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John Dalton
Elements are made of extremely small particles called atoms.
Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.
Atoms cannot be subdivided, created, or destroyed.
Atoms of different elements combine in simple whole-number ratios to form chemical compounds.
In chemical reactions, atoms are combined, separated, or rearranged. -
J.J. Thomson
Earlier, physicists debated whether cathode rays were immaterial like light ("some process in the aether") or were "in fact wholly material, and ... mark the paths of particles of matter charged with negative electricity", quoting Thomson. The aetherial hypothesis was vague, but the particle hypothesis was definite enough for Thomson to test.
In 1904 Thomson suggested a model of the atom, hypothesizing that it was a sphere of positive matter within which electrostatic forces determined the p -
Hantaro Nagaoka
a very massive nucleus (in analogy to a very massive planet)
electrons revolving around the nucleus, bound by electrostatic forces (in analogy to the rings revolving around Saturn, bound by gravitational forces). -
Ernest Rutherford
Deflcted alpha partiles passing through thin gold foil A vary small charged nucleus contaning much of an atom's mass was orbited by law mass electrons -
Neils Bohr
"Bohr Model" proposed that energy levels of electrons are discrete
*Electrons revolve in stable orbits around the atomic nucleus
*Electrons can jump from one energy level to another -
Werner Heisenberg & Edwin Schrodinger
*The electron could now be described by four wave functions, satsfying four simultaneous differential equations.
* Electrons still cannot be probability outside the nucleus. -
James Chadwick
1935- Nobel Prize in Physics for discovery of neutron 1932- Dizcovered the neutron
