Fall.2008.MMA.Newell.McLaughlin.Timeline

Leucippus (fifth century BCE) Leucippus is said to have been born in Elea, Abdera or Miletus. Leucippus is named by most sources as the originator of the theory that the universe consists of two different elements, which he called ‘the full’ or ‘solid,’ and ‘the empty’ or ‘void. The extent of Leucippus' contribution to the developed atomist theory is unknown. Most reports refer to the views of Democritus alone, or to both atomists together; some seem even to have denied that there was a philosopher Leucippus.

http://plato.stanford.edu/entries/leucippus/

Democritus was born at Abdera, about 460 BCE, although according to some 490. Democritus expanded the atomic theory of Leucippus. He believed that it was impossible to divide things. He argued the eternity of existing nature, of void space, and of motion. He supposed the atoms, which are originally similar, to be impenetrable and have a density proportionate to their volume. Democritus ascribed the causes of things to necessity, and also to chance or absence of purpose.

http://plato.stanford.edu/entries/democritus/

Aristotle was born in 384 BCE. at Stagirus, a Greek colony and seaport on the coast of Thrace. Aristotle declares the existence of only four elements: fire, air, water and earth. All matter is made up of these four elements and matter had four properties: hot, cold, dry and wet.

http://www.columbia.edu/itc/chemistry/chem-c2507/navbar/chemhist.html

John Dalton (1766–1844) was born into a modest Quaker family in Cumberland, England, and earned his living for most of his life as a teacher and public lecturer, beginning in his village school at the age of 12. Dalton arrived at his view of atomism by studying meteorology. He was very interested in the study: he kept daily weather records from 1787 until his death. He proceeded to calculate atomic weights from percentage compositions of compounds, using an arbitrary system to determine the likely atomic structure of each compound.

http://www.chemheritage.org/classroom/chemach/periodic/dalton.html Joseph Priestley (1733–1804) Priestley was educated to be a minister in the churches that dissented from the Church of England, and he spent most of his life as a preacher or teacher. He was best remembered for his discovery of oxygen, and was ceremoniously welcomed to the United States in 1794 as a leading contemporary thinker and friend of the new republic. Priestley's first scientific work, The History of Electricity (1767), was encouraged by Benjamin Franklin, whom he had met in London. In preparing the publication Priestley began to perform experiments—at first merely to reproduce those he read about in the literature but later to answer questions of his own. In the 1770s he began his most famous scientific research on the nature and properties of gases. At that time he was living next to a brewery, which provided him an ample supply of carbon dioxide.

http://www.chemheritage.org/classroom/chemach/forerunners/priestley.html

Antoine-Laurent Lavoisier (1743–1794) completed a law degree in accordance with family wishes. His real interest, however, was in science, which he pursued with passion while leading a full public life. On the basis of his earliest scientific work, mostly in geology, he was elected in 1768—at the early age of 25—to the Academy of Sciences, France's most elite scientific society. In 1775 Lavoisier was appointed a commissioner of the Royal Gunpowder and Saltpeter Administration and took up residence in the Paris Arsenal. There he created a fine laboratory, which attracted young chemists from all over Europe to learn about the "Chemical Revolution" then in progress. He meanwhile succeeded in producing better gunpowder by increasing the supply and ensuring the purity of the constituents—saltpeter (potassium nitrate), sulfur, and charcoal—as well as by improving the methods of granulating the powder.

http://www.chemheritage.org/classroom/chemach/forerunners/lavoisier.html

Friedrich Wöhler (1800–1882) Wöhler, driven by a need to obtain the finest education in chemistry, went to Sweden to study with Jöns Jakob Berzelius after taking his medical degree at the University of Heidelberg. Even after returning to Germany, Wöhler remained Berzelius's loyal supporter for many years, translating several editions of Berzelius's textbook into German as well as his annual reports on chemical progress. The University of Göttingen, where Wöhler taught for nearly 50 years, became an international mecca for chemistry graduate students. Perhaps the most famous creation of an isomeric compound was Wöhler's accidental synthesis of urea in 1828, when he was attempting to prepare ammonium cyanate (which he later succeeded in preparing by allowing the crystals to form at room temperature instead of by evaporating the solution).

http://www.chemheritage.org/classroom/chemach/chemsynthesis/liebig-wohler.html

Friedrich August Kekule von Stradonitz (7 September 1829 – 13 July 1896) was a German organic chemist. One of the most prominent chemists in Europe from the 1850s until his death He was known especially in the theoretical realm, he was the principal founder of the theory of chemical structure. This theory proceeds from the idea of atomic valence, especially the tetravalence of carbon (which Kekulé announced late in 1857) and the ability of carbon atoms to link to each other (announced in a paper published in May 1858), to the determination of the bonding order of all of the atoms in a molecule. Kekulé's most famous work was on the structure of benzene. In 1865 Kekulé published a paper in French (for he was then still in Francophone Belgium) suggesting that the structure contained a six-membered ring of carbon atoms with alternating single and double bonds.

http://en.wikipedia.org/wiki/Friedrich_August_Kekulé_von_Stradonitz

Stanislao Cannizzaro (1826–1910) He was born in Palermo, Sicily, where his father was a magistrate and the minister of police, and he later attended medical school there, which kindled an interest in chemistry. Despite his family's connections to the royal court in Naples, he joined the antimonarchical 1848 revolution in Sicily. When it failed, he fled to Paris, where he resumed his chemical studies. In 1858, two years after Amedeo Avogadro's death, his fellow Italian Stanislao Cannizzaro outlined a course in theoretical chemistry for students at the University of Genoa—where he taught without the benefit of a laboratory. He used Avogadro's hypothesis as a pathway out of the confusion rampant among chemists about atomic weights and the fundamental structure of chemical compounds. After returning to Italy, he held academic appointments in Alessandria, where he worked out the "Cannizzaro reaction"—the self-oxidation and self-reduction of aldehydes—and Genoa, where he expounded Avogadro's hypothesis.

http://www.chemheritage.org/classroom/chemach/periodic/cannizzaro.html

Theodore William Richards (1868–1928), the first American to be awarded the Nobel Prize in chemistry, received it for his accurate determinations of atomic weights—25 in all, including those used to determine virtually all other atomic weights. Richards was educated at home by his mother, a Quaker author and poet, and his father, a noted painter of seascapes, until he went to Haverford College at the age of 14. He proceeded to Harvard, where he earned a doctorate in chemistry by the time he was 20. He remained there as an important researcher and teacher, except for two sojourns in Europe—first on a prize fellowship and, much later, to learn about the latest developments in electrochemistry and thermodynamics to pass on to his students.His work, which he began publishing in 1887, corrected earlier studies done in the 1860s by Jean Servais Stas. Among other contributions, Richards provided the experimental verification of the isotope concept, showing that lead from different sources has different atomic weights.

http://www.chemheritage.org/classroom/chemach/periodic/richards.html

Glenn Theodore Seaborg (1912–1999) was involved in identifying nine transuranium elements (94 through 102), and he served as chairman of the U.S. Atomic Energy Commission (AEC) from 1961 to 1971. In 1951 he shared the Nobel Prize in chemistry with the physicist Edwin M. McMillan. Born in Michigan, Seaborg earned his bachelor's degree at the University of California at Los Angeles and his doctorate in chemistry from the University of California at Berkeley. He then served as research assistant to Gilbert Newton Lewis and eventually became chancellor of the university. He worked away from Berkeley during two significant periods: once to participate in the Manhattan Project at the University of Chicago from 1942 to 1946 and then again to chair the AEC—from which he returned to Berkeley. Seaborg then joined the Manhattan Project to work on the plan for producing sufficient plutonium 239 for a bomb—the one that was dropped on Nagasaki. Even before the war ended, he turned his attention to the production of further transuranium elements, developing the actinide transition series in the periodic table.

http://www.chemheritage.org/classroom/chemach/atomic/seaborg.html

Linus Carl Pauling (1901–1994) Born in Portland, Oregon, Pauling received his bachelor's degree from Oregon State University and his Ph.D. in chemistry from the California Institute of Technology—despite the economic difficulties experienced by his family. After a short stay at the Center for the Study of Democratic Institutions in Santa Barbara, California, he resumed his laboratory research at the University of California at San Diego, from which he moved on to Stanford University, and finally to the Linus Pauling Institute of Science and Medicine in Palo Alto. He earned the Nobel Prize in chemistry in 1954. Among his accomplishments, he determined crystal structures by X-ray crystallography and the structures of gas molecules by electron diffraction. He studied the magnetic properties of substances, including hemoglobin, which helped him developed the molecular cause of sickle-cell anemia. He developed an electronegativity scale to assign to atoms involved in covalent and ionic bonding, and he formulated the concept of "resonance" to talk about the state of a chemical system where none of the classical structural formulas is entirely consistent with observed properties. He extended the theory of covalent bonds to include metals and intermetallic compounds. He proposed helical structures for proteins based on the coplanarity of the atoms in the peptide bond. But Pauling is perhaps best known to the public for championing the use of vitamin C to maintain and restore health.

http://www.chemheritage.org/classroom/chemach/chemsynthesis/pauling.html

Wilhelm Conrad Roentgen

(27 March 1845 – 10 February 1923)

Wilhelm was born in Prussia. He was educated at a young age, but had trouble finding a school to attend because he was expelled from one institution. He finally entered the Federal Polytechnic Institute in Zurich. He had a successful career at this institute and graduated with a Ph. D. in mechanical engineering. Wilhelm became a lecturer and then a professor at numerous universities. He discovered the X-Ray in 1895. The first picture ever taken with an X-Ray was of his wife’s hand.

￼￼ http://www.historicalprintshop.com/web_pages/M/medicine/medicine.illustration/med.illustration.k_r/25914.roentgen.jpg http://www.encyclopedia.com/doc/1E1-X-Rontgen.html

Scientists 1900-1915

Henri Becquerel

(December 15, 1852 - August 25, 1908)

Henri Becquerel was born in Paris. Henri came from a long line of scientists and scholars. Becquerel's earliest work was concerned with the plane polarization of light, with the phenomenon of phosphorescence and with the absorption of light by crystals. He also worked on the subject of terrestrial magnetism. In 1896, his previous work was overshadowed by his discovery of the phenomenon of natural radioactivity. Becquerel decided to investigate whether there was any connection between X-rays and naturally occurring phosphorescence. He had inherited from his father a supply of uranium salts, which phosphoresce on exposure to light. When the salts were placed near to a photographic plate covered with opaque paper, the plate was discovered to be fogged. The phenomenon was found to be common to all the uranium salts studied and was concluded to be a property of the uranium atom. Later, Becquerel showed that the rays emitted by uranium caused gases to ionize and that they differed from X-rays in that they could be deflected by electric or magnetic fields. For his discovery of spontaneous radioactivity Becquerel was awarded half of the Nobel Prize for Physics in 1903.

￼

http://nobelprize.org/nobel_prizes/physics/laureates/1903/becquerel-bio.html

Ernest Rutherford

(August 30, 1871 - October 19, 1937)

Ernest Rutherford was born in Nelson, New Zealand. He completed a degree at the University of New Zealand. Ernest Rutherford was responsible for a series of discoveries in the fields of radioactivity and nuclear physics. He discovered alpha and beta rays, set forth the laws of radioactive decay, and identified alpha particles as helium nuclei. Most important, he postulated the nuclear structure of the atom: experiments done in Rutherford's laboratory showed that when alpha particles are fired into gas atoms, a few are violently deflected, which implies a dense, positively charged central region containing most of the atomic mass. He received the Nobel Prize in chemistry for 1908.

￼

http://www.chemheritage.org/classroom/chemach/atomic/rutherford.html

Joseph John Thomson

(December 18, 1856 - August 30, 1940)

JJ Thompson was born near Manchester, England. His father died when he was only sixteen. The young Thomson attended Owens College in Manchester, where his professor of mathematics encouraged him to apply for a scholarship at Trinity College, one of the most prestigious of the colleges at Cambridge University. Thomson won the scholarship, and in 1880 finished second in his class (behind Joseph Larmor) in the grueling graduation examination in mathematics. Trinity gave him a fellowship and he stayed on there, trying to craft mathematical models that would reveal the nature of atoms and electromagnetic forces. ￼ http://nobelprize.org/nobel_prizes/physics/laureates/1906/thomson-bio.html http://www.aip.org/history/electron/jjthomson.htm



Marie Sklodowska Curie discovered the mysterious element radium. She was born November 7,1867 in Warsaw, Poland. Both her parents were teachers so she knew the importance of a good education. She graduated high school at 15 with high honors and after suffering from depression for a year she attended a secret college. This was because women were not allow to attend the University of Warsaw.Marie began looking for a research topic that would earn her a doctorate in science. No woman in the world had yet completed that degree. Trying out various chemicals, Marie found that compounds that contained an uncommon element, thorium, also gave off rays. To describe the behavior of these two elements, Marie made up the term “radioactivity.” In 1911, Curie became the first person to win a second Nobel Peace Prize. Curie used X-ray machines to help soldiers during World War 1. On July 4, 1934, Marie Curie died of aplastic anemia, a blood disease that often results from getting too much radiation.

http://nobelprize.org/nobel_prizes/physics/laureates/1903/marie-curie-bio.html

Scientists 1915 - 1950

Neils Bohr

(October 7, 1885 - November 18, 1962)

Bohr was born in Copenhagen, Denmark. Bohr made numerous contributions to our understanding of the structure of properties of atoms. He won the 1922 Nobel Prize for physics, chiefly for his work on atomic structure. In 1913, Bohr published a theory about the structure of the atom based on an earlier theory of Rutherford's. Rutherford had shown that the atom consisted of a positively charged nucleus, with negatively charged electrons in orbit around it. Bohr expanded upon this theory by proposing that electrons travel only in certain successively larger orbits. He suggested that the outer orbits could hold more electrons than the inner ones, and that these outer orbits determine the atom's chemical properties.

￼ http://nobelprize.org/nobel_prizes/physics/laureates/1922/bohr-bio.html http://www.lucidcafe.com/library/95oct/nbohr.html

James Chadwick

(October 20, 1891 - July 24, 1974)

James Chadwick was born in Cheshire, England. He graduated from Manchester University's Honors School of Physics in 1911 and spent the next two years working on various radioactivity problems in the Physical Laboratory in Manchester, earning a M.Sc. degree in 1913 as well as the 1851 Exhibition Scholarship, which allowed him to continue his research and move to Berlin to work with Professor Hans Geiger. In 1932, Chadwick proved the existence of neutrons, preparing the way towards the fission of Uranium 235 and the creation of the atomic bomb. He was awarded the Hughes Medal of the Royal Society in 1932, and subsequently the Nobel Prize for Physics in 1935. In that same year, he was elected to the Lyon Jones Chair of Physics at the University of Liverpool.

￼ http://nobelprize.org/nobel_prizes/physics/laureates/1935/chadwick-bio.html http://www.atomicarchive.com/Bios/Chadwick.shtml

Werner Heisenberg

(December 15, 1901 - February 1, 1976)

Werner was born in Würzburg. He was a German physicist and philosopher who discovered a way to formulate quantum mechanics in terms of matrices (1925). For that discovery, he was awarded the Nobel Prize for Physics for 1932. In 1927 he published his indeterminacy, or uncertainty, principle, upon which he built his philosophy and for which he is best known. He also made important contributions to the theories of the hydrodynamics of turbulence, the atomic nucleus, ferromagnetism, cosmic rays, and elementary particles, and he planned the first post-World War II German nuclear reactor, at Karlsruhe, then in West Germany.

￼

http://nobelprize.org/nobel_prizes/physics/laureates/1932/heisenberg-bio.html http://www.britannica.com/EBchecked/topic/259761/Werner-Heisenberg

Robert Millikan

(March 22, 1868 - December 19, 1953)

Robert Millikan was born in Morrison, Illinois in the U.S.A. After he graduated at Maquoketa High School he taught elementary physics for two years. He was appointed Fellow in Physics after receiving his mastership. Later he went on to receive his Ph.D. In 1923 he won the Nobel Prize for physics, for his study of the elementary electric charge and the photoelectric effect. Robert Millikan’s earliest major success was his "oil-drop" experiments, which measured an electrons charge and showed that the charge was a discrete constant rather than a statistical average. He later studied cosmic rays, which he names, physical and electric constants and X rays. He verifies Einstein’s photoelectric effect and made the first direct photoelectric determination of Planck’s constant. He also studies Brownian movement in gasses and put an end to the opposition against the kinetic and atomic theories of matter.

￼

http://nobelprize.org/nobel_prizes/physics/laureates/1923/millikan-bio.html http://library.thinkquest.org/28582/bio/millikan.htm

Erwin Schrodinger

(August 12, 1887 - January 4, 1961)

Schrodinger was born in Vienna. He published four papers in 1926 that laid the foundation of the wave-mechanics approach to quantum theory and set forth his now-famous wave equation. Schrodinger earned a doctorate at the University of Vienna in 1910. He succeeded in 1927 Max Planck in the chair of theoretical physics at the University of Berlin but left Germany in 1933 because of Nazi threats--the same year he shared the Nobel Prize for physics with Paul Dirac for his contributions to atomic theory. In 1939 he joined the newly formed Institute for Advanced Studies in Dublin. There he continued his studies of the application and statistical interpretation of wave mechanics, the mathematical character of the new statistics, and the relationship of these statistics to statistical thermodynamics. He also worked on problems of general relativity and cosmology and on a unified field theory. Late in his life Schrodinger studied the foundations of physics and their implications for philosophy

￼

http://nobelprize.org/nobel_prizes/physics/laureates/1933/schrodinger-bio.html

Information was found on http://www.aip.org/history/curie/brief/index.html



Electron Cloud Model The model evolved from the earlier Bohr model, which likened an electron orbiting an atomic nucleus to a planet orbiting the sun. The electron cloud formulation better describes many observed phenomena, including the double slit experiment, the periodic table and chemical bonding, and atomic interactions with light. Although lacking in certain details, the intuitive model roughly predicts the experimentally observed wave-particle duality, in that electron behavior is described as a delocalized wavelike object, yet compact enough to be considered a particle on certain length-scales. Experimental evidence suggests that the probability density is not just a theoretical model for the uncertainty in the location of the electron, but rather that it reflects the actual state of the electron. This carries an enormous philosophical implication, indicating that point-like particles do not actually exist, and that the universe's evolution may be fundamentally uncertain. The fundamental source of quantum uncertainty is an unsolved problem in physics. http://en.wikipedia.org/wiki/Electron_cloud

Planetary Model By 1911 the components of the atom had been discovered. The atom consisted of subatomic particles called protons and electrons. However, it was not clear how these protons and electrons were arranged within the atom. J.J. Thomson suggested the"plum pudding" model. In this model the electrons and protons are uniformly mixed throughout the atom. Rutherford tested Thomson's hypothesis by devising his "gold foil" experiment. Rutherford reasoned that if Thomson's model was correct then the mass of the atom was spread out throughout the atom. Then, if he shot high velocity alpha particles (helium nuclei) at an atom then there would be very little to deflect the alpha particles. He decided to test this with a thin film of gold atoms. As expected, most alpha particles went right through the gold foil but to his amazement a few alpha particles rebounded almost directly backwards. http://www.iun.edu/~cpanhd/C101webnotes/modern-atomic-theory/rutherford-model.html

Neil Bohr’s Model In atomic physics, the Bohr model created by Niels Bohr depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus—similar in structure to the solar system, but with electrostatic forces providing attraction, rather than gravity. This was an improvement on the earlier cubic model (1902), the plum-pudding model (1904), the Saturnian model (1904), and the Rutherford model (1911). Since the Bohr model is a quantum physics-based modification of the Rutherford model, many sources combine the two, referring to the Rutherford-Bohr model. http://en.wikipedia.org/wiki/Bohr_model

Plum Pudding Model The plum pudding model of the atom by J.J. Thomson, who discovered the electron in 1897, was proposed in 1904 before the discovery of the atomic nucleus. In this model, the atom is composed of electrons (which Thomson still called "corpuscles," though G.J. Stoney had proposed that atoms of electricity be called electrons in 1894) [1], surrounded by a soup of positive charge to balance the electron's negative charge, like negatively-charged "plums" surrounded by positively-charged "pudding". The electrons (as we know them today) were thought to be positioned throughout the atom, but with many structures possible for positioning multiple electrons, particularly rotating rings of electrons (see below). Instead of a soup, the atom was also sometimes said to have had a cloud of positive charge. http://en.wikipedia.org/wiki/Plum_pudding_model