Download Timeline of Atomic Theory--pdf

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The Atomic Theory of Matter
c.460 BCE - c.370 BCE
The Atomic Theory, a cornerstone of modern science, was proposed by
an early Greek thinker, Democritus.
Atomic Weights
1808
John Dalton, an English chemist, stated that each atom of any given
element is identical to every other atom of that element, including weight.
The Periodic Table
1871
Dmitry Mendeleyev, a Russian chemist, revealed the basic importance of
atomic weights and of nuclear structure. His work also showed the
significance of structure in comprehending the behavior and properties of
matter.
Cathode Rays
1887
Sir William Crookes, an English chemist and physicist, pioneered work on
cathode rays.
X-Rays
1895
While studying cathode rays, German physicist Wilhelm Röentgen noticed
some glowing barium platinocyanide across the room from his experiment.
This led to the discovery of X-rays. His work helped found a major new
medical technique and played an important role in revealing the secrets of
the atom and its nucleus.
Radioactivity
1896
French physicist Antoine Henri Becquerel discovered radioactivity.
The Electron
1897
English physicist Sir J. J. Thomson explained the nature of the electron.
Radium
1902
Marie Curie and her husband, Pierre, discovered the radioactive elements
polonium and radium. Their work confirmed the existence of radioactivity.
E=mc2
1905
For more than two centuries, scientists had unquestionably believed that
the basic quantities of measurement -- mass, length, and time -- were
absolute and unvarying. The German-born physicist Albert Einstein
showed that in fact they depended very much on the relative motion
between the observer and whatever was being observed.
The Nuclear Model
1909
Sir Ernest Rutherford's great contribution to modern science was to show
what happens to an element during radioactive decay. This enabled him to
construct the first nuclear model of the atom, a cornerstone of present-day
physics.
The Electron Orbit
1913
Niels Bohr modified Rutherford's model of the atom to incorporate the
ideas of quantum physics. This required a new mechanism for the way
electrons emitted energy.
Transformation of Atoms
1919
Rutherford's work, which he published in 1919, demonstrated that atoms
could be transformed from those of one element into those of another by
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means of artificial tampering with the nucleus. Far more important, his
experiment demonstrated that the nucleus of an atom could be breached.
The Neutron
1932
British physicist Sir James Chadwick is best known for discovering the
neutron, one of the fundamental particles making up the nucleus of atoms.
The neutron differed from all other particles then known by having no
electrical charge.
The Atom is Split 1932
Sir John Douglas Cockroft and his colleague, Ernest T. S. Walton,
developed the Cockroft-Walton particle accelerator. Using it in 1932, they
managed to boost the speed of protons to the point where the voltage was
high enough to energize each atom of lithium, their target metal, to form
two atoms of helium. This was the first example of man-made nuclear
transformation.
Uranium and Fission
1938
German scientists Otto Hahn and Fritz Strassmann discovered that a tiny
portion of the uranium atom's mass could be converted into an estimated
200 million electron volts of potentially usable energy. This process was to
be called fission.