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465
Democritus (465 BC)
First to propose that matter exists in the form of particles. Coined the term 'atoms'. -
Jan 1, 1100
Compass
Oldest written description of lodestone used as a compass. -
Torricelli, Evangelista (1643)
Invented the mercury barometer. -
Small Solid Matter
Proposed a mechanical universe with small solid masses in motion. (relates to democritus's idea) -
Le Blanc, Nicholas (1742-1806)
Invented process for making soda ash from sodium sulfate, limestone and coal. -
Franklin, Benjamin (1752)
Demonstrated that lightning is electricity. -
The first useful atomic theory
John Dalton developed the first useful atomic theory of matter. He thought of atoms as spherical solid matter based upon measurable properties of mass. -
Finding electicity in Atoms
Michael Faraday studied the effect of electricity on solutions, coined term "electrolysis" as a splitting of molecules with electricity, developed laws of electrolysis. Faraday didn't believe in the atomic theory, though. -
Maxwell, James Clerk (1859)
Described the mathematical distribution of the velocities of molecules of a gas. -
Maxwell, James Clerk (1873)
Proposed that electric and magnetic fields filled space. -
Discovery of electrons
G.J. Stoney discovered negatively charged particles which he named electrons. -
Mass ratio of electrons
J.J. Thomson used a CRT to experimentally determine the charge to mass ratio (e/m) of an electron, which is 1.759 x 10 8 coulombs/gram. (relates to discovery of electrons) -
Discovery of alpha and beta decay
Studied radiations emitted from uranium and thorium and named them alpha and beta. (related to radioactivity) -
Naming of radioactivity
Marie Sklodowska Curie studied uranium and thorium and called their spontaneous decay process "radioactivity". She and her husband Pierre also discovered the radioactive elements polonium and radium. -
Plank, Max (1900)
Stated radiation law and Planck's constant. (related to discovery of radiation) -
Discovery of isotopes and half-lives
Soddy observed spontaneous disintegration of radioactive elements into variants he called "isotopes" or totally new elements, discovered "half-life", and made initial calculations on energy released during decay. (relates to radioactivity) -
Theory of electron ring orbits
Nagaoka postulated a "Saturnian" model of the atom with flat rings of electrons revolving around a positively charged particle. -
The Geiger counter (radioactivity)
Hans Geiger developed an electrical device to "click" when hit with alpha particles. (relates to radioactivity) -
Electron mass and charge
R.A. Millikan did the oil drop experiment which determined the charge (e=1.602 x 10 -19 coulomb) and the mass (m = 9.11 x 10 -28 gram) of an electron. (relates to discovery of electrons) -
Nucleus theory
Ernest Rutherford used alpha particles as atomic bullets and 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. -
Reorganization of elements
H.G.J. Mosley, using x-ray tubes, determined the charges on the nuclei of most atoms. He wrote"The atomic number of an element is equal to the number of protons in the nucleus". This work was used to reorganize the periodic table based upon atomic number instead of atomic mass. -
Orbital shells of electrons
Niels Bohr 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. -
Discovery of neutrons
James Chadwick usied alpha particles to discovere a neutral atomic particle with a mass close to a proton, which was a neutron. -
Seaborg, Glenn (1941-1951)
Synthesized several transuranium elements and suggested a revision to the layout of the periodic table. (relates to atoms) -
Discovery of the energy chain reaction
Enrico Fermi conducted the first controlled chain reaction releasing energy from the atoms nucleus, particularly splitting a neutron. This would contribute to the making of the atomic bomb. (relates to discovery of neutrons) -
The discovery of the modern nucleus
Maria Goeppert Mayer said that nuclei with 2, 8, 20, 28, 50, 82, or 126 protons or neutrons were especially stable, and she helped explain to the public what the atomic structure looked like. She published her discoveries in 1948. She is the one that said the nucleus was made up of protons and neutrons, and the electrons orbit around the nucleus.
