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460
Democritus
His idea was that there are smallest indivisible bodies from which everything else is composed and moves about in an infinites void space. He rationalised the different laws of chemical combination that were in existence at that time. -
Newton
He proposed a mechanical universe with small solid masses in motion and said that forces held atoms together. -
Dalton
He said that: all matter is composed of atoms and can’t be made or destroyed, atoms with the same element are identical and different elements have unlike types of atoms, chemical reactions can happen when atoms are rearranged and compounds are made from atoms of the constituent elements. His theory explained a lot of other things that were unexplained at that time. -
G.J. Stoney
He put forward the idea that electricity was made of electrons, which are discrete negative particles. He started the idea was using symbols to represent the elements and he contributed into find out the exact atomic weight. -
J.J. Thomson
He used a CRT to experimentally find out the charge: mass (ratio) (e/m) of an electron which is 1.759 x 10 8 coulombs/gram. -
Planck
He used the idea of quanta, which are discrete units of energy, to clarify hot glowing matter. -
Nagaoka
He suggested a "Saturnian" model of the atom with flat rings of electrons circling around a positively charged particle. -
Milikan
He conducted an oil drop experiment and determined the charge (e=1.602 x 10 -19 coulomb) and the mass (m = 9.11 x 10 -28 gram) of an electron. -
E.Rutherford
He used alpha particles as atomic bullets, probed the atoms in a piece of thin (0.00006 cm) gold foil. The nucleus was said to be: very dense, very small and positively charged. He believed that the electrons were located outside the nucleus. He was the one who suggested that the positive charged was in a nucleus and his theory led to the planetary model of the atom. -
H.G.J Moseley
He determined the charges on the nuclei of most atoms using x-ray tubes. He wrote that the atomic number of an element is the same number of protons in the nucleus. This work was used to rearrange the periodic table based upon atomic number instead of atomic mass. -
Bohr
He developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up of successive orbital shells of electrons. -
James Chadwick
He found out that a neutral atomic particle with a mass close to a proton, using alpha particles. The neutron was discovered.
