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100
Democritus
Greek philosopher ((400 BC)) who adopted the Atomic Theory from his mentor/ developed the concept of the 'atom', He believed that everything in the universe was made up of atoms, which were microscopic and indestructible. -
Period: 100 to
time
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Dmitri Mendeleev
Russian chemist who published a periodic table in 1869 and also arranged the elements known at the time in order of relative atomic mass. -
J Lothar Meyer
German chemist who was one of the pioneers in developing the first periodic table of chemical elements. -
Photoelectric Effect
First observed by Heinrich Hertz where he saw that many metals produce electrons when light shines upon them. -
JJ Thomson
English physicist who discovered and identified the electron in 1897 (also the 1st subatomic particle). -
Cathode Ray Tube
A vacuum tube that contains at least one electron gun and a phosphorescent screen that is used to view images. Discovered by JJ Thomson. -
Max Planck
German theoretical physicist who originated quantum theory, which contributed significantly to the understanding of atomic and subatomic pressures, winning him the Nobel Prize in Physics in 1918. -
Plum Pudding Model
A model that shows the atom composed of electrons surrounded by positive charge which balance the electrons' negative charges.(similar to negatively charged "plums" in positively charged "pudding"). Discovered by JJ Thompson -
Orbitals
A mathematical function which describes wave-like behavior of either one electron or a pair of electrons in an atom. This can be used to calculate the chances of discovering any electron of an atom around the atom's nucleus. This is the idea that electrons might revolve around a nucleus that is compact with definite angular momentum. This was discovered by Niels Bohr but published by Hantaro Nagaoka in 1904. -
Ernest Marsden
Discovered the deflection paths of alpha particles, with Hans Geiger, in 1909. -
Robert Millikan
Between the years of 1909, Millikan worked on an oil-drop experiment in which he measured the charge on a single electron. -
Oil-drop Experiment
An atomizer sprayed oil droplets into a chamber where some droplets fell through the hole in the upper floor. Robert Millikan attatched a battery to the top and bottom plates where he applied an electric voltage. This determined the size of the charge on an electron as well as detrmining that there was a smallest 'unit' of charge(charge that is "quantized"). -
Ernest Rutherford
New Zealand-born British physicist discovered the nucleus of the atom in 1911, was the first to split the atom and was awarded the 1908 Nobel Prize in chemistry for his theory of atomic structure. -
Gold Foil
Helium atom particles(alpha particles) were on a piece of gold foil about 8.6x10^-6cm thick where Ernest Rutherford took observations on a screen of zinc sulphide behind the foil. He saw the deflection of the bombarded alpha particles on the photographic film. -
Cloud Chamber
A sealed environment that contains supersaturated vapor of water or alcohol. The fluid is ionized when a charged particle interacts with the mixture. Condensation nuclei is the resulting ions where a mist will form. Discovered by C.T.R. Wilson -
Bohr Model
First introduced by Niels Bohr, the model shows that the atom is small, positively charged nucleus that is surrounded by electrons that orbit around the nucleus in a similar way to the solar system, but with attraction due to electrostatic forces rather than gravity. -
Line Spectra
The result of interaction between a quantum system and a single photon. The photon is absorbed when a photon has about the right amount of energy to allow a change in the energy state of the system. It will then be re-emitted, either in the same frequency as the original or in a cascade, and the sum of the photons' energies emitted will equal the energy of one absorbed. Discovered by Niels Bohr. -
Werner Heisenberg
German physicist and philosopher who discovered (1925) a way to formulate quantum mechanics in terms of matrices. The theory and applications resulted in the discovery of allotropic forms of hydrogen. -
Erwin Schrödinger
Developed a powerful model of the atom in 1926, generated a mathematical model for distribution of electrons in an atom. -
Louis de Broglie
French physicist who predicted the wave nature of electrons. He was awarded the 1929 Nobel Prize for Physics. -
Beryllium Radiation
After an experiment conducted by Irène and Frédéric Joliot-Curie, Rutherford and Chadwick believed that beryllium was producing neutrons. The experiment let radiation hit a block of paraffin wax which caused the wax to produce protons. After measuring the speeds of the protons, they found that the gamma rays needed to be very energetic to knock them off of the wax. -
James Chadwick
English physicist who was awarded the 1935 Nobel Prize in Physics for his discovery of the neutron in 1932
