Atomic model

Tracing the history of Atomic models

  • 400

    Democritus- Greece c.400BCE

    Democritus- Greece c.400BCE
    • believed atoms can combine as they have different shapes
    • believed everything is either made up of space or atoms
    • thought that atoms determine properties, e.g. edges of atoms
      lead to the differences in taste and colour of substances
    • thesis not based on scientific evidence, but attempted to explain the concept of an atom and how atoms form the physical world
  • Period: 400 to

    Tracing the history of Atomic models

    Please note that the year 400 is c. 400 BCE,
  • Newton- England

    Newton- England
    • provided the basis for later atomic theory research: allow
      many later theories to be built upon his Laws of Motion, theory of gravity, etc.
    • Suggested a mechanical universe with small solid masses in motion
    • Law of Gravity states that all matter are pulled together by gravity: allow other scientists to use this in regards to atomic theory- that opposite forces will keep atoms at a certain distance from each other
  • Dalton- England

    Dalton- England
    • Experiment: to see how soluble different gases are in water, and found that each dissolve differently- concluded that the gases have atoms of different masses
    • Dalton's Atomic Thoery:
    • All matter are made of atoms.
    • Atoms of the same element are identical.
    • Atoms of different elements have different properties &
    • Atoms make up compound in simple ratios.
    • Atoms are neither created nor destroyed.
    • Dalton summarised all the major principles of atomic theory
  • G. J. Stoney- Ireland

    G. J. Stoney- Ireland
    • found that there must be some fundamental unit of electricity related to atoms
    • most important work: calculated the magnitude of electrons
    • proposed that the 'electron' is one of the 3 fundamental units; the others are gravity and velocity of light
    • laid doundation for the discovery of 'electron' by J. J. Thomson
  • J. J. Thomson- England

    J. J. Thomson- England
    • through cathode-ray experiment, found negatively charged particles which he called 'corpuscles'.
    • found these 'corpuscles' present in all elements
    • 'raisin pudding model' his atomic model showed negaticely charged particles distributed evenly among positively charged particles in the atom
    • improved our understanding of sub-atomic particles and raised quesitons about the structure of matter
  • Planck- Germany

    Planck- Germany
    • originator of quantum theory
    • explained that energy is released in chunks called 'quanta' and not in a continuous stream
    • his discovery of quantum theory transformed our understanding of the world of atoms and sub-atomic structures
  • Nagaoka- Japan

    Nagaoka- Japan
    • developed a 'Saturnian model' of atom portraying a positively charged particle in the middle surrounded by negatively charged particles like the ring of Saturn
    • gave us an general idea of how electrons are arranged in an atom
  • Millikan- America (born in NZ)

    Millikan- America (born in NZ)
    • through his well-known oil-drop experiment, he found the charge of a single electron
    • this discovery allows the calculation of the mass of electorn and the mass of positively charged atoms
  • E. Rutherford- America

    E. Rutherford- America
    • through his experiment related to radioactivity, he found that half of the atoms of a radioactive substance would disintegrate, leaving 'half-life' of the matter behind
    • through examination of alpha particles, concluded that atoms contain a small nucleus which takes most of the weight, while the rest is empty space where electrons orbit the nucleus
    • first person to separate an atomby ejecting the proton
    • contribute to our understanding of the structure of an atom and the proton
  • H. G. J. Mosely- England

    H. G. J. Mosely- England
    • noted that the lines produced by the X-ray spectra of more than 30 metallic elements move according to atomic weight
    • Mosely's Law: founf a relationship between the frequencies of the radiaiton & the atomic no.
    • noted that thje atomic no. = positive charge of atom nucleus
    • Mosely predicted the properties of several elements in the periodic table & over the years, we were able to slot them in
    • he found a vital ilink between the physical make-up and the chemical properties of an element
  • Bohr- England (Born in Denmark)

    Bohr- England (Born in Denmark)
    • in Bohr's atomic model, electons only exist in fixed orbits
    • suggested that electrons move up or down an orbit when absorbing ro releasing energy
    • showed that hte characteristics of an element can be predicted by the electrical configuration of tis atom
    • contributed to our understanding of the behaviour of atoms and electrons
  • James Chadwick- England

    James Chadwick- England
    • discovered neutrons
    • discovery of neutrons made up for the missing 50% of the mass of the atom
    • found that these neutrons with the same weight as protons could force protons out of substances containing hydrogen
    • completed our understanding of sub-atomic structure of atom