-
101
Democritus
Democritus' only belief about atoms was that they were one of the possibilities when debating the structure of matter.
He believedIf liquid atoms were like little balls they would roll out when you tip the container.
Believed solide were hard and rigid. -
John Dalton
Believed that
1) All matter is made of atoms. Atoms are indivisible and indestructible.
2) All atoms of a given element are identical in mass and properties
3) Compounds are formed by a combination of two or more different kinds of atoms.
4) A chemical reaction is a rearrangement of atoms. -
J.J. Thomson
Thomson, in 1897, was the first to suggest that the fundamental unit was over 1000 times smaller than an atom, suggesting the subatomic particles now known as electrons. Thomson discovered this through his explorations on the properties of cathode rays. Thomson made his suggestion on 30 April 1897 following his discovery that Lenard rays could travel much further through air than expected for an atom-sized particle.[ -
Ernest Rutherford
In 1899 Ernest Rutherford studied the absorption of radioactivity by thin sheets of metal foil and found two components: alpha (a) radiation, which is absorbed by a few thousandths of a centimeter of metal foil, and beta (b) radiation, which can pass through 100 times as much foil before it was absorbed. Shortly thereafter, a third form of radiation, named gamma (g) rays, was discovered that can penetrate as much as several centimeters of lead. -
Hantaro Nagaoka
developed the earliest published quasi-planetary model of the atom. This graduate of the University of Tokyo from 1887 spent his postdoctoral period in Vienna, Berlin and Munich before obtaining a professorship in Tokyo to become Japan's foremost modern physicist. Nagaoka assumed that the atom is a large, massive, positively charged sphere, encircled by very many (in order of magnitude: hundreds) light-weight, negatively charged ► electrons, bound by electrostatic forces analogous to Saturn's ri -
Neils Bohr
the Bohr model, introduced by Niels Bohr in 1913, depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus—similar in structure to the solar system, but with electrostatic forces providing attraction, rather than gravity.The Bohr model gives almost exact results only for a system where two charged points orbit each other at speeds much less than that of light. -
Werner Heisenberg & Erwin Schrodinger
Heisenberg’s uncertainty principle states that it is “not possible to obtain precise values of both poison and momentum of a particle at the same time (website link at bottom).” the electron cloud model represents his principle since the only way to find the location of an electron with in an atom is through the means of probability. -
James Chadwick
In 1932, James Chadwick performed a series of experiments at the University of Cambridge, showing that the gamma ray hypothesis was untenable. He suggested that the new radiation consisted of uncharged particles of approximately the mass of the proton, and he performed a series of experiments verifying his suggestion.he also discovered the neutron
