* Ancient Greeks: Philosophers like Democritus and Leucippus proposed the idea of atoms, the smallest indivisible particles. However, this was purely philosophical and lacked experimental evidence.
* John Dalton (1803): He provided the first scientific foundation for the atomic theory, based on experimental observations of chemical reactions. He proposed that elements are composed of identical atoms that cannot be broken down further.
* J.J. Thomson (1897): Discovered the electron, proving that atoms are not indivisible and have internal structure.
* Ernest Rutherford (1911): His gold foil experiment revealed the nucleus at the center of the atom, containing protons.
* Niels Bohr (1913): Developed a model of the atom with electrons orbiting the nucleus in specific energy levels.
* Quantum mechanics (20th century): Modern physics refined our understanding of atoms and their particles. We now know atoms are composed of protons, neutrons, and electrons, and these can be further broken down into even smaller particles called quarks.
So, while Dalton is often credited with the "modern" atomic theory, the particle theory of matter is a product of many scientists building upon each other's work over a long period.
