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1
THEORY OF ATOM
he difference between the elementary and the comDosite substances He proved that composite substances are formed by the combination of one or more primary elements An element is not a composite substance He also proved that there are Lfferences in the atomic weights of different elements, and that, if elements are made to combine in the same proportion, the result will always be the same Thus the door for researches for the discovery of primary clements was opened and with the beginning of the uneteenth century, their number came up to thirty.
1 Hydrogen. 2 Helium
3 Lithium
4. Verilnum
In the course of those studies, as the hydrogen atom was found to be the smallest of all, it was at irst considered that it alone was the elementary paracle But this theory could not last long When iydrogen atom was more accurately weighed, it was clear that it cannot be the primary ingredient of ll other elements The accepted definition of an element then was "A substance which is not the he result of any mixture and which is composed of elementary 'atoms' of a definite character" By now he number of elements gradually increased from the original five and has reached to 92 These 92 elements
ure as follows
73
5 Boron.
6 Carbon.
7 Nitrogen 8. Oxygen
