Notes

Atomic Theory

Epicurus and the Atom: The first man to expound an atomic theory was Democritus, in about 400 BC. Epicurus (341 to 270 BC) was a student of his theory that all things are composed of minute, invisible, indestructible particles of pure matter which move about eternally in infinite emptiness. Although the technology to research this theory was not available, Democritus and Epicurus were surprisingly accurate.

In the 17th and early 18th Centuries, the theory was sidetracked a little by The Calorists, who believed that heat was a subtle fluid called caloric. But people such as Robert Boyle in the 19th Century, an English schoolmaster and chemist, and a little later, John Dalton, updated and refined Democritus’ work and published Modern Atomic Theory. Dalton’s work inspired the man who perhaps made the most important contribution to the theory: J.J. Thompson, who discovered the electron in 1897. Shortly thereafter Thompson published his Plum Pudding model, which suggested that electrons and protons were randomly placed throughout the atom. This theory was incorrect, but it inspired the discovery of the nucleus, by Ernest Rutherford. These ideas were refined by Niels Bohr and later by Rutherford again and finally, James Chadwick’s discovery, in 1932, of the neutron, a nuclear particle with very nearly the same mass as the proton but no electric charge, gave us the model we know of today: a nucleus with orbiting electrons, neutrons and protons.

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