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400
Democritus
B.C
His suggested theory was that all matter consists of invisible particles called atoms and that these atoms are indestructible,solid but invisible, homogenous, and that they are different in size, shape, mass, position, and arrangement. -
Antoine Lavoisier
He found that mass is conserved in a chemical reaction and his findings lead to the law of conservation of matter, which states that matter is conserved in a chemical reaction.
Between 1772-1794 -
John Dalton
1803 He proposed his atomic theory which states, All matter is made of atoms and atoms are indivisible and indestructible, all atoms of a given element are identical in mass and properties, compounds are formed by the combination of at least two different kinds of atoms, and A chemical reaction is simply the rearrangement of atoms. -
Dmitri Mendeleev
He was a Russian chemist and inventor. He formulated the Periodic Law, created his own version of the periodic table of elements, and used it to correct the properties of some already discovered elements and also to predict the properties of eight elements yet to be discovered. -
Eugen Goldestein
Eugen Goldstein was a German physicist. He was an early investigator of discharge tubes, the discoverer of anode rays, and is sometimes credited with the discovery of the proton. -
J.J Thomson
He discovered the electron in a series of experiments dealing with electric discharge in a high-vacuum cathode-ray tube. -
Max Planck
German theoretical physicist who originated quantum theory, which won him the Nobel Prize in Physics in 1918. -
Ernest Rutherford
New Zealand-born British physicist who became known as the father of nuclear physics. Discovers a radioactive gas, later to be named radon in 1988. Ern announces the nuclear model of the atom in 1911. -
Henry Moseley
Henry Moseley was an English physicist. Moseley's contribution to the science of physics was the justification from physical laws of the previous empirical and chemical concept of the atomic number. -
Niels Bohr
He proposed the idea for the Hydrogen atom. His theory was based on the quantum theory. His theory states that electrons move around the nucleus but only in set orbits and if an electron jumped to an orbit with a lower energy a light quantum is produced. -
Robert Millikan
Between 1908-1917
He studied the charge of an electron and proved J.J Thomson’s atomic theory correct. -
Werner Heisenberg
Werner Karl Heisenberg was a German theoretical physicist and one of the key pioneers of quantum mechanics. -
Erwin Schrodinge
discovery of new productive forms of atomic theory -
James Chadwick
1932 He discovered the neutron. In his experiment he used polonium as a source of (what he believed to be) neutrons, and bombarded wax. protons were released by the wax and he studied the protons’ behavior. He noticed the protons behaved exactly as if they had been hit by electrically neutral particles thus he discovered the neutron.
