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ATOMS Structure & Properties

ATOMS Structure & Properties. Atomic structure Periodic table Problem of atomic spectra. Democritus 4 th Century B.C. Atoms as elementary blocks of matter Thomson discovers electron (1900) -> Plum Pudding Model of atom ( a guess )

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ATOMS Structure & Properties

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  1. ATOMS Structure & Properties • Atomic structure • Periodic table • Problem of atomic spectra

  2. Democritus 4th Century B.C. • Atoms as elementary blocks • of matter • Thomson discovers electron (1900) • -> Plum Pudding Model of atom • (a guess) • Plums (electrons) • = negative electric charge centers • Pudding = positive electric charge • Rutherford (1911) • Atoms as small nucleus of positive charge, • surrounded by orbiting electrons

  3. Rutherford’s experiment Plum Pudding Model Nuclear Model Note: Nucleus later found to be composed of protons (positive charge particles) and neutrons (electrically neutral particles)

  4. Properties of atoms • # electrons = # protons (electrical neutrality) • # electrons determines chemical properties Hydrogen –>1 electron Z=1 Helium –> 2 electrons Z=2 Lithium –> 3 electrons Z=3 …… Uranium –> 92 electrons Z=92 92 natural `elements’ Explains the Periodic Table of Chemistry

  5. Electron always accelerating • Accelerating charge radiates light (Maxwell) • Electron would lose its energy, • spiralling into nucleus • -> atoms unstable Trouble with Rutherford’s Model! Also, radiated light from an atom would have all wavelengths (colors) But real atoms emit/absorb light of a few discrete wavelengths E.g. Balmer lines of Hydrogen

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