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Jun 1, 1000
Democrtius (Greece)
Developed the theory that the universe consists of empty space and an almost infinite number of particles that differed in form, position and arrangement- he introduced the concept of the atom.
http://particleadventure.org/other/history/earlyt.html -
Issac Newton (England)
Proposed a universe that was made of small particles in motion stating that "matter is formed of solid, massy, impenetrable particles"
www.cartage.org.lb/.../atomicphysics/atomicstructure/atomictimeline/atomictimeline.htm -
John Dalton (England)
Wikipedia- Atomic TheoryDalton developed a model based on extensive observations of pure substances. He said that matter was made of tiny indivisible particles which he called atoms. His atoms could join together to form molecules in a regular predictable way.
Dalton also devised a system of chemical symbols and, having measured the relative weights of atoms, arranged them into a table. He then theorised that compounds were made up of molecules, and that molecules are composed of atoms in definite proportions. -
G.J Stoney (Ireland)
Stoney made a significant contribution to the theory of gases. He estimated the number of molecules in a cubic millimetre of gas, at room temperature and pressure. His conception and calculation of the magnitude of the "atom of electricity" resulted in his proposition of the term electron to describe the unit of electrical charge en.wikipedia.org/wiki/George_Johnstone_Stoney http://www.cartage.org.lb/en/themes/sciences/physics/atomicphysics/atomicstructure/atomictimeline/atomictimeline.htm -
J.J. Thomson (Britain)
Thomson discovered tiny negatively charged particles which he called electrons. He discovered them when he subjected gases in glass tubes to high voltages. Thomson was also able to determine the charge to mass ratio (e/m) of the electron =1.759 x 108 coulombs/gram. http://www.cartage.org.lb/en/themes/sciences/physics/atomicphysics/atomicstructure/atomictimeline/atomictimeline.htm nobelprize.org/nobel_prizes/physics/.../thomson-bio.html -
Planck (Germany)
Planck is considered to be the inventor of the quantum theory. He was able to deduce the relationship between the energy and the frequency of radiation based on the idea that the energy by a resonator could only take on discrete values or quanta. Through this he discovered a new constant which he called Planck’s constant and later described his own set of units of measurement based on fundamental physical constants. http://nobelprize.org/nobel_prizes/physics/laureates/1918/planck-bio.html -
Nagaoka (Japan)
Nagaoka developed an early
(though slightly incorrect) model of the atom. The model was based around an analogy to the explanation of the stability of the Saturn rings. The model made two predictions:
• The nucleus is big
• the electrons that revolve around the nucleus are bound by electrostatic forces http://www.cartage.org.lb/en/themes/sciences/physics/atomicphysics/atomicstructure/atomictimeline/atomictimeline.htm http://en.wikipedia.org/wiki/Hantaro_Nagaoka -
Milikan (USA)
Milikan accurately determined the charge carried by an electron using the “falling-drop method” and proved that this quantity was the same for all electrons. http://nobelprize.org/nobel_prizes/physics/laureates/1923/millikan-bio.html -
Ernest Rutherford (New Zealand)
Rutherford was able to probe atoms in a piece of thin gold foil using alpha particles. He established that the nucleus was very dense and small and that it had a positive charge. He also theorised the existence of neutrons which could somehow explain the repelling effect of the positive charges of the protons. This theory was proved by his associate James Chadwick. http://en.wikipedia.org/wiki/Ernest_Rutherford http://www.cartage.org.lb/en/themes/sciences/physics/atomicphysics/atomicstructure/ -
H.G.J Mosely (England)
Using X-ray crystallography i Moseley discovered a systematic mathematical relationship between the wavelengths of the X-rays produced and the atomic numbers of the metals that were used as the targets in X-ray tubes. http://www.barringtonhighschool.org/Chemistry_Web/Chem%20history/Mosely/moseley.htm http://en.wikipedia.org/wiki/Henry_Moseley -
Bohr (Denmark)
Bohr developed an atomic model where the atoms where built up of successive orbital shells of electrons. He expanded a past theory made by Ernest Rutherford by proposing that electrons travel only is certain successively larger orbits. He suggested that the outer orbits could hold more electrons than the inner ones and that the outer orbits determine the atom’s chemical properties. http://www2.lucidcafe.com/lucidcafe/library/95oct/nbohr.html -
James Chadwick (England)
Using alpha particles Chadwick made a fundamental discovery in the domain of nuclear science in 1932. He discovered an elementary particle devoid of any electrical charge- the neutron. http://www.cartage.org.lb/en/themes/sciences/physics/atomicphysics
/atomicstructure/atomictimeline/atomictimeline.htm http://nobelprize.org/nobel_prizes/physics/laureates/1935/chadwick-bio.html
