Atoms Development of the Atomic Theory by hcj

VIEWS: 20 PAGES: 10

									     Atoms:
Development of the
  Atomic Theory


                     1
                  Democritus
   460 BC - Greek philosopher proposes
    the existence of the atom
   His theory:
      all atoms are small hard particles
     made of a single material

     always moving

     form different materials by joining




                                            2
               John Dalton
   1803 - British chemist; elements
    combined in specific proportions to form
    compounds.
   His theory:
     allsubstances are made of atoms that
      cannot be created, divided, or destroyed
     atoms join with other atoms to make new
      substances
     atoms of the same element are exactly
      alike,
                                                 3
              J.J. Thomson
   1897 - English chemist and physicist
    discovered 1st subatomic particles
   His theory:
     negatively charged particles called
      electrons
     positively charged particles
     created a model to describe the atom as a
      sphere filled with positive matter with
      negative particles mixed in
     plum pudding model
                                              4
          Ernest Rutherford
   1912 - New Zealand physicist
    discovered the nucleus
   His theory:
     Proton-small,  dense, positively charged
      particle present in nucleus
     electrons travel around the nucleus, but
      their exact places cannot be described



                                                 5
                  Niels Bohr

   1913 - Danish physicist discovered
    energy levels
   His theory:
     electrons  travel around the nucleus in
      definite paths and fixed distances
     electrons can jump from one level to a
      path in another level
     http://www.youtube.com/watch?v=wCCz2
      0JOXXk                                  6
           Erwin Shrodinger
   1924 - Austrian physicist developed
    the electron cloud model
   His theory:
      electrons exact path cannot be predicted
     regions, referred to as the electron cloud,
      are areas where electrons can likely be
      found.
     http://www.youtube.com/watch?v=2qzCT
      PnieJE
                                                    7
           James Chadwick

   1932 - English physicist discovered
    neutrons
   His theory:
     neutrons  have no electrical charge
     neutrons have a mass nearly equal to the
      mass of a proton
     unit of measurement for subatomic
      particles is the atomic mass unit (amu)

                                                 8
    Modern Theory of the Atom
   The type of atom is determined by the
    number of protons it has.
   The number of protons in an atom is equal to
    the atomic number
   The sum of the number of protons and
    neutrons in a particular atom is called the
    atomic mass
   Valence electrons are the outermost
    electrons and are where bonding takes
    place
                                                  9
    Modern Theory of the Atom
   Atoms are composed of three main
    subatomic particles: the electron, the
    proton, and the neutron.
   Most of the mass of the atom is concentrated
    in the nucleus of the atom.
   The protons and neutrons are located within
    the nucleus while the electrons exist outside
    of the nucleus.
   In stable atoms, the number of protons is
    equal to the number of electrons.
                                                10

								
To top