Fall.2008.MMA.Rowe.Timeline

Atomic History Timeline

Democritus Democritus was born in Abdera, the leading Greek city on the northern coast of the Aegean Sea, in the year 460 BC. Although the accient accounts of Democritus's career differ widely, they all agree that he lived to a ripe old age, 90 being the lowest figure. Therefore this would put his death around 370 BC. Democritus agreed that everything which is must be eternal, but denied that "the void" can be equated with nothing. This makes him the first thinker on record to argue the existence of an entirely empty "void". In order to explain the change around us from basic, unchangeable substance he created a theory that argued that there are various basic elements which always existed but can be rearranged into many different forms. Democritus' theory argued that atoms only had several properties, particularly size, shape, and (perhaps) weight; all other properties that we attribute to matter, such as color and taste, are but the result of complex interactions between the atoms in our bodies and the atoms of the matter that we are examining. Furthermore, he believed that the real properties of atoms determine the perceived properties of matter--for example, something that is solid is made of small, pointy atoms, while something that has water like properties is made of large, round atoms. Some types of matter are particularly solid because their atoms have hooks to attach to each other; some are oily because they are made of very fine, small atoms which can easily slip past each other. In Democritus' own words: // By convention there is sweet, by convention there is bitterness, by convention hot and cold, by convention color; but in reality there are only atoms and the void. //

http://www.bookrags.com/biography/democritus/ http://en.wikipedia.org/wiki/Democritus

Empedocles Empedocles lived from 490 BC to 430 BC. He was born in Acragas, Sicily . He also was a Greek pre-Socratic philosopher and a citizen of Agrigentum, a Greek colony in Sicily. Empedocles' philosophy is best known for being the origin of the cosmogenic theory of the four classical elements. It was Empedocles who established four ultimate elements which make all the structures in the world: fire, water, air, and earth. Empedocles called these four elements "roots", which, in typical fashion, he also identified with the mythical names of Zues, Hera, Nestis, and Aidoneus. Empedocles never used the term "element", which seems to have been first used by Plato. According to the different proportions in which these four indestructible and unchangeable elements are combined with each other the difference of the structure is produced. It is in the aggregation and segregation of elements thus arising, that Empedocles, like the atomists, found the real process which corresponds to what is popularly termed growth, increase or decrease. Nothing new comes or can come into being; the only change that can occur is a change in the juxtaposition of element with element. This theory of the four elements became the standard dogma for the next two thousand years. http://en.wikipedia.org/wiki/Empedocles

Aristotle Aristotle was born in 384 BC at Stagirus, a Greek colony and seaport on the coast of Thrace. His father Nichomachus was court physician to King Amyntas of Macedonia, and from this began Aristotle's long association with the Macedonian Court, which considerably influenced his life. Atristole died in 322 BC when he complained of a stomach illness. It was Aristotle, along with Empedocles, who developed the theory of the four elements: water, earth, air, and fire.

http://www.iep.utm.edu/a/aristotl.htm http://www.webwinds.com/thalassa/elemental.htm

Joseph Priestly Joseph Priestley (1733–1804), best remembered for his discovery of oxygen, was ceremoniously welcomed to the United States in 1794 as a leading contemporary thinker and friend of the new republic. Then 61, he was known to Americans at least as well for his prodigious political and theological writings as for his scientific contributions. Priestley was educated to be a minister in the churches that dissented from the Church of England, and he spent most of his life employed as a preacher or teacher. He gradually came to question the divinity of Jesus, while accepting much else of Christianity—in the process becoming an early Unitarian. 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 reported 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. His first //chemical// publication was a description of how to carbonate water, in imitation of some naturally occurring bubbly mineral waters. Inspired by Stephen Hales's //Vegetable Staticks// (first edition, 1727), which described the pneumatic trough for gathering gases over water, Priestley began examining //all// the "airs" that might be released from different substances. Many, following Aristotle's teachings, still believed there was only one "air." By clever design of apparatus and careful manipulation, Priestley isolated and characterized eight gases, including oxygen—a record not equaled before or since. In addition, he contributed to the understanding of photosynthesis and respiration. http://www.chemheritage.org/classroom/chemach/forerunners/priestley.html

Antoine-Laurent Lavoisier

The son of a wealthy Parisian lawyer, 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 the same year he bought into the Ferme Générale, the private corporation that collected taxes for the Crown on a profit-and-loss basis. A few years later he married the daughter of another tax farmer, Marie-Anne Pierrette Paulze, who was not quite 14 at the time. Madame Lavoisier prepared herself to be her husband's scientific collaborator by learning English to translate the work of British chemists like Joeseph Priestly and by studying art and engraving to illustrate Antoine-Laurent's scientific experiments. He is also known for the creation of the law of conservation of mass, which states that matter cannot be created, nor destroyed. http://www.chemheritage.org/classroom/chemach/forerunners/lavoisier.html

John Dalton 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. After teaching 10 years at a Quaker boarding school in Kendal, he moved on to a teaching position in the burgeoning city of Manchester. There he joined the Manchester Literary and Philosophical Society, which provided him with a stimulating intellectual environment and laboratory facilities. The first paper he delivered before the society was on color blindness, which afflicted him and is sometimes still called "Daltonism." He proceeded to calculate atomic weights from percentage compositions of compounds, using an arbitrary system to determine the likely atomic structure of each compound. If there are two elements that can combine, their combinations will occur in a set sequence. The first compound will have one atom of A and one of B; the next, one atom of A and two atoms of B; the next, two atoms of A and one of B; and so on. Hence, water is HO. Dalton also came to believe that the particles in different gases had different volumes and surrounds of caloric, thus explaining why a mixture of gases—as in the atmosphere—would not simply layer out but was kept in constant motion. Dalton consolidated his theories in his //New System of Chemical Philosophy// (1808–1827). http://www.chemheritage.org/classroom/chemach/periodic/dalton.html

James Clerk Maxwell The Scottish physicist James Clerk Maxwell, b. Nov. 13, 1831, d. Nov. 5, 1879, did revolutionary work in electromagnetism and the kinetic theory of gases. After graduating (1854) with a degree in mathematics from Trinity College, Cambridge, he held professorships at Marischal College in Aberdeen (1856) and King's College in London (1860) and became the first Cavendish Professor of Physics at Cambridge in 1871. Maxwell's most important achievement was his extension and mathematical formulation of Michael Faraday's theories of electricity and magnetic lines of force. In his research, conducted between 1864 and 1873, Maxwell showed that a few relatively simple mathematical equations could express the behavior of electric and magnetic fields and their interrelated nature; that is, an oscillating electric charge produces an electromagnetic field. These four partial differential equations first appeared in fully developed form in Electricity and Magnetism (1873). Since known as Maxwell's equations they are one of the great achievements of 19th-century physics. Maxwell also calculated that the speed of propagation of an electromagnetic field is approximately that of the speed of light. He proposed that the phenomenon of light is therefore an electromagnetic phenomenon. Because charges can oscillate with any frequency, Maxwell concluded that visible light forms only a small part of the entire spectrum of possible electromagnetic radiation. Maxwell used the later-abandoned concept of the ether to explain that electromagnetic radiation did not involve action at a distance. He proposed that electromagnetic-radiation waves were carried by the ether and that magnetic lines of force were disturbances of the ether. Heinrich Hertz discovered such waves in 1888. http://www.phy.hr/~dpaar/fizicari/xmaxwell.html

GJ Stoney Dr. Stoney was born in Ireland in February, 1826 (1826-1911). He was the eldest son of George Stoney, of Oakley Park, King's County; his mother was Ann, daughter of Bindon Blood, of Cranagher and Rockforrest, county Clare. His sister married the Rev. William Fitzgerald, afterwards Bishop of Cork and subsequently of Killaloe. His only brother, Bindon Blood Stoney, F.R.S., was engineer to the Dublin Port and Docks Board. Stoney published seventy-five scientific papers in a variety of journals, making significant contributions to cosmic physics and to the theory of gases. He estimated the number of molecules in a cubic millimetre of gas, at room temperature and pressure, from data obtained from the kinetic theory of gases. Stoney's most important scientific work was the conception and calculation of the magnitude of the "atom of electricity". In 1891, he proposed the term 'electron' to describe the fundamental unit of electrical charge, and his contributions to research in this area laid the foundations for the eventual discovery of the particle by J.J. Thomson  in 1897. http://en.wikipedia.org/wiki/G._Johnstone_Stoney

Marie Curie Marie Sklodowska Curie (1867–1934) was the first person ever to receive two Nobel prizes: the first in 1903 in physics, shared with her husband Pierre and Henri Becquerel for the discovery of the phenomenon of radioactivity; and the second in 1911 in chemistry for the discovery of the radioactive elements polonium and radium. The daughter of impoverished Polish schoolteachers, Marie worked as a governess in Poland to support her older sister in Paris, whom she eventually joined. Already entranced with chemistry, Marie took advanced scientific degrees at the Sorbonne, where she met and married Pierre Curie, a physicist who had achieved fame for his work on the piezoelectric effect. For her thesis she chose to work in a field just opened up by Wilhelm Roentgen's discovery of X-rays and Becquerel's observation of the mysterious power of samples of uranium salts to expose photographic film. She soon convinced her husband to join in the endeavor of isolating the "radioactive" substance—a word she coined. In 1898, after laboriously isolating various substances by successive chemical reactions and crystallizations of the products, which they then tested for their ability to ionize air, the Curies announced the discovery of polonium, and then of radium salts weighing about 0.1 gram that had been derived from tons of uranium ore. http://www.chemheritage.org/classroom/chemach/atomic/curie.html

Wilhelm Roentgen Wilhelm Conrad Röntgen (27 March 1845 – 10 February 1923) was a <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">German physicist, who, on 8 November 1895, produced and detected <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">electromagnetic radiation in a <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">wavelength range today known as <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">x-rays or Röntgen rays, an achievement that earned him the first <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">Nobel Prize in Physics in 1901. Wilhelm Roentgen, Professor of Physics in Worzburg, Bavaria, was the first person to discover the possibility of using electromagnetic radiation to create what we now know as the x-ray. The image below is the first x-ray Roentgen ever created. It is an image of his wife's hand - you can see her wedding ring. <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">Roentgen was exploring the path of electrical rays passing from an induction coil through a partially evacuated glass tube. Although the tube was covered in black paper and the room was completely dark, he noticed that a screen covered in fluorescent material was illuminated by the rays. He later realised that a number of objects could be penetrated by these rays, and that the projected image of his own hand showed a contrast between the opaque bones and the translucent flesh. He later used a photographic plate instead of a screen, and an image was captured. In this way an extraordinary discovery had been made: that the internal structures of the body could be made visible without the necessity of surgery. <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;">http://en.wikipedia.org/wiki/Wilhelm_Conrad_R%C3%B6ntgen#Discovery_of_x-rays <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;">http://www.bl.uk/learning/cult/bodies/xray/roentgen.html

<span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;">JJ Thomson



In 1897 the physicist Joseph John (J. J.) Thomson (1856–1940) discovered the electron in a series of experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube—an area being investigated by numerous scientists at the time. Thomson interpreted the deflection of the rays by electrically charged plates and magnets as evidence of "bodies much smaller than atoms" that he calculated as having a very large value for the charge to mass ratio. Later he estimated the value of the charge itself. In 1904 he suggested a model of the atom as a sphere of positive matter in which electrons are positioned by electrostatic forces. His efforts to estimate the number of electrons in an atom from measurements of the scattering of light, X, beta, and gamma rays initiated the research trajectory along which his student <span style="color: windowtext; font-family: 'Times New Roman',Times,serif; font-size: 110%; text-decoration: none;">Ernest Rutherford moved. Thomson's last important experimental program focused on determining the nature of positively charged particles. Here his techniques led to the development of the mass spectroscope, an instrument perfected by his assistant, Francis Aston, for which Aston received the Nobel Prize in 1922. <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;">The plum pudding model of the <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">atom <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;"> by <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">J.J. Thomson <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;">, who discovered the <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">electron <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;"> in 1897, was proposed in 1904 before the discovery of the atomic nucleus. In this model, the atom is composed of electrons, surrounded by a soup of positive charge to balance the electron's negative charge, like negatively-charged " <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">plums <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;">" surrounded by positively-charged " <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">pudding <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;">". The electrons were thought to be positioned throughout the atom, but with many structures possible for positioning multiple electrons, particularly rotating rings of electrons. Instead of a soup, the atom was also sometimes said to have had a cloud of positive charge. <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">http://www.chemheritage.org/classroom/chemach/atomic/thomson.html <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;">http://en.wikipedia.org/wiki/Plum_pudding_model

Neils Bohr <span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">Neils Borh was born on October 7, 1885 in Copenhagen, Denmark. Neils received his diploma in physics from the University of Copenhagen in 1911. He then traveled to Manchester, England to study under British physicist Ernest Rutherford. In 1913 Bohr published a book about the structure of the atom which consisted of a positively charged nucleus, with negatively charged electrons orbiting around it. Bohr said that the outer orbits could hold more electrons that the inner ones, and that the outer orbits determine the atoms chemical properties. Bohr also said the way atoms give of radiation by saying that when an electron jumps from an outer orbit to an inner orbit, it gives of light.

<span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">Neils proposed that the electrons move in definite orbit around the nucleus, like the planets around the sun. These orbits, or energy levels, charged by the distance from the nucleus. He asserted That the electron in a hydrogen atom occupies one of an array of discrete orbits, each orbit being progressively farther from the nucleus and labeled with integer n=1, 2,....This integer is an example of a quantum number, which in general is an integer that labels the state of a system and which, though an appropriate formula, determines the values of a certain physical properties of the system. By matching the centrifugal effect of the electron's motion in it orbit to the electrostatic attraction of the nucleus for the electron, Bohr was able to find a relation between the energy of the electron and the quantum number of its orbit. The result he obtained was in almost perfect agreement with the observed values of the energy levels of a hydrogen atom that had previously been obtained by spectroscopic methods. Bohr's triumph was the first apparently successfully incorporation of a quantum theoretical ideas into the description of a mechanical system. The numerical success of the model has turned out to be considered, however, and Bohr's model is now as no more than a historically important http://www-outreach.phy.cam.ac.uk/camphy/nucleus/nucleus7_1.htm <span style="font-family: 'Calibri','sans-serif'; font-size: 11pt; line-height: 115%;">http://www.franklinlakes.k12.nj.us/famsweb/curriculum/science/SciProjects/ScienceprojectsPowers/%20Cory%20Abramson/CoryA.html

Ernest Rutherford <span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">Ernest Rutherford was born in Brightwater, New Zealand, into a family of pioneer stock who had emigrated from Britain less than 30 years earlier. Although he was a very good all-round scholar while at school, Rutherford showed no real bias to science. In 1890 he entered Canterbury College at Christchurch in New Zealand, where his scientific ability became apparent, and graduated with first-class degrees in both science and mathematics. <span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">Rutherford proposed that the atom contained a massive //nucleus// containing all of its positive charge, and that the much lighter electrons were outside this nucleus. The nucleus had a radius about ten thousand times smaller than the radius of the atom, only ten femtometers, or one hundred thousand billionth of a meter. <span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">Scattering at large angles occurred when the alpha particles came near to a nucleus. The reason that most alpha particles were not scattered at all was that they were passing through the relatively large 'gaps' between nuclei. <span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">Rutherford revised Thomson's 'plum pudding' model, showing how electrons could orbit a positively charged nucleus, like planets orbiting a sun. In 1915 Neils Bohr adapted Rutherford's model by saying that the orbits of the electrons were quantized, meaning that they could exist only at certain distances from the nucleus. <span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">The Rutherford model of the atom was soon superseded by the <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; text-decoration: none;">Bohr model <span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">, which used some of the early <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; text-decoration: none;">quantum mechanical <span style="font-family: 'Times New Roman','serif'; font-size: 12pt;"> results to give locational structure to the behavior of the orbiting electrons, confining them to certain circular (and later elliptical) planar orbits. In the Bohr model, expanding on the work of <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; text-decoration: none;">Henry Moseley <span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">, the central charge was identified as being directly connected with the <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; text-decoration: none;">atomic number <span style="font-family: 'Times New Roman','serif'; font-size: 12pt;"> (that is, the element's place on the periodic table). Since the Bohr model is an improvement on the Rutherford model in this and other ways, some sources combine the two, referring to the Bohr model as the Rutherford-Bohr model. However, even an atom with a core containing an atomic number of charges was the work of a number of men, including those mentioned, and also lesser known workers such as <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; text-decoration: none;">Antonius Van den Broek <span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">.

<span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">The Rutherford model was important because it essentially proposed the concept of the nucleus, although this word is not used in the paper. What Rutherford notes as the (probable) concomitant of this results, is a "concentrated central charge" in the atom: "Considering the evidence as a whole, it seems simplest to suppose that the atom contains a central charge distributed through a very small volume, and that the large single defluxions are due to the central charge as a whole, and not to its constituents." The central charge containing most of the atom's positive charge, invariably later become associated with a concrete structure, the atomic nucleus. <span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">After the Rutherford model and its confirmation in the experiments of <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; text-decoration: none;">Henry Moseley <span style="font-family: 'Times New Roman','serif'; font-size: 12pt;"> and its theoretical description in the <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; text-decoration: none;">Bohr model of the atom <span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">, the study of the atom branched into two separate fields, <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; text-decoration: none;">nuclear physics <span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">, which studies the nucleus of the atom, and <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; text-decoration: none;">atomic physics <span style="font-family: 'Times New Roman','serif'; font-size: 12pt;"> which studies atom's electronic structure. http://www.daviddarling.info/encyclopedia/R/Rutherford_Ernest.html http://en.wikipedia.org/wiki/Rutherford_model

Robert Millikan

<span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;">Robert Andrews Millikan (March 22, 1868 – December 19, 1953) was an <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">American <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;"> experimental <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">physicist <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;">, and <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">Nobel laureate <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;"> in physics for his measurement of the charge on the <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">electron <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;"> and for his work on the <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">photoelectric effect <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;">. He served as president of <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">Caltech <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;"> from 1921 to 1945. <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;">The <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">purpose <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;"> of <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">Robert Millikan <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;">and <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">Harvey Fletcher <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;">'s oil-drop experiment (1909) was to measure the <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">electric <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;"> charge of the <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">electron <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;">. They did this by carefully balancing the <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">gravitational <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;"> and <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">electric forces <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;"> on tiny charged droplets of <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">oil <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;"> suspended between two <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">metalelectrodes <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;">. Knowing the electric field, the charge on the oil droplet could be determined. Repeating the <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">experiment <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;"> for many droplets, they found that the values measured were always multiples of the same number. They interpreted this as the charge on a single electron: 1.602 × 10−19 <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">coulomb <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;"> ( <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">SIunit <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;"> for <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">electric charge <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;">). <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;">http://en.wikipedia.org/wiki/Oil-drop_experiment

Henri Becquerel <span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">Antoine Henri Becquerel (15 December 1852 – 25 August 1908) was a <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; text-decoration: none;">Frenchphysicist <span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">, <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; text-decoration: none;">Nobel laureate <span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">, and one of the discoverers of <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; text-decoration: none;">radioactivity <span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">. He won the 1903 <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; text-decoration: none;">Nobel Prize in Physics <span style="font-family: 'Times New Roman','serif'; font-size: 12pt;"> for discovering <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; text-decoration: none;">radioactivity <span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">French physics Professor Antoine Henri Becquerel discovered that uranium compounds produced rays that blacked photographic plates. Radioactivity or radioactive is the name of the property possessed by some elements of spontaneously emitting energetic particles and rays from their atomic nuclei. These emitted particles or rays are called radiation. An elemental material (such as uranium) that emits radiation is called radioactive material. Most, but not all, atomic nuclei are stable i.e. not radioactive. <span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">Radioactivity is a naturally occurring process that occurs when an unstable nucleus goes through a transformation, moving to a lower energy state accessible to the nucleus. The nuclei apart releasing energy in order to become stable. Nature always universally prefers to seek its lowest energy state. <span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">http://www.bccdc.org/content.php?item=67

<span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">Erwin Schrodinger <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;">Erwin Rudolf Josef Alexander Schrödinger (12 August 1887 – 4 January 1961) was an <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">Austriantheoretical physicist <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;"> who achieved fame for his contributions to <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">quantum mechanics <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;">, especially the <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">Schrödinger equation <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;">, for which he received the <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">Nobel Prize <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;"> in 1933. In 1935, after extensive correspondence with personal friend <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">Albert Einstein <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;">, he proposed the <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%; text-decoration: none;">Schrödinger's catthought experiment <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;">. <span style="font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 115%;">http://en.wikipedia.org/wiki/Erwin_Schr%C3%B6dinge

Werner Heisenberg Werner Heisenberg (5 December 1901 in Würzburg –1 February 1976 in Munich ) was a German theoretical physicist, best known for enunciating the Kramers-Heisenberg dispersion formula. He made important contributions to quantum mechanics, nuclear physics, quantum field theory , and particle physics. The Kramers-Heisenberg dispersion formula is an expression for the <span style="color: windowtext; font-family: 'Times New Roman',Times,serif; font-size: 110%; text-decoration: none;">cross section for <span style="color: windowtext; font-family: 'Times New Roman',Times,serif; font-size: 110%; text-decoration: none;">scattering of a <span style="color: windowtext; font-family: 'Times New Roman',Times,serif; font-size: 110%; text-decoration: none;">photon by an <span style="color: windowtext; font-family: 'Times New Roman',Times,serif; font-size: 110%; text-decoration: none;">atomic electron. It was derived before the advent of <span style="color: windowtext; font-family: 'Times New Roman',Times,serif; font-size: 110%; text-decoration: none;">quantum mechanics by <span style="color: windowtext; font-family: 'Times New Roman',Times,serif; font-size: 110%; text-decoration: none;">Hendrik Kramers and <span style="color: windowtext; font-family: 'Times New Roman',Times,serif; font-size: 110%; text-decoration: none;">Werner Heisenberg in 1925, based on the <span style="color: windowtext; font-family: 'Times New Roman',Times,serif; font-size: 110%; text-decoration: none;">correspondence principle applied to the classical dispersion formula for light. The <span style="color: windowtext; font-family: 'Times New Roman',Times,serif; font-size: 110%; text-decoration: none;">quantum mechanical derivation was given by <span style="color: windowtext; font-family: 'Times New Roman',Times,serif; font-size: 110%; text-decoration: none;">Paul Dirac in 1927. The Kramers-Heisenberg formula was an important achievement when it was published, explaining the notion of "negative absorption" ( <span style="color: windowtext; font-family: 'Times New Roman',Times,serif; font-size: 110%; text-decoration: none;">stimulated emission ), the Thomas-Reiche-Kuhn sum rule, and <span style="color: windowtext; font-family: 'Times New Roman',Times,serif; font-size: 110%; text-decoration: none;">inelastic scattering - where the <span style="color: windowtext; font-family: 'Times New Roman',Times,serif; font-size: 110%; text-decoration: none;">energy of the scattered photon may be larger or smaller than that of the incident photon - thereby anticipating the <span style="color: windowtext; font-family: 'Times New Roman',Times,serif; font-size: 110%; text-decoration: none;">Raman effect <span style="font-family: 'Times New Roman',Times,serif; font-size: 110%;">. http://en.wikipedia.org/wiki/Kramers-Heisenberg_formula http://en.wikipedia.org/wiki/Werner_Heisenberg

James Chadwick

<span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">James Chadwick discovered the neutron in 1932, resulting in the solution of the jig-saw puzzle for the weight of atoms. His discovery formed the base for the investigation of the tougher questions of nuclear physics: the nature of the nucleus and its forces. In 1935, he received the Nobel Prize for Physics. Chadwick was knighted in 1945, and died in 1974 at Cambridge.

<span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">Chadwick was born in 1891 in Manchester, England. He was graduated from Manchester University in 1911 and remained to work with Ernest Rutherford. In 1913, he received a scholarship to study in German, placing him in Germany at the beginning of World War I. After Chadwick was detained as a civilian prisoner of war, he returned to England in 1919 to carry out research at Cambridge University. In 1923, he became the assistant director of research at the Cavendish Laboratory.

<span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">Rutherford discovered that atoms have minute and dense nuclei, with the nucleus holding a positive charge in the charge of a hydrogen nucleus. Physicists wanted to determine where the extra mass was living. Chadwick helped answer this question when identifying the neutron (particle without an electric charge in the nucleus) in 1932. Chadwick had created an experiment to answer the question of this unknown nucleus mass source.

<span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">Chadwick smashed alpha particles into beryllium, a rare metallic element, and allowed the radiation that was released to hit another target: paraffin wax. When the beryllium radiation hit hydrogen atoms in the wax, the atoms were sent into a detecting chamber. In physics it is known that only a particle having almost the same mass as a hydrogen atom could effect hydrogen in that manner. The experiment results showed a collision with beryllium atoms would release massive neutral particles, which Chadwick named //neutrons//. This provided the answer for hidden mass in atoms.

<span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">Chadwick's discovery advanced experimental work for all scientists. Since neutrons have no electrical charge, any neutrons fired from a source has the ability to go through deep layers of materials and to go into the nuclei of the target atoms. After Chadwick's work, scientists world-wide began bombardment of all types of materials with neutrons. It was discovered that when uranium is a target, nuclear fission becomes possible, resulting in nuclear weapons and nuclear power plants.

<span style="font-family: 'Times New Roman','serif'; font-size: 12pt;">In 1935, Chadwick received the Nobel Prize for Physics for this discovery. During World War II, he worked with the British atomic bomb project, and was a science advisor to Oppenheimer on the Manhattan Project. The Manhattan Project was the first time an atomic bomb had been produced. Chadwick was knighted in 1945, and died in 1974 at Cambridge.

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