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460 BCE
Democritus
He explained that the original motion of the atoms was in every direction, therefore there were collisions and a whirling movement, where similar atoms were brought together and united to form larger bodies and worlds.Democritus was also the first to attempt to explain colour, which he thought was due to the position of the atoms. -
John Dalton
He based his theory of partial pressures on the idea that atoms that are alike will repel one another in a mixture of gases, whereas unlike atoms appear to react indifferently to each other. He argued that each element had its own kind of atom. -
Dmitri Mendeleev
Mendeleev found that, when all known chemical elements were arranged in order of increasing atomic weight, the resulting table displayed a recurring pattern, or properties within groups of elements. He discovered the periodic law. -
Eugene Goldstein
In 1886 he discovered canal rays, also called positive rays. He also contributed greatly to the study of cathode rays; in 1876 he showed that the rays could cast sharp shadows, and they were emitted perpendicular to the cathode surface. -
J.J Thomson
Thomson’s discovery of the electron was the result of an attempt to solve a controversy regarding the nature of cathode rays. Thomson was able to put forward that the rays were composed of the same particles, regardless of what kind of gas carried the electric discharge. -
Robert Millikan
Milikan began a series of experiments to determine the electric charge carried by a single electron. The results suggested that the charge on the droplets is a multiple of the elementary electric charge -
Ernest Rutherford
Rutherford was the central figure in the study of radioactivity. He turned his attention to the other elements that were known to be radioactive. He and a colleague found that thorium emitted a gaseous radioactive product, which he called emanation. -
Niels Bohr
Rutherford and his collaborators established that the atom consists of a heavy positively charged nucleus with substantially lighter negatively charged electrons circling around it. -
James Chadwick
Chadwick interpreted that radiation as being composed of particles of mass approximately equal to the proton but without an electrical charge. This discovery provided a new tool for including atomic disintegration since neutrons could undeflected into the atomic nucleus.
