Democritus - Proposed that all matter is made up of tiny, invisible particles called atoms, Boyle - Defined the word element, Priestley - Discovered oxygen, Lavoisier - Law of Conservation of Mass, Proust - Law of Definite Proportions, Dalton - Proposed Atomic Theory of Matter, Franklin - Concluded that there are two kinds of electrical charges, positive & negative, Faraday - Proposed the structure of atom is related to its electricity, Thomson - Defined what electrons are & determined the ratio of the electron charge to an atom’s mass, Millikan - Determined the mass of an electron, Becquerel - Discovered radioactivity, Rutherford - Concluded that the atom is mostly empty space with a very tiny, positively charged, dense center he called the nucleus., Bohr - Stated that electrons travel around the nucleus in fixed orbits., Moseley - Named the individual positive charged proton, Chadwick - Discovered the existence of neutrons, Planck - Proposed the relationship between a quantum of energy and the frequency of radiation., Einstein - Introduced electromagnetic radiation has a dual wave-particle nature. Also defined the term photons, particles of light carrying a quantum of energy, Broglie - Suggested that electrons be considered waves confined to the space around an atomic nucleus, Heisenburg - Uncertainty principle: it is impossible to determine simultaneously both the position and velocity of an electron or any other particle, Schrödinger - Developed an equation that treated electrons in atoms as waves that would give the probability of finding an electron at a given place around the nucleus,

Atomic History Scientist

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