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1803 JOHN DALTON PICTURES ATOMS AS TINY, INDESTRUCTIBLE PARTICLES, WITH NO INTERNAL STRUCTURE.
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1897 J.J. Thomson, a British scientist, discovers the electron. The later leads to his “plum-pudding” model. He pictures electrons embedded in a sphere of positive electrical charge.
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1904 Hantaro Nagaoka, a Japanese physicist, suggests that an atom has a central nucleus. Electrons move in orbits like the ring around Saturn.
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1911 New Zealand physicist Ernest Rutherford finds that an atom has a small, dense positively charged nucleus. Electrons move around the nucleus.
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1913 In Niels Bohr’s model, the electrons move in a circular orbit at fixed distance from the nucleus.
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1923 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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1926 Erwin Schrodinger develops mathematical equations to describe the motion of electrons in atoms. His work leads to the electron cloud model.
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1932 James Chadwick an English physicist, confirms the existence of neutrons, which have no charge. Atomic nuclei contain neutrons and positively charged protons.
