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Aristotle proposes the four element theory that any visible object is made up of either air, water, fire or earth.
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Greek philosophers, Leucippus and Democritus developed the idea of atoms, that all particles are made up of matter.
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Isaac Newton propsed a mechanical universe with small solid masses in motion.
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Antoine Lavoisier constructed the first list of 33 elements, distinguishing between metals and non-met
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John Dalton proposed ‘Dalton’s Law’ stating that in a mixture of non-reacting gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases.
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Jakob Berzellus developed a table of atomic weights for the elements and introduced letters to symbolize them.
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John Newlands an English chemist proposed the law of octaves which stated that elements repeated their chemical properties every eighth element.
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JJ Thompson discovered the electrons, using properties of cathode rays.
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Ernest Rutherford established that the nuclear charge on a nucleus was proportional to the atomic weight of the element.
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Henry Moseley determined the atomic number of each element and modified the periodic law.
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Niels Bohr developed the Bohr atomic model, with electrons travelling in orbits around the nucleus and chemical properties determined by how many electrons are in the outer orbit.
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Niels Bohr developed an explanation of atomic structure, and built a an atomic model that had atoms make up of successive orbital shells of electrons.
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James Chadwick using alpha particles discovered a neutral atomic particles with a mass close to a proton and so the neutron was made.
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John Newlands arranged the elements in order of atomic weight, observing the similarities of the elements.
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Dimtri Mendeleev started the development of the periodic table arranged the elements by atomic weight and properties. The table contained 17 columns with two periods of seven elements.
