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John Dalton
A British chemist and physicist, developed a theory that matter is simply composed of atoms of different weights and is combined in ratios by weight. Also proposed that these atoms are spherical, and are in motion. -
Dalton´s Model
A composition of previous findings by Democritus and his own findings. He included in this theory that all matter is made of atoms, that atoms cannot be created nor destroyed and also, atoms of different elements combine in whole ratios to form chemical compunds. His theory would later contribute to an advance in the atomic model. -
J.J. Thompson
Was the first to discover the electron. Used a CRT to experimentally determine the charge to mass ratio (e/m) of an electron =1.759 x 10 8 coulombs/gram. Studied "canal rays" and found they were associated with the proton H + . -
J.J. Thompson´s Model
Up until his time, all models of the atom looked like a big solild ball. J.J. Thomson discovered the electron, which led him to create the "plum pudding" atomic model. In this model, he thought that the atom was mostly positive, and negative electrons wandered around the atom. The "plum pudding" model influenced other scientists to make better atomic models. -
William Crookes
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. -
Ernest Ruthenford
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. Discovered alpha, beta, and gamma rays in radiation. -
Rutherford Model
Felt that J.J. Thomson's model was incorrect, so he created a new one. He created the nucleus, and said that instead of the positive matter being the whole atom, it was just in the middle. He said the atom was mostly empty space and that the electrons surrounded the positive nucleus. This model influenced one of his own students to perfect the atomic model later on. -
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. Proposed an atomic structure theory that stated the outer orbit of an atom could hold more electrons than the inner orbit. Created a model of successive orbital shells based o an equation of fixed radii and quantum numbers. -
Bohr´s Model
Bohr's Model puts electrons in shells that orbit the small, positively charged nucleus of the atom. Visualize this model as similar in structure to the solar system, but with electrostatic forces providing attraction, rather than gravity. -
James Chadwick
Using alpha particles discovered a neutral atomic particle with a mass close to a proton. Thus was discovered the neutron. -
Quantum Mechnical Model
Based on quantum theory, which says matter also has properties associated with waves. According to quantum theory, it’s impossible to know the exact position and momentum of an electron at the same time. This is known as the Uncertainty Principle. The quantum mechanical model of the atom uses complex shapes of orbitals (sometimes called electron clouds), volumes of space in which there is likely to be an electron. So, this model is based on probability rather than. -
BIBLIOGRAPHY - didn´t fit in most descriptions of events.
http://en.wikipedia.org/wiki/History_of_quantum_mechanics
http://www.dummies.com/how-to/content/atomic-structure-the-quantum-mechanical-model.html
http://answers.yahoo.com/question/index?qid=20100101200037AAaVFgm
http://en.wikipedia.org/wiki/James_Chadwick
http://en.wikipedia.org/wiki/J._J._Thomson
http://en.wikipedia.org/wiki/John_Dalton
http://en.wikipedia.org/wiki/Ernest_Rutherford
http://en.wikipedia.org/wiki/William_Crookes
atomictimeline.net/index.php
