Fall.2008.MMA.Wheelock.Timeline


 * __Pre 450 AD__**
 * Thales**-Around 600 BC Thales of Miletus discovered that after rubbing a piece of amber with fur it would attract other light objects. He suggested that this force came from inside the amber but did not completely develope his idea and connect it with the atom.


 * Democritus(**460BC to 370BC)-It wasn't until 460 BC that the Greek philosopher came up with the idea of atoms. He said that there was only so many times that something could be broken down into smaller pieces than the previous one. It had to end at some point with the smallest thing you could get, the atom. He was the founder of the atomic hypothesis. He thought that everything was formed up of atoms like the objects itself, such as all trees were lots of small trees put together.


 * Leucippus(**480BC to 420BC)-He was a 5th century Greek philosopher. He is not very well known and has very little work attributed to him because of Democritus. There are no writings that can be credited to him either. Aristotle though credits him with the invention of atomism. Epicuros denies the fact that there ever was such a person alive named Leucippus.


 * __1700 to 1800__**


 * Antoine Lavoisier**(1743-1794)-He was a French nobleman who studied chemistry, biology, and economics. He discovered that even when matter changes its form it will always have the same mass as when it started. This is the law of conservation of mass. In 1787 he invented the system of chemical nomenclature, which is still used today. During the French Revolution he was beheaded.

//**
 * Charles Coulomb**-(1736-1806)-Charles is best known for Coulomb's Law. He was born into a wealthy French family where he went on to study mathmatics and become a physicist. He then went into the military where he spent his time mapping the British coast and constructing Fort Bourbon. In 1789 when the revolution broke out in France he was stationed in Paris. He stepped down from his position and went to live on his family's estate. In 1784 Coulomb formulated his law. It stated that the force between two electrical charges is proportional to to the product of the charges, one of the main forces in an atomic reaction. **//F=q1q2/r2


 * __1800-1875__**

John Dalton(1766-1844)-Dalton was an English chemist, physicist, and meteorologist. He is best known though for his work with the atom. Dalton formed an atomic theory. 1.All matter is made of atoms. Atoms are invisible and indestructible. 2.All atoms of a certain element have the same mass and properties. 3.Compounds are formed by a combination of two or more different kinds of atoms. John Dalton also developed the first table of elements and was amazingly close to what the table is today. It was pretty amazing considering the limited technology he had to work with and the fact that no one had attempted to make one before this. Dalton came to the realize that atoms determine the composition of an object, not the properties. Small, spherical, invisible model-Dalton theorized that the atom was the smallest piece of matter. He described these as small, invisible, solid spheres with density. He also said that all elements had a certain count of atoms and if it was changed the slightest bit the element would form a new one.


 * William Crookes**(1832-1919)-William Crookes was born in England to a tailor, but started his scientific career when he was only 15. He was accepted to the Royal College of Chemistry. In 1861 he discovered an unknown element with a bright green emission line and named it thallium. He discovered that as the pressure is lowered, the negative electrode appears to emit rays. These cathode rays were really a stream of free electrons. He invented the Crooke's tube and Crooke's radiometer.


 * Amedeo Avogadro**(1776-1856)-Amedeo was born to a wealthy Italian family is Turin. At 20 years old he graduated in ecclesiastical law and began to practice. He soon dedicated himself to the study of physics and mathematics and in 1809 started teaching. In 1811 he came out with his hypothesis in "An Essay on Determining the Relative Masses of the Elemental Molecules of Bodies and Proportions by Which They Enter These Combinations." In it he said that "equal volumes of all gases at the same temperatureand pressure contain the same amount of molecules." One of his most important contributions was differntiating between molecules and atoms. He said "gases are composed of molecules and these molecules are composed of atoms." He believed that there were three types of molecules. In honor of his contribution to the theory of molarity the number of molecules in one mole was given the name Avogadro's Number.




 * __1875-1900__**


 * Henri Becquerel**(1852-1908)-Becquerel was born into a family that would produce four generations of scientists. He studied science and engineering at Ecole Polytechnique. In 1892 he became the third person in his family to to occupy the physics chair at the Museum Natural d'Histoire Naturelle. He contributed to the research and discovery of radioactivity. In1896 when he was doing research on phosphorence in uramium salts he accidentally discovered radioactivity. He wrapped a flourescent substance in photographic plates and black material in preparation for bright sunlight, but instead when he went to perform the experiment he found the plates already exposed. This led him to explore the emission of nuclear radiation. In 1903 he shared the Nobel Prize with the Curie's for his part in the discovery of spontaneous radioactivity.




 * Wilhelm Roentgen**(1845-1923)-He was a German physicist who produced and detected what are now known as x rays. Wilhelm was born in Prussia but soon moved with his family to the Netherlands. Here he attended many different universities, even being expelled from one for not telling on another student who drew a picture of a teacher on the wall. He had family in Iowa and had purchased transatlantic tickets, but these plans were put on hold with the outbreak of World War 1 and he stayed in Munich for the rest of his life. In 1895 he was investigating the external effects of vacuum tubes on when an electrical charge was passed through them. He was using one of Lenard's tubes in which he placed a thin aluminum window to allow the cathode rays to leave the tube, but there was a cardboard covering to protect the aluminum. He observed that the cathode rays caused a flourescent effect on a piece of cardboard that was painted with barium platinocyanide. He would go on using more powerful vacuums and using the first xray on a human when he took a picture of his wife's hand.


 * Marie Curie**(1867-1934)-Marie was a Polish physicist and chemist. She was born in Warsaw and lived there until she was 24, where in 1891 she followed her older sister to Paris. Her she married Pierre Currie who would later help her with her research. Since she was a woman, Marie had to deal with issues in society. Woman were not looked at as equals at this time. Going on what Becquerel had discovered with uranium salts she used an electrometer to discover that uranium rays caused the air around a sample to conduct electricity. She had shown that the radiation was not the outcome of some interaction between molecules, but must have come from the atom itself. In 1989 she and her husband announced the discovery of a new element,polonium, and then a few months later discovered another element which they named, radium for its radioactivity.




 * __1900-1915__**


 * J.J Thomson**(1856-1940)-Thomson was born in England where he studied engineering at Owens College before moving on to Trinity College. When he was a professor of physics one of his students was Ernest Rutherford. Thomson's biggest contribution to the study of atoms was the Plum Pudding model which he constructed in 1904. In the model he shows that an atom is composed of electrons surrounded by positive charges to balance the electron's negative charge. He discovered the electron when he applying high voltage to gases at low pressure.




 * Robert Millikan**(1868-1953)-Robert was born in Iowa. He earned a Bachelor's in the classics and his doctorate in physics from Columbia University. In 1909 he and fellow professor Harvey Fletcher worked on an oil drop experiment in which they measured the charge of a single electron. Millikan took sole credit and went on to win the Noble Prize for Physics in 1923. Along with finding out the charge of an electron he also proved that the quanity was consistent for all electrons. This lead to the atomic structure of electricity.



In 1919 he became the first person to transmute one element into another when he converted nitrogen into oxygen.
 * Ernest Rutherford**(1871-1937)-He was born in New Zealand. He graduated Nelson College with math and physical science. He later moved to Canada to become the Chair of Physics at McGill University. In 1907 he carried out the Geiger-Marsden experiment which demonstrated the nuclear nature of atoms. The interpretation of this experiment led him to create the Rutherford model of the atom, which had a small positively charged nucleus orbited by electrons.

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf

Rutherford conducted this experiment with Hans Geiger. They had a thin sheet of gold foil surrounded by a strip of circular zinc sulfide. They then shot particles at the gold foil. They measured the deflection of these particles hitting the gold foil, they observed a small amount of particles deflected through angles larger than ninety degrees. Planetary model-In this model all of the electrons orbit around a small positively charged core. It was like the planets orbiting around the sun. All the positive charge and most of the mass would be concentrated in the nucleus of the atom, rather than spread throughout the atom.

Bohr-Rutherford model-Bohr came up with this model, which had electrons traveling around the nucleus of the atom. He also found out that the electron could move from a higher energy level to a lower one. Bohr's model is still used to explain many aspects of physical phenomena such as the appearance of spectra.
 * Neil Bohr**(1885-1962)-He was born in Denmark to a father who was a professor of physiology. He conducted experiments under JJ Thomson at Trinity College and studied under Rutherford at the University of Manchester. Bohr also worked on the Manhattan Project at the Los Alamos Laboratory. He was seen here as a knowledgeable consultant.


 * __1915-1950__

Werner Heisenberg**(1901-1976)-Werner was a German theoretical physicist who made contributions to quantum mechanics, nuclear physics, quantum field theory, and particle physics. After Hitler came to power in 1933 he was atttacked by the press and was investigated by the SS. Throughout the German nuclear energy porject he was one of nine principals heading up research and developement for the project. He was one of ten German scientists arrested near the end of WW2 under Operation Alsos and detained from 1945-1946. Once released he returned and moved into the British occupation zone. He discovered how to formulate quantum mechanics in terms of matrices and was awarded the Nobel Prize for it. In 1932 he concluded that charged particles bounce photons of light back and forth between them. This provides a way for for the electromagnetic forces to act between the particles.




 * James Chadwick**(1891-1974)-He was born in Chesire and later studied at the University of Manchester. He worked with Hans Greiger in 1913 at the Technical University of Berlin, he also worked with Rutherford. During WW1 he was detained in a POW camp where he set up a laboratory in the stables. After WW1 he returned to England to work with Rutherford. During WW2 he was also part of the Manhattan Project. In 1935 he won The Nobel Prize for his discovery of the neutron. In 1932 he had observed beryllium, when exposed to a bombardment of alpha particles released an unknown radiation that in turn ejected protons from the nuclei of other substances. He interpreted this radiation as being composed of particles of mass approximately equal to that of the proton, but without an electrical charge, neutrons.




 * Erwin Schrodinger**(1887-1961)-He was an Austrian theoretical physicist who worked on quantummechanics, including the Schrodinger equation. In 1924 he introduced the Schrodinger equation, it describes the behavior of matter that have a dual nature and in some situations act like waves. In 1944 he wrote "What is Life" to show how quantum physics can be used to explain the stability of the genetic structure.


 * __1950-Present__

Glen T Seaborg**(1912-1999)-An American chemist known for his work isolating and identifying transuranium elements. In 1951 McMillan and him shared the Nobel Prize for their dicovery of these elements. He had Seaborgium named after him, making him the only person to have an element named for them in their lifetime. He added elements 94-102 and 106. The elements he discovered were heavier than uranium.


 * George Sweig and Murray Gell-Mann-**These two physicists brought forth the idea of "quarks". Quark make up protons and neutrons. They are little bits of matter used like building blocks, and serve to explain some complex chemical equations.


 * Electron Cloud Model**-In this model electrons are not put in a fixed orbit, they are in certain areas aaround the nuclues of the atom. It doesn't say where the electrons are at any certain time, but where it could be.



http://www.broadeducation.com/htmlDemos/AbsorbChem/HistoryAtom/page.htm http://www.nobeliefs.com/atom.htm http://www.cerritos.edu/ladkins/a106/A%20Brief%20History%20of%20the%20Atom.htm http://content.answers.com/main/content/img/scitech/HSjohnda.jpg http://hi.fi.tripod.com/timeline/ __ http://www.britannica.com/ __