Here's a breakdown of key figures and their contributions:
* Ancient Greeks (Democritus, Leucippus): They proposed the idea of indivisible particles called "atomos" (meaning "uncuttable"). However, this was purely philosophical and lacked experimental evidence.
* John Dalton (1803): His atomic theory, based on experimental evidence, was a major turning point. He proposed that elements are composed of atoms, that atoms of a given element are identical, and that atoms combine in whole-number ratios to form compounds.
* J.J. Thomson (1897): His discovery of the electron proved that atoms were not indivisible. He proposed the "plum pudding model," where electrons were embedded in a positively charged sphere.
* Ernest Rutherford (1911): He conducted the gold foil experiment, which showed that most of the atom's mass and positive charge are concentrated in a tiny nucleus. This led to the nuclear model.
* Niels Bohr (1913): He combined Rutherford's model with quantum theory, proposing that electrons orbit the nucleus in specific energy levels.
* Erwin Schrödinger (1926): He developed the quantum mechanical model, which describes electrons as waves rather than particles and uses probabilities to predict their location.
So, while Dalton is often credited with the first "modern" atomic theory, it was a collective effort of many scientists over centuries to refine and develop our understanding of atomic structure.
