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απόψεις
για το άτομο στην διάρκεια του χρόνου
Greek era
Democritus
"by convention bitter, by convention sweet, but in reality atoms and void"
1704
Isaac
Newton
Proposed a mechanical universe with small solid masses in motion.
1803
John Dalton
Proposed an "atomic theory" with spherical solid atoms based upon measurable
properties of mass.
1832
Michael Faraday
Studied the effect of electricity on solutions, coined term "electrolysis" as a
splitting of molecules with electricity, developed laws of electrolysis.
Faraday
himself was
not a proponent
of atomism.
1859 J.
Plucker
Built one of the first gas discharge tubes ("cathode ray tube").
1869
Dmitri Mendeleeff
Arranged elements into 7 groups with similar properties. He discovered that the
properties of elements "were periodic functions of
the their atomic weights".
This
became known
as the
Periodic Law.
1873
James Clerk Maxwell
Proposed electric and magnetic fields filled the void.
1874
G.J. Stoney
Proposed that electricity was made of discrete negative particles he called "electrons".
(Link
to info
on electrons)
1879
Sir William
Crookes
Discovered cathode rays had the following properties: travel in straight lines
from the cathode; cause glass to fluoresce; impart a negative charge to objects
they strike; are deflected by electric fields and magnets to suggest a negative
charge; cause pinwheels in their path to spin indicating they have mass.
1886
E. Goldstein
Used a CRT to study "canal rays" which had electrical and magnetic properties
opposite of an electron.
1895
Wilhelm Roentgen
Using a CRT he observed that nearby chemicals glowed. Further experiments found
very penetrating rays coming from the CRT that were not deflected by a magnetic
field.
He
named them "X-rays".
1896
Henri Becquerel
While studying the effect of x-rays on photographic film, he discovered some
chemicals spontaneously decompose and give off very
pentrating rays.
1897
J.J. Thomson
Used a
CRT
to experimentally determine the charge to mass ratio
(e/m)
of an electron =1.759 x 108 coulombs/gram.
1897
J.J. Thomson
Studied "canal rays" and found they were associated with the proton H+
.
1898
Rutherford
Studied radiations emitted from uranium and thorium and named them alpha
and beta.
1898
Marie Sklodowska
Curie
Studied uranium and thorium and called their spontaneous decay process
"radioactivity". She and her husband Pierre also discovered the radioactive
elements polonium and radium.
1900
Soddy
Observed spontaneous disintegration of radioactive elements into variants he
called "isotopes" or totally new elements, discovered "half-life", made initial
calculations on energy released during decay.
1900
Max Planck
used the idea of quanta (discrete units of energy) to
explain hot glowing matter.
1903
Nagaoka
Postulated a "Saturnian" model of the atom with flat
rings of electrons revolving around a positively charged particle.
1904
Abegg
Discovered that inert gases had a stable electron configuration which lead to
there chemical inactivity.
1906
Hans Geiger
Developed an electrical device to "click" when hit with alpha particles.
1909
R.A. Millikan
Oil drop experiment determined the charge (e=1.602 x 10-19 coulomb)
and the mass (m = 9.11 x 10-28 gram) of an electron.
1911
Ernest Rutherford
Using alpha particles as atomic bullets, probed the atoms in a piece of thin
(0.00006 cm)
gold foil.
He established that the nucleus was: very dense,very
small and positively charged. He also assumed that the electrons were located
outside the nucleus.
1914
H.G.J. Moseley
Using x-ray tubes, determined the charges on the nuclei of most atoms. He
wrote"The atomic number of an element is equal to
the number of protons in the nucleus". This work was used to reorganize the
periodic table based upon atomic number instead of atomic mass.
1919 Aston
Discovered the existence of isotopes through the use of a mass spectrograph.
1922
Niels Bohr
Developed an explanation of atomic structure that
underlies regularities of the periodic table of elements. His atomic model had
atoms built up of sucessive orbital shells of
electrons.
1923
de Broglie
Discovered that electrons had a dual nature-similar to both particles and waves.
Particle/wave
duality. Supported
Einstein.
1927
Heisenberg
Described atoms by means of formula connected to
the frequencies of spectral lines. Proposed Principle of
Indeterminancy - you can not know both the position and velocity of a
particle.
1929
Cockcroft / Walton
Built an early linear accelerator and bombarded lithium with protons to produce
alpha particles
1930
Schrodinger
Viewed electrons as continuous clouds and introduced "wave mechanics" as a
mathematical model of the atom.
1930
Paul Dirac
Proposed anti-particles.
Anderson
discovered the anti-electron (positron) in 1932 and Segre/Chamberlain
detected the anti-proton in 1955.
1932 James
Chadwick
Using alpha particles discovered a neutral atomic particle with a mass close to
a proton.
Thus
was discovered
the neutron.
1938
Lise Meitner, Hahn,
Strassman
Conducted experiments verifying that heavy elements
capture neutrons and form unstable products which undergo fission. This process
ejects more neutrons continuing the fission chain reaction.
1941
- 51
Glenn Seaborg
Synthesized 6 transuranium elements and suggested a
change in the layout of the periodic table.
1942
Enrico Fermi
Conducted the first controlled chain reaction releasing energy from the atoms
nucleus.
1950's -
New findings/particles
Follow this link to current theories a
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