atomic theory

  • 400 BCE


    Democritus, a philosopher in ancient Greece,
    began the search for a description of matter.
    He questioned whether matter could be
    divided into smaller and smaller pieces
    forever until eventually the smallest possible
    piece would be obtained. He believed that
    the smallest possible piece of matter was
    indivisible. He named the smallest piece of
    matter “atomos,” meaning “not to be cut.”
  • 300 BCE


    In ancient Greece, the popular
    philosopher Aristotle declared
    that all matter was made of only
    four elements: fire, air, water
    and earth. He also believed that
    matter had just four properties:
    hot, cold, dry and wet.
  • dalton

    In the early 1800s, the English Chemist John
    Dalton performed a number of experiments
    that eventually led to the acceptance of the
    idea of atoms. He formulated the first atomic
    theory since the “death of chemistry” that
    occurred during the prior 2000 years.
  • thomson

    In 1897, the English scientist named J.J.
    Thomson provided the first hint that an
    atom is made of even smaller particles.
    He discovered the presence of a negative
    particle in the atom – the electron.
  • einstien

    Einstein also in 1905 mathematically proved the existence of atoms, and thus helped revolutionize all the sciences through the use of statistics and probability. Atomic theory says that any liquid is made up of molecules (invisible in 1905).
  • rutherford

    In 1908, the English physicist Ernest
    Rutherford performed an experiment using
    positively charged particles fired at gold foil.
    Through his experiment, he proved that
    atoms are not a “pudding” filled with a
    positively charged material. He theorized
    that atoms have a small, dense, positively
    charged center, which he called the
  • bohr

    In 1913, the Danish scientist Niels Bohr
    proposed an improvement. He built on the
    concept that the mass of an atom is
    contained mostly in the nucleus.
  • shrodinger

    Based on de Broglie's idea that particles could exhibit wavelike behavior, Austrian physicist Erwin Schrödinger theorized that the behavior of electrons within atoms could be explained by treating them mathematically as matter waves.
  • heinsberg

    Werner Heisenberg contributed to atomic theory through formulating quantum mechanics in terms of matrices and in discovering the uncertainty principle, which states that a particle's position and momentum cannot both be known exactly.
  • Modern Cloud Theory

    According to today’s atomic
    theory, electrons do not orbit
    the nucleus in neat planet-like
    orbits but move at high speeds
    in an electron cloud around the