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Democrtius
He was the first to use the term atom and proposed that atoms were mechanically bound. It seemed to him that if atoms stayed together they did it with a system like a hook and eye. -
John Dalton
He discovered that certain gases only could be combined in certain proportions even if two different compounds shared the same common element or group of elements. Through deductive reasoning and experimentation, he made an interesting discovery. His findings led him to hypothesize that elements combine at the atomic level in fixed ratios. -
J.J. Thomson
J. J. Thomson considered that the structure of an atom is something like a raisin bread, so that his atomic model is sometimes called the raisin bread model. He assumed that the basic body of an atom is a spherical object containing N electrons confined in homogeneous jellylike but relatively massive positive charge distribution whose total charge cancels that of the N electrons. The schematic drawing of this model is shown in the following figure. Thomson's model is sometimes dubbed a plum pudd -
Hantaro Nagaoka
In 1904, Nagaoka developed an early planetary model of the atom.[1] Nagaoka's model was based around an analogy to the explanation of the stability of the Saturn rings (the rings are stable because the planet they orbit is very massive). The model made two predictions: 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
Rutherford directed the famous Geiger-Marsden experiment in 1909, which suggested, upon Rutherford's 1911 analysis, that the so-called "plum pudding model" of J. J. Thomson of the atom was incorrect. Rutherford's new model[1] for the atom, based on the experimental results, contained the new features of a relatively high central charge concentrated into a very small volume in comparison to the rest of the atom and with this central volume also containing the bulk of the atomic mass of the atom. -
Niels 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. -
Werner Heisenberg & Erwin Schrodinger
Classical physics had always assumed that precise location and velocity of objects was always possible. Heisenberg, however discovered that this was not necessarily the case at the atomic level. In particular, he stated that the act of observation interfered with the location and velocity of small particles such as electrons. Erwin Schrodinger took the ideas developed by de Broglie, Heisenberg and others and put them together in a single equation that is named after him. Solving this equation ca -
James Chadwick
In 1932 the English physicist James Chadwick discovered the neutron. He found it to measure slightly heavier than the proton with a mass of 1,840 electrons and with no charge (neutral). The proton-neutron together, received the name, "nucleon."
The existence of neutrons explained why atoms are heavier than the total mass of their protons and electrons.
