Who Discovered the Atom? (History of Atomic Theory)

The ancient Greek philosopher Democritus first proposed the concept of the atom around 400 BC.

He reasoned: if you keep cutting a piece of matter in half, again and again, you must eventually reach the smallest possible piece that cannot be cut any further. He called this particle the 'Atomos' (Greek for 'indivisible' or 'uncuttable').

This was brilliant philosophical reasoning — but not yet proven by experiment.

John Dalton is credited as the Father of Modern Atomic Theory. In 1808, he published 'A New System of Chemical Philosophy' with key proposals:

1. All matter is made of tiny, indivisible particles called atoms
2. Atoms of the same element are identical
3. Atoms combine in fixed ratios to form compounds

Dalton's model: atom as a solid, indivisible sphere (like a billiard ball).

• J.J. Thomson (1897): Discovered the electron — proving the atom IS divisible! Model: 'Plum Pudding' (electrons embedded in positive matter)
• Ernest Rutherford (1911): Gold foil experiment proved atoms have a tiny, dense nucleus with electrons orbiting it
• Niels Bohr (1913): Electrons orbit in fixed energy levels (shells)
• Modern Quantum Model: Electrons exist in probability clouds, not fixed orbits