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In 430 B.C , Democritus proposed the first idea of the atom. The atomic theory stated that “The universe is composed of two elements: the atoms and the void in which they exist and move.”
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Proposed a mechanical universe with small solid masses in motion.
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LaVoiser discovered what is known as the Law of Conservation of Mass which states that matter is conserved in a chemical reaction. Atoms are neither created or destroyed, but it can be rearranged.
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He published his Law of Definite Proportions that a compound is composed of exact proportions of elements by mass regardless of how the compound was created.
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John Dalton pictures atoms as tiny, indestructible particles, with no internal structure.
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A british scientist, discovers the electron, leading to his "plum-pudding" model. He pictures electrons embedded in a sphere of positive electric charge.
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A Japanese physicist, suggests that an atom has a central nucleus. Electrons move in orbits like the rings around Saturn.
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States that an atom has a dense, positively charged nucleus. Electrons move randomly in the space around the nucleus.
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In his model, the electrons move in spherical orbits at fixed distances from the nucleus.
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Proposed that moving particles like electrons have some properties of waves. Within a few years, evidence is collected to suport this idea.
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Develops mathematical equations to describe the motions of electrons in atoms. His work leads to the electron cloud model.
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A british physicist who confirmed that the existence of neutrons, which have no charge. Atomic Nuclei contain neutrons and positively charged protons.
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Conducted experiments verifying that heavy elements capture neutrons and form unstable products which undergo fission. This process ejects more neutrons continuing the fission chain reaction.
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Synthesized 6 transuranium elements and suggested a change in the layout of the periodic table.
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Conducted the first controlled chain reaction releasing energy from the atoms nucleus.
