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Matter is made of small indivisible particles which have different form, position and arrangements. Democritus named these particles atoms.
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Developed an atomic theory stating that spherical atoms had measureable properties of mass. Pictures atoms as tiny, indestructible particles, with no internal structure.
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Tiny, Solid Sphere
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Observed a cathode-ray tube and found rays traveling in the direction opposite to that of the cathode rays. He called these rays canal rays and concluded that they were composed of positive particles.
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Discovers the electron and used cathode ray tubes to determine the charge to mass ration of an electron to be 1.759 x 10^8 Coulombs/gram. Found canal rays were associate with a proton, H+. He pictures electron embedded in a sphere of positive electrical charge.
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- Sphere with posotive charge throughout
- Negatively charged particle (electron)
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Discovers alpha and beta rays emitting from radium. First artifically induced nuclear reaction. Used nitrogen and alpha particles to obtain an oxygen isotope and protons. Finds that an atom has a small, dense, positively charged nucleus. Electrons move around the nucleus.
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Orbits = path of a moving electron
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Publishes papaer regarding combining nuclear and quantum theories. The electron moves in a circular orbit at fixed distances from the nucleus.
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An electron can gain or lose energy by changing its orbit.
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The U.S physicist carried out experiments to find the quantity of charge carried by an electron. Calculated the mass of the electron.
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Saw electrons as a continuous cloud and developed wave mechanics to be a mathematical model for the atom.
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- The electron cloud is a visiial model of the probable locations of electrons in an atom. The probability of finding an electron is higher in the denser regions of the cloud.
- The nucleus contains protons and neutrons.
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English physicist, confirms the existence of neutrons, which have no charge. Atomic nuclei contain neutrons and positively charged protons.
