Fall.2008.MMA.Potter.Timeline

 ~Democritus Greece 460 BC-370 BC
 * Ancient-1700
 * [[image:file:///C:/Users/Mike/AppData/Local/Temp/moz-screenshot-2.jpg]][[image:file:///C:/Users/Mike/AppData/Local/Temp/moz-screenshot-3.jpg]]

Being the first to contribute to the discovery of atoms, he created a theory that there were various elements which always existed but could be rearranged into different states. Democritus formulated that matter was composed of small impenetrable particles called atoms. ~ Aristotle Emphasized that nature consisted of 4 elements; air earth fire and water. He believed that these elements were controlled by the gods. --Hera-Earth --Hades-Fire --Zeus-Air --Persephone-Water

1700-1800 ~**Sir Issac Newton** 1642-1727 Born: 25 December 1642 Died: 20 March 1727 Newton suggested an atomic theory in which atoms combined because of attractive forces between them to form solid, liquids and gases. He most famous discovery was of universal gravition. Which is -32 ft. sec squared and -9.8 meters per second squared. (http://www.answers.com/topic/sir-isaac-newton)

~ **Antoine-Laurent Lavoisier** 1743-1794 Lavoisier used careful measurement and thoughtful experiments to turn chemistry into a science. He also explained the experiments of others, such as Joseph Priestley's discovery of oxygen and Henry Cavendish's production of water from hydrogen and oxygen. Lavoisier used the results of other chemists and his own experiments to create the modern theory of fire and to explain the role of air in combustion and respiration. He was the among the first to have a clear concept of a chemical element and the first to list the known elements. He also developed the idea of naming compounds from elements. In addition, Lavoisier was the first to use and to state clearly a conservation law for mass. For these reasons, he is known as the father of modern chemistry.


 * ~Henry Cavendish** Oct.10, 1731-Feb. 1810

At the time Cavendish began his chemical work, chemists were just beginning to recognize that the "airs" which were evolved in many chemical reactions were distinct entities and not just modifications of ordinary air. Cavendish reported his own work in //Three Papers Containing Experiments on Factitious Air// in 1766. These papers added greatly to knowledge of the formation of " inflammable air" (hydrogen) by the action of dilute acids on metals. Cavendish also distinguished the formation of oxides of nitrogen from nitric acid. Their true chemical character was not yet known, but Cavendish's description of his observations had almost the same logical pattern as if he were thinking in modern terms, the principal difference being that he used the terminology of the phlogiston theory (that is, a burning substance liberates into its surroundings a principle of inflammability ). Cavendish's other great merit is his experimental care and precision. He measured the density of hydrogen, and although his figure is half what it should be, it is astonishing that he even found the right order of magnitude, considering how difficult it was to manage so intractable a substance. Not that his apparatus was crude; where the techniques of his day allowed, his apparatus (like the splendid balance surviving at the Royal Institution) was capable of refined results. Cavendish investigated the products of fermentation, showing that the gas from the fermentation of sugar is indistinguishable from the "fixed air" characterized as a constituent of chalk and magnesia by Black (both are, in modern language, carbon dioxide ). In his study of the methods of gas analysis Cavendish made one remarkable observation. He was sparking air with excess oxygen (to form oxides of nitrogen) over alkali until no more absorption took place and noted that a tiny amount of gas could not be further reduced, "so that if there is any part of the phlogisticated air of our atmosphere which differs from the rest, and cannot be reduced to nitrous acid, we may safely conclude, that it is not more than 1/120 part of the whole." As is now known, he had observed the noble gases of the atmosphere.

 1800-1875  ~John Dalton 1766-1844 **Sept. 6, 1766, England-July 27, 1844** __ **Dalton's Atomic Theory:** __ **1:** **All Matter is made of atoms. Atoms are indivisible (Can be split though as we later found out) and indestructible. 2: All atoms of a given element are identical in mass and properties. 3. Compounds are formed by a combination of two or more different kinds of atoms. 4. A chemical reaction is a rearrangement of atoms.**

~ **Amedeo Avogadro** 1776-1856

He was an Italian physicist,In 1811 Avogadro proposed that equal volumes of gas at the same temperature and pressure contain the same number of molecules. Avogadro himself coined the word "molecule" to mean the smallest part of a compound. On the basis of his law Avogadro became the first to show that water is H2O -- that is, composed of molecules of two atoms of hydrogen and one of oxygen. The related concept, called Avogadro's number, is that when the mass of a compound in grams is equal to the molecular weight, the total number of molecules is always the same, equal to 1 mole. (http://www.answers.com/Amedeo Avogadro)

~Wilhelm Roentgen He was born on March 27, 1845 and died on February 10, 1923. Rontgen was a very successful German physicist known for his expertise in X-Rays and winning the Nobel Prize in Physics in 1901. Roentgen was the first to dicover the x-ray while doing extensive studies with the "Crookes Tube". It was a glass tube that used a vacuum and a positively electrical charge on one side, leading to the discovery that the small prticles were attracted to the metal on the side away from the charge. This showed that the particles had to have a negative charge because they pushed away from the positive source. The "Crookes Tube" lead to many discoveries including Roentgen's x-ray discovery, while using the tube to study cathode rays being emitted. After placing photogenic paper near the tube he found it was discolored after a few minutes. Then he noticed that when a solid object was placed between the paper and the tube it left a shadow of the object between the two. The atoms did not go throught the object but ones that did discolored the paper. This was Roentgen's first discovery of the x-ray.

~ Henri Becquerel 1896 Becquerel was born December 15 1852 and died on A ugust 25 1908. He was a French physicist and chemist known for his studies in radioactivity. Henri studied the effects of X-Rays on photographic film, while studying this he discovered the fact that there are chemicals that spontaneously decompose and give off penetrating rays.

~J.J Thomson 1897



Thomson was born December 18 1856 and died on August 30 1940. He was an English physicist who helped revolutionize the knowledge of atomic structure by his discovery of the electron in 1897. He received the Nobel Prize for physics in 1906 and was knighted in 1908. He was also known for his plumb pudding model of the atoms.

[[image:http://www.nisd.net/marshall/Departments/Sciencedept/Atomic%20Theory/Images/GoldFoilExpt.gif width="360" height="336"]]
Rutherford studied under J.J Thomson at the Cavendish Laboratory. His work set a very distinguished landmark in the history of atomic research as he developed Becquerel's discovery of Radioactivity into an exact and documented proof that atoms of the heavier elements, which were thought to be unchangeable, actually disintegrated into various forms of radiation. Rutherford was also the first to establish the theory of the nuclear atom and to carry out a transmutation reaction.(1919) Rutherford also worked side by side with Thomson and studied Thomson's plum pudding model. Rutherford performed an experiment to confirm the plum pudding model once again but instead he proved it wrong. In his experiment Rutherford directed positively charged particles at a thin sheet of gold foil. The particles were to act as probes off the gold atom structure. If these gold atoms were like plum pudding, with their mass and volume spread throughout the entire atom, the super fast probes should pass directly throught the piece of gold foil with minimum deflection. In his experiment most of the particles passed directly through the foil, some were deflected and some bounced back. In conclusion Rutherford concluded matter has large regions of empty space dotted with small regions of very dense matter.



Neils Bohr- 7 October 1885-18 November 1962 Bohr was a made great strides in the fields of Quantum Mechanics and Quantum Physics. His research went against Einstein's theory that everything had an order to it. He with the help of his colleges theorized that atoms were made up of smaller particles and that atomic and subatomic levels were out of control. This idea seemed contravention at the time. (http://www.answers.com/topic/niels-bohr

~**James Chadwick** October 21,1891-//July 24, 1974//

Chadwick made a fundamental discovery in the domain of nuclear science: he proved the existence of neutrons - elementary particles devoid of any electrical charge. In contrast with the alpha rays which are charged, and therefore repelled by the considerable electrical forces present in the nuclei of heavy atoms, this new tool in atomic disintegration need not overcome any electric barrier and is capable of penetrating and splitting the nuclei of even the heaviest elements. Chadwick in this way prepared the way towards the fission of uranium 235 and towards the creation of the atomic bomb. For this epoch-making discovery he was awarded the Hughes Medal of the Royal Society in 1932, and the Nobel Prize for Physics in 1935

(http://nobelprize.org/nobel_prizes/physics/laureates/1935/chadwick-bio.html)

~Marie Curie 1867-1934 Marie Curie is best known for her discovery of radioactivity, the process of isolating radioactive isotopes. Marie suggested that her discovery in radioactivity could be used to battle cancer. She also was the proud discoverer of two elements that she name polonium and radium. She took tons of ore and separated the the radioactive substance out of it. The result was very small compared to the amount of ore. Curie also discovered that radioactive atoms have the ability to treat and kill cancer cancerous cells. She was awarded the Nobel Prize in physics. Unfortunately her constant exposure to her radioactive experiments eventually gave her cancer and killed her, she died in 1934.

(http://www.answers.com/topic/marie-curie)

~Werner Heisenberg 1901-1976 1925: Heisenberg developed the first version of quantum mechanics, a method of calculating quantum atomic particles using Matrices. 1927: Heisenberg came up with the uncertainty principle, a foundation of quantum theory. (http://www.answers.com/Werner%20Heisenberg)

Robert Millikan Robert was most well known for his discovery of the electric charge of the electron. He eventually came up with the photoelectric effect theory. In 1923 he began a major study of cosmic rays, first identified in 1912 by Victor Hess, which was to occupy him for the rest of his career. His first aim was to show that they did not originate in our atmosphere. To do this he devised an [|ingenious] set of observations made at two lakes in the San Bernadino mountains of southern California. The lakes were many miles apart and differed by 6700 feet (2042 m) in altitude. The difference in altitude would have the same effect on intensity of cosmic rays as six feet of water. He found that the intensity of ionization produced by the incoming cosmic rays in the lower lake was the same as the intensity six feet deeper in the higher lake. (http://www.answers.com/Robert%20Millikan)

Erwin Schrodinger He became the first to recognized for the theory of wave mechanics. But is best known for his Schrödinger's Cat paradox. In this experiment where he describes waves in the form of probablility as opposed to observable results.
 * (http://www.answers.com/%20Erwin%20Schrodinger)

As you can see, the top left atom diagram is Dalton's idea of an atom, this idea stayed the same until Thompson theorized that there was more to the atom then just one part, his model included negatively charged particles. Rutherford's idea added on this plumb pudding idea, in which there was a small positively charged center and the negatively charged particles surrounded it. Bohr took this idea and basically said that the electrons were in orbits around the nucleus. Today's model is the last one, the electrons aren't in a fixed location, however they jump from cloud to cloud when excited.