THE ATOM TIME LINEAlchemists - 500 BC-1720
Ancient art practice especially in the Middle Ages, devoted
chiefly to discovering a substance that would transmute the more
common metals into gold or silver, and to finding a means of
indefinitely prolonging human life. Although its purposes and
techniques were often illusory, alchemy was in many ways the
predecessor of modern science, especially chemistry.
Democritus - 442 BC
Postulated the theory of atoms and void; the universe is made
up of empty space and a nearly
Democritus - 442 BCPostulated the theory of atoms and void; the universe is madeup of empty space and a nearly infinite number or invisibleparticles differing in arrangement, form, and position. Hestated that all all matter is composed of indivisible atoms.
John Dalton - 1803English chemist who proposed the Atomic Theory which
stated that all matter was composed of small indivisible
particles called atoms. These atoms possess unique
characteristics and weight for different elembets.
He also stated that three types of atoms exist: simple
(elements), compound (simple molecules), and complex
J.J. Thomson - 1898First to measure the electron. Developed the
plum-pudding model of the atom. Describes the atom as a
slightly positive sphere with small electrons inside.
Ernest Rutherford - 1909-1911Inferred a small, dense, positively-charged nucleus as theresult of the alpha particle scattering gold foil experiment.
Neils Bohr - 1913A Danish physicist who stated that electrons could only
orbit the nucleus in succesively larger orbits around the
nucleus. The outer orbits could hold more electrons. The
electrons in the outermost shell determine the properties of
the atom. He also inferred that when an electron moves from
an outer orbit to an inner orbit it emits a quantum of energy,
a photon, in the form of light.
Erwin Schroedinger - 1926Developed wave mechanics which describe the behavior
of quantum systems for bosons.
Chadwick - 1931Discovered the neutron.