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History of the Atom Notes Dalton Thomson pg 88-89 Zumdahl pg 91 Figure 4.3 Zumdahl pg 97 & 98 LeMay Millikan pg 98 LeMay Rutherford pg 100-101 LeMay Figure 3-16 pg 91 –93 Zumdahl Moseley pg 104 LeMay Chadwick pg 94 Zumdahl Bohr pg 287-288 Zumdahl Figure 10-17 pg 284 –287 Zumdahl History of the Atom White Board Presentations Democritus (example) Greek philosopher, around 400 BCE Problem with previous model: no system or explanation, just “magic” Model: “atomos” compose the world- tiny, indivisible particles that retain the chemical identity of the element History of the Atom White Board Presentations John Dalton English schoolteacher, 1766-1844 Problem w/ previous model: No logical/scientific structure or rules Atomic Theory Of Matter: 5 postulates (next slide) Model: Atomic Theory of Matter 1. Each element is composed of atoms 2. All atoms of a given element are identical 3. All atoms of different elements are different (#2 and #3 often combined) 4. Atoms are neither created nor destroyed 5. Atoms combine to form compounds and a given compound has the same relative numbers and kinds of atoms History of the Atom White Board Presentations JJ Thomson English physicist, 1856-1940 Problem w/ previous model: no subatomic particles Experimental Evidence: cathode ray tube experiment where particles smaller than atoms are shown to have negative charge (electrons) with a small mass to charge ratio Model: Plum Pudding Model: History of the Atom White Board Presentations Robert Millikan American physicist, 1869-1953 Problem w/ previous model: no known amount of charge of an electron Experimental evidence: oil drop experiment where (-) charged oil drops pass between (+) plates and rate of fall is measured. All were multiples of 1.60 x 10-19C (one e-). He also calculated the mass of an e- based on the charge and the known mass:charge ratio. Model: (looks the same as Thomson’s) History of the Atom White Board Presentations Ernest Rutherford Scientist from New Zealand, 1871-1937 Problem w/ previous model: does not account for particles bouncing back Experimental evidence: gold foil experiment where he shot (+) charged particles at very thin gold foil and saw evidence for a very small, dense, positively charged core to the atom. Model: Nuclear atom History of the Atom White Board Presentations Henry Moseley English scientist, 1887-1915 (Rutherford’s student) Problem w/ previous model: does not account for elemental differences Experimental evidence: X-Ray diffraction patterns of metals showed that each element has a unique positive charge in the nucleus that determines the atoms identity (atomic number) Model: (looks the same as Rutherford’s) History of the Atom White Board Presentations Sir James Chadwick English physicist, 1891-1974 Problem w/ previous model: mass of protons did not account for mass of nucleus and a nucleus of all protons (+) would repel and fall apart Experimental evidence: He bombarded metals (beryllium) with particles, causing a radiation that was both neutral and a mass similar to a proton Model: (looks the same as Rutherford's, but with neutrons in the nucleus as well) History of the Atom White Board Presentations Niels Bohr Danish physicist, 1885-1962 Problem w/ previous model: did not account for specific energy levels of e- seen in the light spectrum analysis Experimental evidence: The energy spectrum of hydrogen shows discrete “quanta” of energy involved in e- configurations Model: (Bohr model)
