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In 1803 John Dalton pictures atoms as tiny, indestructible particles, with no internal structure.
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In 1897, J.J. Thomson, a British scientist, discovers the electron. This later leads to his "plum-pudding" model. He pictures electrons embedded in a sphere of positive electrical charges.
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Hantaro Nagaoka, a Japanese physicist, suggests that an atom has a central nucleus. Electrons move in orbits like the rings around Saturn.
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In Niels Bohr's model, the electron moves in a circular orbit at fixed distances from the nucleus.
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French physicist Louis de Broglie proposes that moving particles like electrons have some properties of waves. Within a few years, experimental evidence supports the idea
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In 1926, Erwin Schrodinger develops the mathematical equations to describe the motion of electrons in the atom. His work leads to the electron cloud model.
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James Chadwick, an English physicist, confirms the existence of neutrons, which have no charge. Atomic nuclei contain neutrons and positively charged protons.