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Democritus, c470-370 BC, GREECE
Democritus was a Greek philosopher/scientist. He made a significant contribution with his atomic theory of the universe: all things originate from a vortex of tiny, indivisible particles, which he called atoms. Atomism - the theory that suggested that the natural world consisted of two essential (and opposite) invisible bodies – atoms and void (nothingness).
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Sir Isaac Newton, 1643-1727, ENGLAND
Newton proposed a mechanical universe with small solid masses constantly in motion. He suggested that atoms were held together by forces/attractions. wikipedia note: all images are from Wikipedia. (Thanks) -
John Dalton, 1766-1844, ENGLAND
Dalton explained that chemical combination is based on the interaction of atoms of definite and characteristic WEIGHT. Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass. When atoms combine to form a particular compound, they always combine in the same ratios by weight. -
Dmitri Mendeleev, 1834-1907, RUSSIA
He is credited as being the creator of the first version of the periodic table of elements. Using the table, he predicted the properties of elements yet to be discovered. He attempted to classify the elements according to their chemical properties and he noticed patterns that led him to his Periodic Table. -
George Johnston Stoney, 1826-1911, IRELAND
Stoney introduced the ELECTRON as "the fundamental unit quantity of electricity." One of the most important works he made was the conception and calculation of the magnitude of the "atom of electricity."
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Sir Joseph John Thomson, 1856-1940, ENGLAND
Thomson discovered the electron. (He won a Nobel Prize for Physics in 1906 for discovering the electron and for his work on the conduction of electricity in gases.) He proposed that electricity was made of discrete negative particles he called electrons. -
Max Planck, 1858-1947, GERMANY
Max Planck was considered to be the founder of Quantum Physics, which is a branch of physics providing a mathematical description of much of the wave-like behavior and interactions of energy and matter. In the mid-1920s, developments in quantum mechanics quickly led to its becoming the standard formulation for atomic physics. -
Hantaro Nagaoka, 1865-1950, JAPAN
Nagaoka developed an early, incorrect "planetary model" of the atom. The model was based around an analogy to the explanation of the stability of the Saturn rings (the rings are stable because the planet they orbit is very, very massive). Two predictions made from the model were a very massive nucleus (a very massive planet) and electrons revolving around the nucleus, bound by electrostatic forces (the rings revolving around Saturn, bound by gravitational forces).
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Robert A. Millikan, 1868-1953, AMERICA
Oil drop experiment determined the charge (e=1.602 x 10 -19 coulomb) and the mass (m = 9.11 x 10 -28 gram) of an electron. -
Ernest Rutherford, 1871-1937, BRITAIN/NEW ZEALAND
Rutherford is known as the "Father of Nuclear Physics." He won a Nobel Prize for Chemistry and this is because he discovered the concept of radioactive half-life, His most well-known achievement was when he maintained that atoms have their positive charge concentrated in a very small nucleus, and thus made the Rutherford model of the atom, through his discovery and interpretation of Rutherford scattering in his gold foil experiment. -
Henry G-J Moseley, 1887-1915, ENGLAND
Moseley's contribution to atomic physics was the justification from physical laws of the previous chemical concept of the atomic number. Before Moseley's Law, atomic numbers were thought to have just put the elements in a neat sort of order. However, since Moseley's Law, our understanding of the atom and its atomic number has improved; we now know that atomic numbers have a strong physical basis.
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Niels Bohr, 1885-1962, DENMARK
The Bohr model of the atom, the theory that electrons travel in discrete orbits around the atom's nucleus and the shell model of the atom, where the chemical properties of an element are determined by the electrons in the outermost orbit were achieved by Bohr, who received a Nobel Prize for physics in 1922.
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Sir James Chadwick, 1891-1974, ENGLAND
Chadwick won a Nobel Prize for his discovery of a neutral atomic particle of the nucleus which had similar mass to the proton. This was the NEUTRON. Chadwick’s discovery made it possible to create elements heavier than uranium in the laboratory.
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