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Atoms are the building blocks of all matter. Over 2,500 years ago, Democritus proposed this idea, but without proof, it was dismissed. Around 1800, English scientist John Dalton revived it.
Dalton's experiments revealed that elements consist of indivisible atoms, which combine in fixed ratios to form compounds. For example, water always forms with two hydrogen atoms and one oxygen atom, maintaining a 2:1 ratio—never more or less.
To visualize this, Dalton introduced the Billiard Ball Model, imagining atoms as solid wooden spheres. Using wooden balls with holes, he demonstrated how atoms combine to form compounds.
He also proposed that atoms cannot be created, destroyed, or divided. Imagine splitting water; it always produces two hydrogen and one oxygen atom, which remain unchanged.
Additionally, hydrogen atoms are identical to each other, as are oxygen atoms, but hydrogen and oxygen differ in properties. This means atoms of the same element share identical properties, while atoms of different elements have distinct properties.
Later, Thomson refined Dalton’s idea by discovering the first subatomic particle—the electron.
