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Democritus introduced the idea of the atom as the basic building block matter. -
was the first complete attempt to describe all matter in terms of atoms and their properties. -
the electron and then went on to propose a model for the structure of the atom. -
the discovery that atoms contain a positively charged nucleus much smaller than the actual atom. -
in which he proposed that energy levels of electrons are discrete and that the electrons revolve in stable orbits around the atomic nucleus but can jump from one energy level (or orbit) to another. -
made a fundamental discovery in the domain of nuclear science: he proved the existence of neutrons – elementary particles devoid of any electrical charge.