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400 BCE
Democritus
Democritus discovered the atomic theory through philosophical reasoning and "thought experiments". He proposed that all matter was composed of tiny, indivisible particles, which he called atomos. -
John Dalton
He proposed that matter is composed of indivisible and indestructible atoms, each element having unique atoms, and that atoms combine in simple whole-number ratios to form compounds. -
JJ Thompson
He discovered the electron and the proposal of the "plum pudding" model of the atom in 1897, which suggested that atoms are composed of negatively charged electrons within in a sphere of positive charge. -
Ernest Rutherford
He discovered the atomic nucleus through the gold foil experiment, which led to the development of the nuclear model of the atom. -
Niels Bohr
He proposed the Bohr model which suggests that electrons move around the nucleus in fixed, stable orbits, with specific energy levels. This idea helps explain how atoms absorb and emit light. -
James Chadwick
He discovered the neutron, a neutral subatomic particle with a mass like a proton. It sits in the nucleus alongside protons, completing our understanding of the atom's structure.