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History of the Atom. Democritus of Abdera. Democritus: 460-370 BCE Greek mathematician and philosopher Co-author (with Leucippus) of the idea that all matter made of small parts atoma Proposed that the behaviour of substances was due to the type of atom. Aristotle.
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Democritus of Abdera • Democritus: 460-370 BCE • Greek mathematician and philosopher • Co-author (with Leucippus) of the idea that all matter made of small parts • atoma • Proposed that the behaviour of substances was due to the type of atom
Aristotle • Greek Philosopher: 384-322 BCE • Not an ‘atomist’ • Proposed all matter made up of 5 elements: • Fire • Air • Water • Earth • Aether
Robert Boyle • Robert Boyle: 1627-1691 • Performed experiments with controls and published detailed results • 1661: Published claiming that Aristotle's ideas were incorrect • Some 'elements' (like mercury) did not contain the Greek elements (earth, air, fire, water)
John Dalton • Dalton: 1766-1844 • Law of Multiple Proportions (1803): elements combine in mass ratios of small whole numbers. • Small whole numbers reflect the atoms involved, therefore there are atoms • Atomic theory contains 4 hypotheses
Dalton’s Atomic Theory • Elements are made of small particles called atoms. (Dalton viewed atoms as small spheres of differing characteristics.) • All atoms of an element are identical. All atoms of one element are different from atoms of other elements. • Compounds are made of atoms of more than one element. The ratio of the elements is a simple fraction. • A chemical reaction involves separation, combination or rearrangement of atoms.
Joseph John Thomson • 1856-1940 • Used a cathode ray tube to determine the presence of electrons 1897 • Suggested the plum pudding model of the atom and the existence of isotopes • Won the Nobel Prize in Physics in 1906
Robert A. Millikan • 1858-1953 • Used the 'falling drop method' to determine the charge of the electron (-1.6022 x 10-19 C) and mass of electron as 9.10 x 10-28 g • Investigated photoelectric effect and spectroscopy of elements • Won the Nobel Prize in Physics in 1923
Marie Curie • 1867-1934 • Worked with husband Pierre to study radioactivity • Isolated elements polonium and radium • Shared Nobel Prize in Physics 1903, won Nobel Prize in Chemistry 1911 for work with radioactive elements.
Ernest Rutherford • 1871-1937 • Investigated release and measurement of different forms of radiation from elements (α, β, γ) • Gold foil experiment with Geiger and Marsden led to new model of an atom • Model:ruther14.swf • Nobel Prize in Chemistry 1908
Model of the atom in the early 1900s • Nucleus: has positive charge, very small, but very dense • Proton: same charge as electron, but opposite. Mass=1.67262 x 10-24 g • Vast empty space around nucleus contains electrons
Where are the electrons? • Niels Bohr: 1885-1962 • Collaborated with Rutherford • Used emission spectra to propose Bohr model of atom 1913 • Electrons found in specific ‘orbits’ around nucleus • Most of atom is empty space • Nobel Prize Physics 1922
James Chadwick • 1891-1974 • Discovered the neutron and worked on fission of atoms • Discovery of neutron (mass = 1.67493 x 10-24 g) explained the mass problem of many atoms • Nobel Prize in Physics 1935
Current Model • Based on the previous work, as well as Einstein, Heisenberg, Born, Schrödinger and others • Nucleus contains p+ and no • Made of smaller particles called quarks • uud, ddu (baryons) • Electron cloud • e- are in areas of probability, predicted by wave equations • leptons