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John Dalton proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass.
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Discovered cathode rays had the following properties: travel in straight lines from the cathode; cause glass to fluoresce; impart a negative charge to objects they strike; are deflected by electric fields and magnets to suggest a negative charge; cause pinwheels in their path to spin indicating they have mass.
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Using a CRT he observed that nearby chemicals glowed. Further experiments found very penetrating rays coming from the CRT that were not deflected by a magnetic field. He named them "X-rays".
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While studying the effect of x-rays on photographic film, he discovered some chemicals spontaneously decompose and give off very pentrating rays.
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Studied radiations emitted from uranium and thorium and named them alpha and beta.
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Ued the idea of quanta (discrete units of energy) to explain hot glowing matter.
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Oil drop experiment determined the charge (e=1.602 x 10 -19 coulomb) and the mass (m = 9.11 x 10 -28 gram) of an electron.
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Thomson’s model was known as the "Plum Pudding Model” (or "Raisin Bread Model.") As each atom was a sphere filled with a positively charged fluid, known as the “pudding”. Scattered in this fluid were negatively charged electrons, these were the “plums” in the pudding. Thomson suggested that the positive fluid held the negatively charged electrons in the atom because of its electrical forces.
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Published the famous equation E=mc 2
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Developed an electrical device to "click" when hit with alpha particles.
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Using alpha particles as atomic bullets, probed the atoms in a piece of thin (0.00006 cm) gold foil . He established that the nucleus was: very dense,very small and positively charged. He also assumed that the electrons were located outside the nucleus.
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In 1911 Ernest Rutherford was the first scientist to find out that every single atom does have a nucleus. With that information, he also found out that the nucleus is mostly space and nothing else. With this discovery, it allowed other scientists to dig further down with their research of the atom. It also helped see that the atom is more than just a dense ball. It has an advanced molecular structure. All of this then led to explanations of nuclear physics.
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In 1913, Niels Bohr proposed the "Solar System" model of the atom, also known as the Rutherford-Bohr model, because it was a modification of Rutherford's model. This modification was based off of quantum physics. The model is similar to a solar system: electrons revolve around the nucleus like planets revolving around the sun. However, instead of gravity being the force of attraction, electrostatic forces keep the electrons in orbit.
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Developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up of sucessive orbital shells of electrons.
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In the mid-1920s, an Austrian scientist named Erwin Schrödinger thought that the problem with Bohr’s model was restricting the electrons to specific orbits. He wondered if electrons might behave like light, which scientists already knew had properties of both particles and waves. Schrödinger speculated that electrons might also travel in waves.
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Viewed electrons as continuous clouds and introduced "wave mechanics" as a mathematical model of the atom.
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Using alpha particles discovered a neutral atomic particle with a mass close to a proton. Thus was discovered the neutron.
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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.
