Notes Key   History Of The Atom Teacher
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Notes Key History Of The Atom Teacher

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Notes Key   History Of The Atom Teacher Notes Key History Of The Atom Teacher Presentation Transcript

  • History of the Atom
  • Democritus
    • Proposed that all matter is composed of tiny, indivisible particles called “ atomos”
    • Today, we define an atom as the smallest part of an element that retains the chemical identity of that element
  • Dalton’s Atomic Theory (1807)
    • 1) Elements are made of tiny particles called atoms.
    • 2) All atoms of a given element are identical.
    • 3) The atoms of a given element are different from those of any other element.
  • Dalton’s Atomic Theory (cont.)
    • Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative numbers and types of atoms.
  • Dalton’s Atomic Theory (cont.)
    • 5) Atoms are indivisible in chemical processes. That is, chemical reactions do not create or destroy atoms, they simply change the way the atoms are grouped together.
  • Some of Dalton’s Symbols for the Elements
  • Sir William Crookes (1879)
    • Invented the cathode ray tube and investigated electrical charges in gases.
  • Figure 3.7 : Schematic of a cathode ray tube
  • John Joseph (JJ) Thomson (1903)
    • Discovered the negatively charged particles ( 0 -1 e)
    • Proposed the “plum pudding model”
    • Postulated the positive particles
  • Ernest Rutherford (1909)
    • Discovered the positively charged dense central portion of the atom using his “gold foil experiment”
    • 1 1 p
  • Figure 3.5 : Rutherford’s experiment
  • Figure 3.6: Results of foil experiment if Plum Pudding model had been correct
  • Figure 3.6 : Actual Results.
  • Figure 3.9 : A nuclear atom viewed in cross section
  • Niels Bohr (1913)
    • Electrons are located in specific energy levels
    • Electrons move in a definite orbit around the nucleus
  • James Chadwick (1932)
    • Discovered the third subatomic particle (neutron)
    • Neutron has no charge and a mass of ~1 amu
    • 1 0 n
  • Figure 3.10 : Two isotopes of sodium. Mass number ( A ) = protons + neutrons Atomic Number ( Z ) = protons A Z X
  • An Ion of Sodium