History of the Atom Notes zDalton pg Zumdahl zThomson pg 91 Figure 4.3 Zumdahl pg 97 & 98 LeMay zMillikan pg 98 LeMay zRutherford pg LeMay Figure 3-16 pg 91 –93 Zumdahl zMoseley pg 104 LeMay zChadwick pg 94 Zumdahl zBohr pg Zumdahl Figure pg 284 –287 Zumdahl

History of the Atom White Board Presentations Democritus (example) zGreek philosopher, around 400 BCE zProblem with previous model: no system or explanation, just “magic” zModel: z“atomos” compose the world- tiny, indivisible particles that retain the chemical identity of the element

History of the Atom White Board Presentations John Dalton zEnglish schoolteacher, zProblem w/ previous model: No logical/scientific structure or rules zAtomic Theory Of Matter: y5 postulates (next slide) zModel:

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 zEnglish physicist, zProblem w/ previous model: no subatomic particles zExperimental Evidence: cathode ray tube experiment where particles smaller than atoms are shown to have negative charge (electrons) with a small mass to charge ratio zModel: Plum Pudding Model:

History of the Atom White Board Presentations Robert Millikan zAmerican physicist, zProblem w/ previous model: no known amount of charge of an electron zExperimental evidence: oil drop experiment where (-) charged oil drops pass between (+) plates and rate of fall is measured. All were multiples of 1.60 x C (one e - ). zHe also calculated the mass of an e - based on the charge and the known mass:charge ratio. zModel: (looks the same as Thomson’s)

History of the Atom White Board Presentations Ernest Rutherford zScientist from New Zealand, zProblem w/ previous model: does not account for  particles bouncing back zExperimental 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. zModel: Nuclear atom

History of the Atom White Board Presentations Henry Moseley zEnglish scientist, (Rutherford’s student) zProblem w/ previous model: does not account for elemental differences zExperimental 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) zModel: (looks the same as Rutherford’s)

History of the Atom White Board Presentations Sir James Chadwick zEnglish physicist, zProblem w/ previous model: mass of protons did not account for mass of nucleus and a nucleus of all protons (+) would repel and fall apart zExperimental evidence: He bombarded metals (beryllium) with  particles, causing a radiation that was both neutral and a mass similar to a proton zModel: (looks the same as Rutherford's, but with neutrons in the nucleus as well)

History of the Atom White Board Presentations Niels Bohr zDanish physicist, zProblem w/ previous model: did not account for specific energy levels of e - seen in the light spectrum analysis zExperimental evidence: The energy spectrum of hydrogen shows discrete “quanta” of energy involved in e - configurations zModel: (Bohr model)

Info on Experimentation: zThomson's Experiment: zCathode Ray tube- zMillikan's Experiment: s/pqp_errata/cd_errata_fixes/section4_5.html s/pqp_errata/cd_errata_fixes/section4_5.html zOil Drop- zHere’s what the drops would actually look like… don’t watch the whole thing. It’s hypnotic- zRuthorford's Experiment: zGold Foil-