-
101
Democritus
The Democritus Atomic Theory revolves around the atoms that are present in the atmosphere. -
101
Ernest Rutherford
Ernest Rutherford publishes his atomic theory describing the atom as having a central positive nucleus surrounded by negative orbiting electrons. -
101
Neils Bohr
by assuming that electrons travel in stationary orbits defined by their angular momentum. This led to the calculation of possible energy levels for these orbits and the postulation that the emission of light occurs when an electron moves into a lower energy orbit. -
Jan 1, 600
Werner Heisenberg & Erwin Schrodinger
This beam can be fired at a a fluorescent screen by placing a small electrode a few centimetres away from the heated element and connecting a voltage between the element and the electrode. The electrode has to be positive (anode) and the element has to be negative (cathode). *
The invisible beam produces a bright dot on the screen. The beam is known as a cathode ray. Because the beam is attracted to the anode, Thomson deduced that cathode rays were a stream of negative particles. He called th -
john dalton
Dalton's theory was based on the premise that the atoms of different elements could be distinguished by differences in their weights. -
J.J. Tomson
When a maltese cross was placed in its path, a shadow of the cross was seen on the wall of the tube opposite to the cathode.. If the cross was lowered, its shadow disappeared. Thus it was found out that electrons travelled in a straight line. -
Hantaro Nagaoka
On the other hand, the model of Nagaoka led to speculation that the electrons turning around the atomic nucleus would slowly lose energy and ultimately collide with the nucleus. For this model to be correct, an explanation had to be found why this was not happening. There was no experimental proof, and moreover, it was not supported, except by some scholars, such as Lodge and Poincare. -
James Chadwick
s of 1918, with Ernest Rutherford’s discovery of the positively-charged proton, it surely seemed to many physicists as if a nearly complete model of the atomic structure was at hand. After all, there was the electron (discovered by J.J. Thompson in 1897) which was tiny and seemed to buzz a “solar-system”-like orbit around the atomic nucleus (discovered by Rutherford, Geiger, and Marsden in 1909), which contained the proton – a particle much denser and more massive than the tiny electron, but wit
