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The History of the Atom

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Title: The History of the Atom


1
The History of the Atom
2
Democritus(c.460-c.370 BCE)
  • Democritus was a philosopher in ancient Greece.
  • He thought that all matter was made of tiny
    particles that could not be divided.
  • The Greek word atomos means indivisible.

3
John Dalton(1766-1844)
  • Dalton was an English scientist.
  • He developed modern atomic theory.
  • His model of the atom is sometimes called the
    billiard-ball model.

4
Daltons Billiard-Ball Model
  • All matter is made of tiny particles called
    atoms.
  • Atoms of the same element are identical.
  • Atoms can combine to form compounds.
  • Chemical reactions change the grouping of atoms,
    but not the atoms themselves.

5
Sir J. J. Thomson(1856-1940)
  • Thomson was a British physicist.
  • He did experiments on cathode rays and discovered
    the electron.
  • In 1906, he was awarded a Nobel prize for his
    discovery.
  • His model of the atom is called the plum-pudding
    model.

6
Thomsons Plum-Pudding Model
  • Dalton realised that negatively charged electrons
    could come from an atom.
  • He proposed the plum-pudding model of the atom,
    suggesting that atoms consist of
    negatively-charged electrons in a sea of
    positive charge.

7
Ernest Rutherford(1871-1937)
  • Rutherford was a chemist from Nelson, New
    Zealand.
  • Based on the results of his gold-foil experiment,
    he proposed that most of the mass of an atom is
    concentrated in a central nucleus.
  • He won the Nobel Prize in Chemistry in 1908 for
    his work.

8
Rutherfords Gold-Foil Experiment
  • In his famous gold-foil experiment, Rutherford
    fired alpha particles at a thin sheet of gold
    foil.
  • He found that some particles were deflected
    through large angles, and some even bounced back.

9
Rutherfords Nuclear Model
  • Rutherford concluded that
  • most of the mass in an atom must be in a very
    small, positively-charged nucleus in the centre
    of the atom
  • electrons spin around this central nucleus
  • there was a basic unit of positive charge in the
    nucleus, called the proton.

10
  • Niels Bohr (1885-1962) realised that the
    electrons could only occupy fixed orbits around
    the nucleus.
  • Louis de Broglie (1892-1987) proposed that
    electrons can be regarded as waves, resulting in
    an electron cloud around the nucleus.
  • Sir James Chadwick (1891-1974) discovered the
    neutron, a nuclear particle with similar mass to
    a proton but no electrical charge.

11
References
  • Atom Image http//www.turbosquid.com/FullPreview/
    Index.cfm/ID/197928
  • Democritus http//smccd.net/accounts/goth/MainPag
    es/Chron/Democritus.jpeg
  • Dalton http//en.wikipedia.org/wiki/John_Dalton
  • Thomson http//en.wikipedia.org/wiki/J_J_Thomson
  • Plum-Pudding Atom https//reich-chemistry.wikispa
    ces.com/file/view/348px-Plum_pudding_atom_svg.png
  • Ernest Rutherford http//en.wikipedia.org/wiki/Ea
    rnest_Rutherford http//nobelprize.org/nobel_prize
    s/chemistry/laureates/1908/rutherford-bio.html
  • Gold-Foil Experiment http//wps.prenhall.com/wps/
    media/objects/602/616516/Media_Assets/Chapter02/Te
    xt_Images/FG02_05.JPG
  • Nuclear Atom http//upload.wikimedia.org/wikipedi
    a/commons/thumb/e/e1/Stylised_Lithium_Atom.svg/180
    px-Stylised_Lithium_Atom.svg.png
  • Electron Cloud http//www.csmate.colostate.edu/cl
    tw/cohortpages/viney_old1/atom.jpg
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