reich.atomichistorytimeline.fall.2011

__Empedocles (490BC-430BC) Sicily__ His philosophy of the four elements in the universe and the definition of matter as the various ratios of these elements foreshadowed later developments in atomic theory by other philosophers. He said these 4 elements were earth, fire, wind, and water that were able to create all things including living by different mixtures and solutions. He called these elements “roots”. He also said that the elements are external and unchanging, and each element retains its own characteristics in nature. __Democritus (460BC-370BC) Greece__ Took his speculation on atoms from mentor Leucippus, and was said to be more of a scientist than other Greek Philosophers. Liked by Aristotle and hated by Plato, he is said to be the father of modern science. The theory of Democritus and Leucippus held that everything is composed of "atoms", which are physically, but not geometrically, indivisible; that between atoms lies empty space; that atoms are indestructible; have always been, and always will be, in motion; that there are an infinite number of atoms, and kinds of atoms, which differ in shape, and size. Of the mass of atoms, Democritus said "The more any indivisible exceeds, the heavier it is." But his exact position on weight of atoms is disputed. __Aristotle (384BC-322BC) Greece__ The most famous student of the Athenian philosopher Plato was Aristotle. After the death of his master, he studied biology and accepted a position as teacher of the Macedonian crown prince Alexander. When the Macedonians subdued Greece, Aristotle founded a school at Athens. Most of his writings are lost; what remains are his lecture notes, which were rediscovered in the first century BCE. During the last decades, scholars have started to re-examine the fragments of the lost works, which has led to important changes in our understanding of Aristotle's philosophy. His main works are the Prior Analytics (in which he described the rules of logic), the Physics, the Animal History, the Rhetorics, the Poetics, the Metaphysics, the Nicomachean Ethics, and the Politics. He did not believe in the atom, he believed that all things were made up of different proportions of fire, earth, wind, and water. __Joseph Black (1728-1799) Scotland__ A Scottish physician and chemist, Black discovered latent heat, specific heat, and carbon dioxide. He was professor of Medicine at University of Glasgow, where he also served as lecturer in Chemistry. James Watt, who was appointed as philosophical instrument maker at the same university in 1756 and consulted with Black on experiments with his steam engine. Watt and Black also collaborated in project to manufacture sodium hydroxide. The chemistry buildings at both the University of Edinburgh and the University of Glasgow are named after Black. __Antoine Lavoisier (1743-1794) France__ Also known as the “father of modern chemistry”, Lavoisier was a French nobleman in the studies of chemistry and biology. He termed both oxygen in 1778 and hydrogen in 1783, helped build the metric system, put together the first list of elements, and helped to reform chemical nomenclature, disproved the phlogiston theory, and was the first to divise the law of conservation of mass. He was also the first to establish that sulfur was an element in 1777 rather than a compound. He discovered that, although matter may change its form or shape, its mass always remains the same. He was guillotined at the height of the French Revolutions under accusations of selling watered down tobacco. __Henry Cavendish (1731-1810) Britain__ He was noted for his discovery of “inflammable air” or hydrogen gas, which formed water on combustion in 1766. He was also the first to research the force of gravity, his measurement in earth’s density, and had early experiments in electricity. He was able to create, isolate, and study hydrogen molecules by combining strong metals with acid. He also helped determine the composition of earth’s atmosphere. Much of his work is similar to that of Antoine Lavoisier. __John Dalton (1766-1844) England__ Experimented in the constitution of gasses, on the pressure of steam and other vapors at different temperatures, both in a vacuum and in air, on evaporation, and on the thermal expansion, of gases. Described Dalton’s Law in both chemistry and physics, states that the total pressure exerted by a gaseous mixture is equal to the sum of the partial pressures of each individual component in a gas mixture. This empirical law was observed by John Dalton in 1801 and is related to the ideal gas laws. He researched ethylene and methane or by analysis of nitrous oxide and nitrogen dioxide. However, a study of Dalton's own laboratory notebooks, discovered in the rooms of the Lit & Phil, concluded that so far from Dalton being led by his search for an explanation of the law of multiple proportions to the idea that chemical combination consists in the interaction of atoms of definite and characteristic weight, the idea of atoms arose in his mind as a purely physical concept, forced upon him by study of the physical properties of the atmosphere and other gases. Dalton also had 5 main points in atomic theory, 1. Elements are made of extremely small particles calledatoms. 2. Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties. 3. Atoms cannot be subdivided, created, or destroyed. 4. Atoms of different elements combine in simple whole-number ratios to form chemical compounds. 5. In chemical reactions, atoms are combined, separated, or rearranged. The first step in the modernly accept model of an atom was the model proposed by John Dalton and the scientists that preceded him. To Dalton, atoms were tiny, spherical, indivisible, solid particles that somehow attached to one another to form molecules. This model is the first step to the current model of atoms, but lacks much of the complexity found in an atom. Nothing is mentioned about any of the three types of subatomic particles, nor the placement of the electrons. Dalton's theory also proposed that atoms could not be separated in any way, and since the discovery of modern nuclear chemistry, this has been disproved. __Germain Hess (1802-1850) Russia__ He formulated and described “Hess’s Law” which was an early concept of thermochemisty. In 1830, Hess took up chemistry full time, researching and teaching, and later became a professor at the Saint Petersburg Technological Institute. His most famous paper, outlining his law on thermochemistry, was published there in 1840. His principle, a progenitor for the first law of thermodynamics, came to be called Hess's Law. It states that in a series of chemical reactions, the total energy gained or lost depends only on the initial and final states, regardless of the number or path of the steps. This is also known as the law of constant heat summation. __Lord Kelvin (1824-1907) Ireland__ In 1851 he published ideas leading to the second law of thermodynamics and supported his friend James Joule's mechanical equivalent of heat. He changed the view of heat as being a fluid to an understanding of the energy of motion of molecules. The term "kinetic energy" was introduced by Thomson in 1856. The names of these two scientists are linked with the famous Joule-Kelvin Effect which makes refrigerators work. Most well known for discovering absolute zero, and development of the Kelvin temperature scale based off of the Celsius temperature scale.
 * __Ancient Years__**
 * __1700-1800__**
 * __1800-1875__**

__Henri Becquerel (1852-1908) France__ In 1896, while investigating phosphorescence in uranium salts, Becquerel accidentally discovered radioactivity. Becquerel wrapped a fluorescent substance, potassium uranyl sulfate, in photographic plates and black material in preparation for an experiment requiring bright sunlight. However, prior to actually performing the experiment, Becquerel found that the photographic plates were already exposed, showing the image of the substance. This discovery led Becquerel to investigate the spontaneous emission of nuclear radiation. __Wilhelm Rontgen (1845-1925) Germany__ Wilhelm was born in Germany in 1845 and he studied at the University of Zurich. In 1895 Rontgen produced and detected electromagnetic radiation in a wavelength known today as x-rays. Rontgen was awarded the Nobel Prize for his discovery in 1901. In keeping with his will all his scientific and personal correspondents was destroyed when he died in 1925. __Sir Joseph John Thompson (December 18th 1856-August 30th 1940)__ Country of origin: United Kingdom JJ Thompson was born in England and studied at Owens College and Cambridge. In 1906 Thompson discovered the electron through his experiments with cathode rays. Thompson received a Nobel Prize for his discovery in 1906. Thompson also developed the plum pudding model for atoms which was later disproved by Ernest Rutherford. Thompson died in 1940 and was buried close to Isaac Newton. 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 order to add the electron to the atomic model. __Marie Curie (November 7th 1867- July 4th 1934)__ Country of origin: Poland Marie Curie was born in the kingdom of Poland in 1867 and a pioneering woman scientist that succeeded in multiple scientific fields. In 1911 she received a Nobel Prize in chemistry for her theory of radioactivity and the discovery of two new elements polonium and radium. She also helped the polish war effort during the First World War by donating her Nobel Prize metals to help the war effort and by helping pioneer new ways to treat wounded soldiers. She died in 1934 because of her constant exposure to radiation during her studies. __Robert Millikan (March 22nd 1868-December 19th 1953)__ Country of Origin: United States of America Robert Millikan was born in Illinois in 1868 and studied at Colombia University. Millikan is famous for discovering the charge of an electron during his famous oil drop experiment in 1910. He later received Nobel Prize for his work in 1923. Millikan died of a heart attack in 1953. __Ernest Rutherford (August 30th 1871-October 19th 1937)__ Country of origin: New Zealand Ernest Rutherford was born in New Zealand in 1871; He studied at the University of New Zealand but later traveled to England to continue his studies. Rutherford is famous for his gold foil experiment which for the first time reviled the existence of the nucleus and disproved the plumb pudding model, and helps further the understanding of the atom and sub atomic particles. Rutherford died in 1937 and was buried in Westminster Abby close to Isaac Newton’s tomb. __Niels Bohr (October 7th 1885-November 18th 1962)__ Country of origin: Denmark Niels Bohr was born in Copenhagen Denmark in 1885 and studied at Copenhagen University and did experiments under JJ Thompson at Cambridge University in England. In 1913 he developed the model for the hydrogen atom and the orbitals of the electrons and how they follow specific orbits around the nucleus. This became known as the planetary model or the Bohr- Rutherford model. Bohr also worked on the Manhattan Project in the United States during World War Two helping to develop the first atomic bomb. After the war Bohr helped to find peaceful uses for atomic energy and died of heart failure in 1962. This model depicts the atom as a positively charged nucleus with electrons that orbit the nucleus in orbital patterns. It was introduced by Niels Bohr in 1913 and is a modification of the Rutherford model. The model was proposed when Bohr proposed that electrons only move in specific orbitals around a positively charged nucleus. Bohr also proposed that electrostatic forces keep the electrons in there orbit and are the reason why they follow specific orbital paths. This model is also known as the Planetary Model.
 * __1875-1900__**
 * __1900-1915__**

__Erwin Schrodinger (August 12th 1887-January 4th 1967)__ Country of origin: Austria Erwin Schrodinger was born in Austria in 1887 and is famous for developing the Schrodinger Equation that deals with electrons and waves; the equation was developed in 1926. Schrodinger did most of his work in Germany before leaving in 1933 because of his opposing views against the Nazis he later wrote a letter contradicting this which stirred up trouble with him living in England at this time, so he moved to Ireland and set up the Dublin Institute of Advanced Studies and later returned to Austria where he died of tuberculosis in 1967. Electron Cloud Model This model describes electron orbitals as a mathematical function that portrays the wave like behavior of an electron in an atom. This model can be used to calculate the probability of finding an electron in the regions around the nucleus.
 * __1915-1950__**

__James Chadwick (October 20th 1891-July 24th 1974)__ Country of Origin: United Kingdom James Chadwick was born in England in 1891 and studied at the University of Manchester and the University of Cambridge. Chadwick is credited with discovering the neutron in 1932 when he calculated the mass of this neutral particle. Chadwick was also the only British scientist to work on the Manhattan Project to develop the first atomic bomb; he was knighted for his efforts in this project. Chadwick was also a professor at the University of Liverpool and died at the age of 82 in 1974. __Werner Heisenberg (December 5th 1901-Febuary 1st 1976)__ Country of Origin: Germany Werner Heisenberg was born in 1901 in Germany and is credited with creating the Heisenberg Uncertainty Principal which states that it is impossible to determine both, the position and velocity of an electron or any other particle, this is proven in the electron cloud model. Heisenberg received a Nobel Prize in 1932 and worked for the Nazis during the Second World War. He died at the age of 74 in West Germany. __ Albert Einstein (March 14th 1879-April 18th 1955) __ Country of Origin: Germany Albert Einstein was one of the most famous scientists of all time he was born in Germany 1879 where he excelled in many scientific fields. In 1933 while visiting the United States Adolf Hitler came to power in Germany and Einstein did not return to Germany. During this time he was deeply involved in the Manhattan Project and helped the United States to develop the first atomic bomb though he was against using the weapon. Einstein became a United States citizen in 1940 and after the war he worked at Princeton University until his death in 1955. He is credited with publishing over 300 scientific works and over 150 un-scientific works. Works Citied

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