- Alchemists - 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 infinite number or invisible
particles differing in arrangement, form, and position. He
stated that all all matter is composed of indivisible atoms.
- Aristotle - 384-322 BC
- Developed methods for the gathering of scientific fact.
His work provided the basis for scientific work more than a
- Lavoisier - 1777
- A French chemist who proved the conservation of matter
and explained the mysteries of fire.
- Coulomb - 1780's
- Formed Coulomb's Law: the force one timy charged object
exerts on a second one is proportional to the amount of
charge on one times the amount of charge on the others
and inversely proportional to the square of the distance
- John Dalton - 1803
- English 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
- Crookes - 1870's
- Developed the Crookes tube and in it produced cathode
rays for the first time. He also invented the radiometer and
- W.K. Roentgen - 1895
- Discovered x-rays
- Becquerel - 1896
- A French physicist who found that rays coming from a
uranium ore affected a photographic plate like X-rays did.
The rays were not from an external source and were more
powerful than those from a sample of pure uranium. His
experiment led to the discovery of natural radioactivity.
- The Curies - 1898
- Studied and identified radioactive elements.
- J.J. Thomson - 1898
- First to measure the electron. Developed the
plum-pudding model of the atom. Describes the atom as a
slightly positive sphere with small electrons inside.
- Max Planck - 1900
- Stated that radiation is quantized.
- Albert Einstein - 1905
- Proposed the quantum of light in which he states that light
behaves like a particle but also has a wave nature, giving it
a dual nature. Stated the equivalence of energy and mass
through the theory of special relativity.
- Robert Millikan - 1908-1917
- Discovered the charge of an electron with his oil drop
- Ernest Rutherford - 1909-1911
- Inferred a small, dense, positively-charged nucleus as the
result of the alpha particle scattering gold foil experiment.
- Neils Bohr - 1913
- A 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.
- Geiger - 1925
- Demonstrated that energy and mass are conserved in
- Erwin Schroedinger - 1926
- Developed wave mechanics which describe the behavior
of quantum systems for bosons.
- Chadwick - 1931
- Discovered the neutron.
- Otto Hahn - 1938
- Found that when Uranium is bombarded by neutrons it
produces smaller nuclei roughly half the size of the original
- Lise Meitner - 1938
- Realized that Hahn was splitting the Uranium nucleus,
something never done before.
- Glen Seaborg - 1951
- Succeeded in making man-made elements.
- Murray Gell-Mann and George Zweig - 1964
- Suggested the idea of quarks called up, down, or strange,
composed of mesons and baryons, with spin 0.5 and
electric charges of 2/3, -1/3, and -1/3 respectively.