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Atomic Model/Theory Timeline Project
Transcript of Atomic Model/Theory Timeline Project
Period 5 Steps to the Current Atomic Model Empedocles (490-430 B.C.) J.J. Thomson discovered the electron by passing an electric current through gases at low pressure in a sealed glass tube. A glowing beam known as the cathode ray traveled from the the negatively charged end to the positively charged end. He concluded it was a stream of negatively charged particles called electrons. 1897 Luis se Broglie came up with the wave-particle theory which states that particles of matter move in a wave like fashion. This attempted to explain why there are discrete energy levels in an electron. 1923 James Chadwick discovered the neutron and was awarded the Nobel peace prize. This discovery was important because it completely revolutionized the way that scientists viewed the atomic nucleus. 1932 Empedocles proposed that there were four fundamental substances that accounted for all matter. Earth, air, fire, and water were the first ideas of elemental substances. Leucippus (475 B.C.) Leucippus developed the idea that everything is made up indivisible particles called atoms. His student, Democritus, recorded his atomic theory which states that atoms are homogeneous, solid, and unchangeable. He also claimed that changes in matter result from different groupings of atoms. In addition, different kinds of atoms differ in size and shape. His theory also explains that the properties of matter reflect the properties of the atoms contained in the matter. Democritus (460- 370 B.C.) Democritus supported his teacher's theory that everything is composed of indivisible atoms. However, he believed that the shapes and arrangement of atoms accounted for different materials. He also hypothesized that atoms were in perpetual motion in a void of space. He created the explanation of the changes that occur when matter is transformed chemically. Plato (427- 347 B.C.) Plato expanded the atomic theory to mathematical objects and empty space. He proposed that each kind of matter- earth, air, fire, and water- was made up of particles specific to the kind of matter. These geometric solid particles were then composed of right triangles. Aristotle (384-322 B.C.) Aristotle developed the idea that all kinds matter-earth, air, fire, and water- were composed of four opposites. These opposites were hot and cold, and wet and dry. He also discussed the properties of real substances, their elemental compositions, and how they reacted to other substances. 1776 American colonies declared independence from Great Britain on July 4, 1776. 1803 1911 1913 1916 1920 The Nineteenth Amendment was ratified giving women the right to vote in all United States elections. works sighted John Dalton transformed Democritus's ideas about atoms into a scientific theory that included the following points: all elements are composed of atoms, atoms of one element differ from those of another element, atoms can physically mix and chemically combine to form compounds, and chemical reactions occur when atoms are rearranged. Dalton also discovered that atoms never change into atoms of a different element. Ernest Rutherford discovered the the nucleus of the atom by directing a beam of alpha particles at a thin sheet of gold foil. Based on the deflection of the particles, he concluded most of the atom was empty space. However, he also discovered that all of the positive charge and most of the atom's mass was centered in a small region that he called the nucleus. Neils Bohr improved the atomic model by proposing that electrons circle the nucleus in paths or orbits. Each orbit had a fixed energy level. In order for atoms to move from one level to the next, they would have to gain or lose just the right amount of energy. This amount is known as a quantum of energy. Cassidy, David. "The Uncertainty Principle." Heisenberg - Quantum Mechanics. American Institute of Physics, n.d. Web. 30 Sept. 2012. <http://www.aip.org/history/heisenberg/p08.htm>.Lloyd, G. E. R. Early Greek Science: Thales to Aristotle,. London: Chatto & Windus, 1970. Print.
"ChemTeam: Thomson Model of the Atom." ChemTeam: Thomson Model of the Atom. N.p., n.d. Web. 30 Sept. 2012. <http://www.chemteam.info/AtomicStructure/Thomson-Model-Intro.html>.
Francis, Eden. "Dalton's Atomic Theory." Dalton's Atomic Theory. N.p., 2002. Web. 30 Sept. 2012. <http://dl.clackamas.cc.or.us/ch104-04/dalton's.htm>.
"Leucippus and Democritus." Leucippus and Democritus. N.p., n.d. Web. 29 Sept. 2012. <http://chemed.chem.purdue.edu/genchem/history/leucippus.html>.
"The Oil Drop Experiment." The Oil Drop Experiment. N.p., n.d. Web. 29 Sept. 2012. <http://ffden-2.phys.uaf.edu/212_fall2003.web.dir/ryan_mcallister/slide3.htm>.
"People and Discoveries." A Science Odyseey. PBS, n.d. Web. 30 Sept. 2012. <http://www.pbs.org/wgbh/aso/databank/entries/dp13at.html>.
Russell, Bertrand. A History of Western Philosophy. New York, NY: Simon and Schuster, 1972. Print.
Senese, Fred. "Glossary: L." General Chemistry Online: Glossary:. N.p., 2 May 2010. Web. 29 Sept. 2012. <http://antoine.frostburg.edu/chem/senese/101/glossary/l.shtml>. John Dalton's atomic structure. J.J. Thomson's model displayed electrons like negatively charged raisins in a positively charged dough. Rutherford's atomic model is composed of a positively charged nucleus surrounded by moving electrons. The Bohr atomic model displays electrons orbiting the nucleus at fixed distances dependent upon energy levels. 1926 Erwin Schrodinger developed the concept of atomic orbital as well as the idea of sub orbitals. He believed that they were in geometric shapes which reinforces the wave theory. His work paved the way for the electron cloud model. 1927 Heisenberg came up with the uncertainty principle which basically states that it is impossible to know exactly where a particle is and how much it weighs at the same time because the very act of measuring an electron changes its velocity and its location. 1933 Adolf Hitler was named German chancellor, inevitably causing World War II. 1865 President Abraham Lincoln was assassinated by John Wilkes Booth on April 15, 1865. Robert A. Millikan found the mass and quantity of charge carried by an electron. He discovered an electron is 1/1,840 the mass of a hydrogen atom and has one unit of negative charge. He calculated these values by measuring how strong an applied electric field had to be in order to stop an oil drop from falling. 1918 plank comes up with a quantum theory which states that electrons can only have certain amounts of energy. This explained why energy is absorbed or eliminated only in discrete amounts. 1969 Neil Armstrong was the first man to walk on the moon on July 20, 1969.