Events
-Alchemists
500BC- develop the theory—that all metals are composed of mercury and sulphur and that it is possible to change base metals into gold.-Democritus
400 B.C. atomic theory posited that all matter is made up small indestructible units he called atoms.-Aristotle
300BC He also believed that everything was a combination of the four elements: earth, fire, water, air. His theory was that a mass of incomprehensible size was everywhere; he called this 'hyle'. There was no separate 'particles' for each material, it was all one.-Joseph Priestly
1733-1804 (discovered oxygen) isolated several gases and showed how
they could be produced from other subsances. These early chemists
began to scientifically discuss the substances they were isolating.
Discussions lead to new experiments, which guided the way to further
discoveries.J.J. Thomson
1897, determined the charge to mass ratio of electrons.-Niels Bohr
1922 proposed an atomic
structure theory that stated
the outer orbit of an atom could
hold more electrons than the inner orbit.-Robert Brown
1827, the British botanist
Robert Brown observed
that dust particles inside
pollen grains floating in
water constantly jiggled
about for no apparent reason.James Chadwick
1932 James was most famous for his discovery of the neutron in an atom.Ernest Rutherford
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