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The 3 Laws
In the 1790's, the study of matter was revoltuionized by a new emphasis on on the quantitve analysis of chemical reactions. This led to the discovery of 3 new laws: the law of conservation of mass, the law of definite proprtions, and the law of multiple proportions. -
Dalton's Atomic Theory
John Dalton, a school teacher, proposed a new theory that encompassed all the laws together. His theory can be summed up in 5 statements. He reasoned that elements are composed of atoms and that only whole number of atoms can combine to form compounds. -
Cathode Rays
Joseph John Thompson supported the hypothesis that the particles that compose cathode rays are negatively charged with experiments. In one experiment he was able to measure the ratio of the charge of cathode ray particles to their mass. -
Charge and Mass of the Electron
Robert A. Millikan measure the charge of the electron. Thompson proposed a model for the atom that is called the Plum Pudding Model. He believed that the negative electrons were spread evenly throughout the psoitive charge of the rest of the atom. -
The Atom's Structure
Ernest Rutherford and his associates Hans Geiger and Ernest Marsden provided more detail of the structure of the atom. Geiger and Marsden found that roughly 1 in 8000 of the alpha particles has been reflected back to the toward the source when they checked for the possibility of wide-angle deflections. Rutherford concluded that this force must be caused by a very densely packed bundle of matter with a poitive charge, the nucleus. -
Atomic Structure
Neils Bohr applied the quantum theory to Rutherford's atomic structure by assuming that electrons travel in stationary orbits defined by their angular momentum. This led to the calculation of possible energy levels for these orbits and the postulation that the emission of light occurs when an electron moves into a lower energy orbit. -
Isotopes
Frederick Soddy formulates the concept of isotopes, which states that certain elements exist in two or more forms which have different atomic weights but which are indistinguishable chemically. -
Matter Has Waves
Louis de Broglie believed that matter can behave like waves and waves can behave like particles. His theory was questioned, but Albert Einstein later proved it right. -
Quantum Mechanics
Paul Adrien Maurice Dirac, in a series of four definitive papers, makes a major contribution to physics by devising a form of quantum mechanics, the laws of motion that govern atomic particles. Dirac had the revolutionary idea that the electron could be described by four wave functions, satisfying four simultaneous differential equations. It followed from these equations that the electron must rotate on its axis, an idea that had been developed by other physicists, and also that there must be st -
The Positron
Paul Dirac wave equation predicted the existence of antimatter as it required the existence of an unknown kind of particle with the same mass and opposite charge to an electron. -
The Neutron
James Chadwick discovered the neutron by repeating a previous experiment but looking for a neutral particle. His experiments were successful. -
Protons and Neutrons
E.C.G. Stückelberg observes that protons and neutrons do not decay into any combination of electrons, neutrinos, muons, or their antiparticles. The stability of the proton cannot be explained in terms of energy or charge conservation; he proposes that heavy particles are independently conserved. -
The Nucleon
C. Moller and Abraham Pais introduce the term "nucleon" as a generic term for protons and neutrons. -
Nuclear Fission Bomb
The first nuclear fission bomb is exploded at the Trinity test site, about sixty miles Northwest of Alamogordo, New Mexico. Fission bombs are also known as atom bombs and create energy by splitting the nucleus of heavy elements such as Uranium and Plutonium. -
Nuclear Shell
The 1963 Nobel Laureate in Physics is awarded to Maria Goeppert-Mayer and Johannes Hans Daniel Jensen for their discoveries concerning nuclear shell structure. Since 1948, Maria Goeppert-Mayer had worked on nuclear shell structure and the meaning of the "magic numbers" - those nuclei that have a special number of protons. She postulated these numbers to be the shell numbers of a shell model, a "nuclear counterpart to the closed shells of electrons" at the atomic level.
