a concept very different from that of Dalton
The major problem before the scientists at that time were:
- to account for the stability of atoms after the discovery of sub-atomic particles,
- to compare the behaviour of one element from other in terms of both physical and chemical properties,
- to explain the formation of different kinds of molecules by the combination of different atoms and,
- to under the origin and nature of the Characteristics of eleromagnetic characteristics absorbed or absorbed or emitted by atoms.
SUB- ATOMIC PARTICLES
Dalton's atomic theory was able to explain the law of conservation of mass, low of constant composition and low of multiple properties very successfully. However, it failled to explain the results of many experiments for example, it was known that substances like glass or ebonite when rubbed with silk or fur generate electricity. Many different kinds of sub- atomic particles were discovered in the twentieth century.
However I this section we will about only two particles, namely electron and proton.
