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The Alchemists in 500BC through 1720 developed the theory that all metals are composed of mercury and sulfur and that it is possible to change base metals to gold.
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Aristotle did not believe in the atomic theory and he taught so otherwise. He thought that all materials on Earth were not made of atoms, but of the four elements, Earth, Fire, Water, and Air. He believed all substances were made of small amounts of these four elements of matter. His views about elements are incorrect.
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Plato introduced the atomic theory in which ideal geometric forms serve as atoms, according to which atoms broke down mathematically into triangles, such that the form elements had the following shape: fire (tetrahedron), air (octahedron), water (icosahedron), earth (cube).
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Democritus was a central figure in the development of the atomic theory of the universe. He theorized that all material bodies are made up of indivisibly small “atoms.” Aristotle famously rejected atomism in On Generation and Corruption.
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"1. Daltons Atomic Theory states that all elements are composed of atoms that are indivisible (they can not be created, divided, or destroyed)
2. All atoms of the same element are identical.
3. Atoms of different elements are different (they always have different numbers of protons and they may also differ in mass numbers.
4. Atoms of different elements can combine with each other in simple whole number ratios to form compounds" -Chemistry Notes -
Boyle's Law states that if the volume of a gas is decreased, the pressure increases proportionally. Understanding that his results could be explained if all gases were made of tiny particles, Boyle tried to construct a universal 'corpuscular theory' of chemistry.
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Antoine Lavoisier created the Law of Conservation of Mass
This states that mass is neither created nor destroyed in chemical reactions. We now understand why matter is conserved -- atoms are neither created nor destroyed in a chemical reaction. -
Mendeleev created the first Periodic Table. The Periodic Law states that when elements are arranged according to their atomic number, elements with similar properties will appear at regular intervals.
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John Dalton was incorrect that the atom was invisible. J.J. Johnson made this discovery and also revised other parts of Dalton's atomic model. Electrons were also founded by J.J. Johnson.
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French physicists Pierre and Marie Curie discovered the strongly radioactive elements polonium and radium, which occur naturally in uranium minerals. Marie coined the term radioactivity for the spontaneous emission of ionizing, penetrating rays by certain atoms.
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Einstein mathematically proved the existence of atoms and he helped revolutionize all the sciences through the use of statistics and probability.
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His earliest major success was the accurate determination of the charge carried by an electron, using the elegant “falling-drop method”; he also proved that this quantity was a constant for all electrons, thus demonstrating the atomic structure of electricity.
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Ernest Rutherford found and named the nucleus. He found this information out by doing an experiment. He used a sheet of gold foil and aimed a beam of alpha particles. He noticed a few of the particles were greatly deflected.
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Mosely used self-built equipment to prove that every element's identity is uniquely determined by the number of protons it has. His discovery revealed the true basis of the periodic table and enabled Moseley to predict confidently the existence of four new chemical elements, all of which were found.
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In 1913, Niels Bohr proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined quantities. Electrons should move around the nucleus but only in prescribed orbits. When jumping from one orbit to another with lower energy, a light quantum is emitted. Bohr's theory could explain why atoms gave off light in fixed wavelengths.
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Werner Heisenberg contributed to atomic theory through formulating quantum mechanics in terms of matrices and in discovering the uncertainty principle, which states that a particle's position and momentum cannot both be known exactly.
