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### Theory:

Atom:
The substance is a form of matter which have a constant chemical composition and specific properties.
Various types of atoms

Element:
Element is a pure chemical substance made up of atoms with the same numbers of protons, electrons and neutrons.
Structure of atom
• In the world, all substances are made up of certain unique elements.
• So far, $$118$$ elements are identified; in nature, $$92$$ elements and others are prepared by laboratories.
• Element is made up of identical, tiny particles called atoms.
• The word 'atom' is obtained from the Greek word 'atomos'. Atomos means indivisible (cannot be split or divided).
• Greek philosophers Democritus and Tamil poet Avvaiyar mentioned atoms in their writings.
• John Dolton first introduced the atomic theory, followed by J.J.Thomson and Rutherford.