Atom

By a001751
  • 2000 BCE

    Alchemy

    Lab procedures were developed, but alchemists did not
    perform controlled experiments like true scientists.
  • 400 BCE

    Democritus

    Proposed that matter was composed of tiny indivisible particles

  • John Dalton

    Elements are made of
    tiny particles called
    atoms.

  • John Dalton

    Conservation of atoms—
    rearrangement in RXN
    (Lavoisier previously stated
    this in terms of the Law of
    Conservation of Matter)

  • John Dalton

    Different atoms form
    compounds in constant
    ratios.

  • John Dalton

    British Schoolteacher
    – based his theory on others’
    experimental data

  • John Dalton

    Billiard Ball Model
    – atom is a
    uniform,
    solid sphere

  • Michael Faraday

    The structure of
    atoms is
    somehow related
    to electricity

  • Henri Becquerel

    Three types:
    – alpha () - positive
    – beta () - negative
    – gamma () - neutral

  • Henri Becquerel

    Discovered radioactivity
    – spontaneous emission of
    radiation from the nucleus

  • J. J. Thomson

    Discovered atoms have
    negative particles
    (electrons) using a
    cathode ray tube.

  • J. J. Thomson

    Discovered electron’s
    charge to mass ratio:
    1.76 x 108
    C/g

  • Frederick Soddy

    came up with the term “isotope” to explain the unintentional breakdown of radioactive elements.

  • J. J. Thomson

    Cathode Ray Tube
    Experiments
    – beam of negative particles

  • J. J. Thomson

    Plum-pudding Model

  • J. J. Thomson

    Discovered Electrons
    – negative particles within
    the atom

  • J. J. Thomson

    Plum-pudding Model
    – positive sphere
    (pudding) with
    negative electrons
    (plums) dispersed
    throughout

  • John Dalton

    Atoms of one element are
    identical while atoms of
    different elements are
    different

  • Hantaro Nagaoka

    proposed an atomic model called the Saturnian Model to describe the structure of an atom.

  • Richard Abegg

    found that inert gases have a “stable electron configuration.

  • Hans Geiger

    invented a device that could detect alpha particles.

  • Robert Millikan

    Measured the
    charge of an
    electron using oil
    droplets

  • Robert Millikan

    Electron’s charge:
    1.60 x 10-19 C

  • Robert Millikan

    Electron’s mass:
    9.11 x 10-28 g

  • Ernest Ruthefor

    Gold Foil Experiment

  • Ernest Ruthefor

    Discovered the nucleus
    – dense, positive charge in
    the center of the atom

  • Ernest Ruthefor

    Nuclear Model
    – dense, positive nucleus surrounded
    by negative electrons

  • Niels Bohr

    Bright-Line Spectrum
    – tried to explain presence
    of specific colors in
    hydrogen’s spectrum

  • Niels Bohr

    Energy Levels
    – electrons can only exist in
    specific energy states

  • Niels Bohr

    Planetary Model
    – electrons move in circular
    orbits within specific
    energy levels

  • H.G.J. Moseley

    discovered that the number of protons in an element determines its atomic number

  • Francis William Aston

    used a mass spectrograph to identify 212 isotopes.

  • Erwin Schrödinger

    An electron does not travel in an exact orbit

  • Erwin Schrödinger

    We can predict where it will probably be

  • Erwin Schrödinger

    We cannot say for certain where it is, but only where it ought to be

  • Erwin Schrödinger

    The type of probability orbit is dependent on the energy level described by Bohr

  • Niels Bohr

    proposed an atomic structure theory that stated the outer orbit of an atom could hold more electrons than the inner orbit.

  • Louis de Broglie

    roposed that electrons have a wave/particle duality.

  • Erwin Schrödinger

    Quantum mechanics
    – electrons can only exist in
    specified energy states

  • Erwin Schrödinger

    Electron cloud model
    – orbital: region around the
    nucleus where e- are likely
    to be found

  • Erwin Schrödinger

    Electron Cloud Model (orbital)
    • dots represent probability of finding an enot actual electrons

  • Cockcroft / Walton

    created the first nuclear reaction, producing alpha particles

  • Paul Dirac

    proposed the existence of anti-particles

  • James Chadwick

    discovered neutrons, particles whose mass was close to that of a proton.

  • James Chadwick

    Discovered neutrons
    – neutral particles in the
    nucleus of an atom

  • James Chadwick

    Joliot-Curie
    Experiments
    – based his theory on their
    experimental evidence

  • James Chadwick

    Neutron Model
    • revision of Rutherford’s Nuclear Model

  • Lise Meitner, Hahn, Strassman

    discovered nuclear fission.

  • Glenn Seaborg

    discovered eight transuranium elements.

  • Enrico Fermi

    created the first man-made nuclear reactor.