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460 BCE
Democritus (460 B.C.)
-Greek philosopher, Democritus, develop the idea of atoms. He asked this question: If you break a piece of matter in half, and then break it in half again, how many breaks will you have to make before you can break it no further? Democritus thought that it ended at some point, a smallest possible bit of matter. He called these basic matter particles, atoms.
-Abdera, Greece
(http://www.nobeliefs.com/atom.htm) -
Period: 405 BCE to
Atomic Theory
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John Dalton (1803)
-Dalton, considered the father of modern atomic theory, made a logbook entry that day titled, "Observations on the Ultimate Particles of Bodies and their Combinations." It was the first use of symbols to represent the elements of modern chemistry.
- Eaglesfield, England
(https://archive.wired.com/science/discoveries/news/2008/09/dayintech_0903) -
J.J. Thomson (1897)
-Thomson showed that cathode rays were composed of unknown negatively charged particles, must have bodies much smaller than atoms and a very large value for their charge-to-mass ratio.He is credited with the discovery/identification of the electron; and discovery of the subatomic particle.Also credited with finding the first evidence for isotopes of a stable element, as part of his studies into the composition of canal rays. (Cheetham Hill, England)
(https://en.wikipedia.org/wiki/J._J._Thomson) -
Robert Millikan (1909) ;Morrison, Illinois, U.S.
In 1909 Millikan began a series of experiments to determine the electric charge carried by a single electron. He began by measuring the course of charged water droplets in an electric field. The results suggested that the charge on the droplets is a multiple of the elementary electric charge, but the experiment was not accurate enough. He obtained more precise results in 1910 with his oil-drop experiment in which he replaced water with oil.
(https://en.wikipedia.org/wiki/Robert_Andrews_Millikan) -
Ernest Rutherford (1911); New Zealand
Although he could not prove that it was positive or negative,he theorized that atoms have their charge in a very small nucleus,and created the Rutherford model of the atom, through his discovery and interpretation of Rutherford scattering by the gold foil experiment of Hans Geiger and Ernest Marsden. He conducted research that led to the first "splitting" of the atom in 1917 in a nuclear reaction, in which he also discovered the proton.(https://en.wikipedia.org/wiki/Ernest_Rutherford) -
Niels Bohr (1922)
-Bohr developed the Bohr model of the atom, in which he proposed that energy levels of electrons are discrete and that the electrons revolve in stable orbits around the atomic nucleus but can jump from one energy level (or orbit) to another.
-(Copenhagen, Denmark)
(https://en.wikipedia.org/wiki/Niels_Bohr) -
Louis de Broglie (1924)
-In 1923, de Broglie stated, a wave confined within boundaries imposed by the nuclear charge would be restricted in shape and, thus, in motion, because any wave shape that did not fit within the atomic boundaries would interfere with itself and be canceled out. .In this thesis(1924), de Broglie developed his revolutionary theory of electron waves, which he had published earlier in scientific journals.
-(Dieppe, France)
(https://www.britannica.com/biography/Louis-de-Broglie) -
Erwin Schrödinger (1926)
-Erwin Schrödinger developed an “Electron Cloud Model” in 1926. It consisted of a dense nucleus surrounded by a cloud of electrons at various levels in orbitals.
-(Vienna, Austria)
(https://www.msnucleus.org/membership/html/jh/physical/atomictheory/lesson1/atomic1g.html) -
James Chadwick (1932)
-In 1932, Chadwick made a discovery in the domain of nuclear science: he proved the existence of neutrons - elementary particles devoid of any electrical charge.
-(Cheshire,England)(http://www.nobelprize.org/nobel_prizes/physics/laureates/1935/chadwick-bio.html)
