History of Atomic Theory

Democritus, a Greek philosopher, first proposed that matter is made of fundamental, indivisible particles called "atomos." However, this was a philosophical concept without scientific evidence.

John Dalton provided the first empirical evidence for atoms. He proposed that compounds consist of atoms in whole number ratios and that chemical reactions rearrange these atoms. This explained observations like the constant mass ratio in water and the way elements combine to form different compounds.

J.J. Thomson discovered the electron, demonstrating that atoms are not indivisible and contain smaller, negatively charged particles. His cathode ray experiment led to the "plum pudding model," where electrons were embedded in a positively charged sphere.

Ernest Rutherford's gold foil experiment showed that atoms have a small, dense, positively charged nucleus and that most of the atom is empty space. This drastically revised the atomic model, with electrons orbiting a central nucleus.

The progression from Democritus to Rutherford shows how our understanding of atomic structure has evolved, laying the foundation for modern chemistry, even though further revisions to the atomic model would come later.