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Atomic Theory Timeline

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Lizeth Valentin

on 8 November 2013

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Transcript of Atomic Theory Timeline

Democritus
Atomic Theory Timeline
Early Theories
Most theories before the 19th century weren't based on experiments
Only when scientists began to study and involve things like electricity, is when they began to develop models about atomic structure
J.J. Thomson's Cathode Ray Experiment
Calculated the magnitude of the atom
Shot heavy, positive charged alpha particles through gold foil
*EXPECTED alpha particles to have little deflection
most alpha particles went through the gold foil
Few deflected and some bounced back at wide angles
*RESULTS found that the positive charged, massive nucleus repelled the alpha particles
John Dalton

Used Greek Concept of the atom, the law of definite proportions, the law of conservation of mass, and the law of multiple proportions.
1808
English School Teacher
Rutherford's Gold Foil Experiment
Five Principles
All matter is composed of very small particles called atoms, which cannot be subdivided, created, or destroyed.
Atoms of a given element are identical in their properties.
Atoms of different elements differ in properties.
Atoms in different elements combine in simple, whole number ratios to form compounds.
Gold Foil Experiment Results
In chemical reactions, atoms are combined, separated, or rearranged but never create, destroyed, or changed.
1894-Stoney proposed that electricity was made of discrete negatively charged particles known as electrons.
By: Laurielle Bandolin, Angelica Del Rosario,
Taylor Tipton,
Lizeth Valentin

Results determined that the nucleus (positively charged) is in the center of an atom where electrons revolve around it, similar to the solar system.
Structure is called "Nuclear Atom" or "Planetary Atom"
1911
Greek philosopher
Can matter be divided into smaller denominations forever, or is there a limit?
Matter cannot be broken down forever, eventually its smallest denomination could be obtained and this would be indivisible
"atomos" - not to be cut
Niels Bohr
Dmitri Mendeleev
Touched on Rutherford's model
Electrons:
orbit the nucleus without losing energy
can only move in fixed orbits
electrons that are closer to the nucleus have lower energy while electrons with higher energy are further away
Chemists and physicists question findings on electrons, eventually leading them to the Quantum Model of the atom

Works Cited
Theory proposed a model of atom which is known as the plum pudding model
Sphere of positive charge with negatively charged electrons
Atom electrically neutral
"HISTORY OF THE ATOM FROM DEMOCRITUS TO BOHR AND SCHRÖDINGER." HISTORY OF THE ATOM FROM DEMOCRITUS TO BOHR AND SCHRÖDINGER. N.p., n.d. Web. 08 Nov. 2013. <http://profmokeur.ca/chemistry/history_of_the_atom.htm>.
J.J. Thomson's Theory
Gas pumped out of glass tube
Metal plates, electrodes, placed on ends
Positive electrode- anode, Negative electrode- cathode
When cathode ray was turned on a glowing beam came out and was deflected
Thomson's Conclusions:
Beam had particles with mass
Particles in beam had negative charge due to deflection
All atoms contain negatively charged particles, electrons
"Joseph John Thomson." Homepage of the Chemical Heritage Foundation. Chemical Heritage Foundation, n.d. Web. 06 Nov. 2013. <http://www.chemheritage.org/discover/online-resources/chemistry-in-history/themes/atomic-and-nuclear-structure/thomson.aspx>.
Created 7 groups of elements with similar properties
Discovered their properties "were periodic functions of their atomic weights"
Known as Periodic Law
G.J. Stoney
Buescher, Lee. "Atomic Structure Timeline." Atomic Structure Timeline. ScienceDept, n.d. Web. 06 Nov. 2013. <http://atomictimeline.net/>.
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