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=Atomic History Timeline =  By: Paulina Lardizabal and Allison Rivera  Ancient Times (450 AD and years prior)

Democritus
-Was born in 460 BCE in Abdera, in Northern Greece. He was an Ancient Greek philosopher; his atomic theory may be regarded as the culmination of early Greek thought. He was a strict determinist and a thorough materialist. He died in 370 BCE. Democritus’ philosophy states that an early form of the conservation of energy. In his theory atoms are eternal and so is motion. Demosctirus explained the origin of the universe through atoms moving randomly and colliding to form larger bodies and worlds. There was no place in his theory for divine intervention; he postulated a world which had always, and would alwas exist, and was filled with atoms moving randomly. He built an ethical theory on top of his atomist philosophy.

 Thales  -Born in Miletus in Asia Minor in 624 BC and died in 546 BC; the year of his discovery was during the sixth century. Thales is conventionally known for suposedly having acuired his leranings in Egypt, to him a proof is even attributed, the proof of the proposition that the circle is divided into two equal parts by its diameter, a theorem not to be found in Euclid some 300 years later. Historians have also reported that Thales gave a prediction of a solar eclipse in 585 **BC. With tales it is thought that astronomy, philosophy, physics and geometry ate thought to have begun.** His claim stated that everything is water, and probably the first recorded general physical principle in history. Thales' most famous belief was his cosmological thesis, which held that the world started from water.  Leucippus It is said Leucippus was born in Elea, Abdera or Miletus. He was born during the fifth century BC and died in 450 BC. Little is known about him, and his views are hard to distinguish from those of his associate Democritus. He is sometimes said to have been a student of Zeno of Elea, and to have devised the atomist philosophy in order to escape from the problems raised by Parmenides and his followers. Leucippus was the founder of Atomism. Year of discovery: First half of 5th Century B.C.

 1700-1800

Sir Isaac Newton **//-Isaac Newton was born in 1642 in a manor house in Lincolnshire, England. His father had died two months before his birth. When Isaac was three his mother remarried, and Isaac remained with his grandmother. He was not interested in the family farm, so he was sent to Cambridge University to study.Isaac thought the universe worked like a machine and that a few simple laws governed it. Like Galileo, he realized that mathematics was the way to explain and prove those laws. He was one of the world’s great scientists because he took his ideas, and the ideas of earlier scientists, and combined them into a unified picture of how the universe works. In old age Newton's health began to deteriorate: whe was eighty he began to suffer from incontinence, due to a weakness in the bladder, and his movement and diet became restricted. He ate mainly vegetables and broth, and was plagued by a stone in the bladder. In 1725 he fell ill with gout, and endured hemorrhoids the following year. Meanwhile, the pain from his bladder stones grew worse, and on March 19, 1727, he blacked out, never to regain consciousness. He died on March 20, at the age of eighty-five, and was buried in Westminster Abbey; his funeral attended by all of England's eminent figures, and his coffin carried by noblemen. It was, a contemporary noted, a funeral fit for a king.  //** He began experimenting with light, lenses, and prisms. He was trying to improve telescopes. He designed the reflecting telescope. The news and his reflecting telescope reached the newly formed Royal Society in London, and in 1671 he sent one as a gift. It caused somewhat of a stir, and following year Newton was elected a Fellow of the Society. Of all his greatest achievements, Newton is best known for his discovery of the laws of gravity and movement. The story goes that one day while he was sitting in his mother's orchard, an apple, which got him thinking, hit Newton. It involved the planets and how they move around the sun. One day, after finishing his work, Newton's dog came into the room. The dog jumped to the table and accidentally knocked over a candle, setting a fire to Newton's papers. Newton lost 20 years worth of work in the flame. He had to start again from scratch. <span style="color: #000080; font-family: Tahoma,Geneva,sans-serif; font-size: 120%;"> Antoine-Laurent Lavoisier <span style="font-family: Arial,Helvetica,sans-serif;"> -Was born August 26, 1743, the son of a wealthy Paris family. His father was a lawyer who had married a daughter of the wealthy Punctis family. Louis XV was the King of France. Most of Europe, and especially France, was in social upheaval. Peasants faced continual famines and peasant revolts and mob violence were common. Lavoisier's family were among the upper class so Lavoisier was able to complete a degree in law at the Collège Mazarin in fulfillment of his family's wishes. Despite all of the contributions to science and France made by Lavoisier in his 51-year life, it was his connection with the Ferme Générale that the revolution zealots noted. In November 1793, all 32 former members of the Ferme Générale were arrested and imprisoned. After a trial by jury, Antoine-Laurent Lavoisier, along with his father-in-law and, were found guilty of conspiracy against the people of France. He was guillotined on May 8, 1794. Year of Discovery: 1789. Discovery: The law of conservation of mass matter <span style="color: #000080; font-family: Tahoma,Geneva,sans-serif; font-size: 120%;">.

Humphry Davy <span style="color: #000000; font-family: Arial,Helvetica,sans-serif;">Humphry Davy, a woodcarver's son, was born in Penzance in 1778. After being educated in Truro, Davy was apprenticed to a Penzance surgeon. In 1797 he took up chemistry and was taken on by Thomas Beddoes, as an assistant at his Medical Pneumatic Institution in Bristol. Here he experimented with various new gases and discovered the anesthetic effect of laughing gas (nitrous oxide). One of Davy's most important contributions to history was that he encouraged manufacturers to take a scientific approach to production. His discoveries in chemistry helped to improve several industries including agriculture, mining and tanning. Sir Humphry Davy died in 1829. Year of Discovery:1800. He was a man that discovered several alkali and other alkali earth metals. One of his best discoveries was to find potassium in 1800. Before the 18th century, no distinction was made between potassium and sodium. Potassium was the first metal that was isolated by electrolysis. Davy first isolated sodium in the same year by passing an electric current through molten sodium hydroxide. Davy went on to discover calcium in 1808 by electrolyzing a mixture of lime and mercuric oxide. <span style="color: #000080; font-family: Tahoma,Geneva,sans-serif; font-size: 120%;">

<span style="color: #ff5300; font-family: 'Comic Sans MS',cursive; font-size: 150%;"> 1800-1875

<span style="color: #000080; font-family: Tahoma,Geneva,sans-serif; font-size: 120%;"> John Dalton -He was born about Sept. 6, 1766 (no exact record exists), in Eaglesfield. Until he was 11, he attended school, then at the age of 12 became a teacher. In 1837 he suffered a damaging stroke; the following year another left him with impaired speech. A final stroke came on the night of July 26, 1844. English meteorologist who switched to chemistry when he saw the applications for chemistry of his ideas about the atmosphere. He proposed the //Atomic Theory// in 1803 which stated that (1) all matter was composed of small indivisible particles termed atoms, (2) atoms of a given element possess unique characteristics and weight, and (3) three types of atoms exist: simple (elements), compound (simple molecules), and complex (complex molecules). Dalton's theory was presented in //New System of Chemical Philosophy// (1808-1827). This work identified chemical elements as a specific type of atom, therefore rejecting Newton's theory of chemical affinities. Instead, Dalton inferred proportions of elements in compounds by taking ratios of the weights of reactants, setting the atomic weight of hydrogen to be identically one. Following Richter, he proposed that chemical elements combine in integral ratios. Despite the importance of the work as the first view of atoms as physically real entities and introduction of a system of chemical symbols, <span style="font-family: Arial,Verdana,Helvetica,sans-serif; font-size: 12px; line-height: 18px;">//New System of Chemical Philosophy// devoted almost as much space to the caloric theory<span style="font-family: Arial,Helvetica,sans-serif; line-height: 18px;"> <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">as to atomism. <span style="color: #000080; font-family: Tahoma,Geneva,sans-serif; font-size: 132%;"> Frederick Abel <span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;"> <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">-Was born in London on the 17th of July 1827. After studying chemistry for six years under A. W. von Hofmann at the Royal College of Chemistry (established in London in 1845), he became professor of chemistry at the Royal Military Academy in 1851, and three years later was appointed chemist to the War Department and chemical referee to the government. During his tenure of this office, which lasted until 1888, he carried out a large amount of work in connexion with the chemistry of explosives.He passed away on Saturday, September 6, at the age of seventy-five, for some years he had been in failing health, but his sudden death, which came painlessly from cardiac failure following one of those attacks of shivering and rigor to which he had long been subject, was quite unexpected. Abel was a distinguished chemist and explosives specialist, he is remembered as oneof the inventors of cordite, a smokeless gunpowder still used today. During a lengthy career he served as a researcher, scholar, and lecturer, and became the leading British authority on explosives. One of his most significant early discoveries was that guncotton could bechemically stabilized through thorough washing with water to remove all traces of acid and impurities. His most important work, however, came after the British government's establishment in 1888 of an Explosives Commission, dedicated in particular to the military uses of new discoveries in the field. In 1889 Abel, together with JamesDewar, invented cordite, a versatile smokeless powder which purportedly improved upon ballistite through the introduction of acetone and petroleum jelly. <span style="color: #000080; font-family: Tahoma,Geneva,sans-serif; font-size: 120%;">Friherre Jöns Jacob Berzelius -Born in August 20, 1779 and died on August 7, 1848 in Sweden. As a Swedish chemist he worked out the modern technique of chemical formula notation, and is together with John Dalton, Antoine Lavoisier, and Robert Boyle considered a father of modern chemistry. He lost his both parents at early age, and was taken care by his relatives in Linköping where he attended the school today known as Katedralskolan. Year of Discovery:1851. Berzelius discovered the elements cerium (1803), selenium (1817), and thorium (1828). He isolated silicon (1823), zirconium (1824), and titanium (1825); classified minerals on a chemical basis; and made detailed studies of the compounds of tellurium, vanadium, molybdenum, tungsten, uranium, and other elements. Sometimes called the father of gravimetric analysis, he introduced the use of the water bath, desiccator, wash bottle, filter paper, rubber tubing, and improved blowpipe technique.

<span style="color: #ff5300; font-family: 'Comic Sans MS',cursive; font-size: 150%;"> 1875-1900

<span style="color: #000080; font-family: Tahoma,Geneva,sans-serif; font-size: 16px;">Charles Röntgen <span style="color: #000000; font-family: Arial,Helvetica,sans-serif;">-Wilhelm Conrad Röntgen was born on March 27, 1845, at Lennep in the Lower Rhine Province of Germany, as the only child of a merchant in, and manufacturer of, cloth. His mother was Charlotte Constanze Frowein of Amsterdam, a member of an old Lennep family which had settled in Amsterdam. He received his early education at the Institute of Martinus Herman van Doorn. In 1862, he attended Utrecht Technical School, from which he was expelled for producing a caricature of one of the teachers, a "crime" he claimed not to have committed. He died in February 10, 1923 in Munich, Germany, he died of cancer in the intestine. Roentgen observed in his dark laboratory the glowing of a fluorescent screen painted with barium platinocyanide placed in the path of the rays of a working Crookes tube which he had covered with black paper in order to exclude light. In a series of classical papers published between 1895 and 1897 he described the main properties of these unknown rays, which he therefore called X-rays. The picture that caught the scientific world by storm was the X-ray photograph of his wife’s hand, taken on December 22, 1895, which clearly showed the structure of the bones and the ring she was wearing. Roentgen demonstrated that the new rays were produced by the impact of cathode rays (electrons) on striking a target, which in Roentgen’s case was the glass envelope of the Crookes tube. It was left to Max von Laue (1879-1960) and his pupils to show that X-rays were a manifestation of highly energetic, invisible electromagnetic radiation. He produced and detected electromagnetic radiaton in a wave length range today known as x- rays or Rontgen rays. <span style="color: #000080; font-family: Tahoma,Geneva,sans-serif; font-size: 120%;">Marie Curie -Maria Sklodowska, was born in Warsaw on November 7, 1867, the daughter of a secondary-school teacher. She received a general education in local schools and some scientific training from her father. She became involved in a students' revolutionary organization and found it prudent to leave Warsaw, then in the part of Poland dominated by Russia, for Cracow, which at that time was under Austrian rule. In 1891, she went to Paris to continue her studies at the Sorbonne where she obtained Licenciateships in Physics and the Mathematical Sciences. She met Pierre Curie, Professor in the School of Physics in 1894 and in the following year they were married. She received many honorary science, medicine and law degrees and honorary memberships of learned societies throughout the world. Together with her husband, she was awarded half of the Nobel Prize for Physics in 1903, for their study into the spontaneous radiation discovered by Becquerel, who was awarded the other half of the Prize. In 1911 she received a second Nobel Prize, this time in Chemistry, in recognition of her work in radioactivity. Year of discovery: 1896. Her discovery was radioactive decay. A process where radiation and ionizing particles unstable the atomic nucleus by loosing energy. A process where radiation and ionizing particles unstable the atomic nucleus by loosing energy. Curie died in Savoy, France, after a short illness, on July 4, 1934.

<span style="color: #000080; font-family: Tahoma,Geneva,sans-serif; font-size: 120%;"> JJ Thomson <span style="font-family: Verdana,Arial,Helvetica,sans-serif; font-size: 11px; line-height: 15px;">**<span style="font-family: Arial,Helvetica,sans-serif; line-height: 16px;">Joseph John Thomson ** <span style="font-family: Arial,Helvetica,sans-serif; line-height: 16px;"> was born in Cheetham Hill, a suburb of Manchester on December 18, 1856. He enrolled at Owens College, Manchester, in 1870, and in 1876 entered Trinity College, Cambridge as a minor scholar. In 1890, he married Rose Elisabeth, daughter of Sir George E. Paget, K.C.B. They had one son, now Sir George Paget Thomson and i n 1937, and one daughter. He died in Cambridge, Cambridgeshire, England in 1940 and his cause of death is unkown. 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 Ernest Rutherford moved. Thomson's last important experimental program focused on determining the nature of positively charged particles. <span style="font-family: Arial,Helvetica,sans-serif; font-size: 12.1px; line-height: 16px;"> <span style="color: #000080; font-family: Tahoma,Geneva,sans-serif;"> <span style="color: #ff5300; font-family: 'Comic Sans MS',cursive; font-size: 150%;"> 1900-1915

<span style="color: #000080; font-family: Tahoma,Geneva,sans-serif; font-size: 120%;">Ernest Rutherford <span style="color: #000000; font-family: Arial,Helvetica,sans-serif;">-Was born on August 30, 1871 in Brightwater, New Zealand. Ernest Rutherford was the son of James Rutherford, a farmer, and his wife Martha Thompson, originally from Hornchurch, Essex, England. James had emigrated from Perth, Scotland, "to raise a little flax and a lot of children". Ernest was born at Spring Grove, near Nelson, New Zealand. His first name was mistakenly spelled //<span style="color: #000000; font-family: Arial,Helvetica,sans-serif;">Earnest // <span style="color: #000000; font-family: Arial,Helvetica,sans-serif;"> when his birth was registered. He was admitted to the Order of Merit in 1925 and in 1931 was created **<span style="color: #000000; font-family: Arial,Helvetica,sans-serif;">Baron Rutherford of Nelson ** <span style="color: #000000; font-family: Arial,Helvetica,sans-serif;">, of Cambridge in the County of Cambridge, a title that became extinct upon his unexpected death in hospital following an operation for an umbilical hernia in 1937. He discovered that atoms have their positive charge concentrated in a very small nucleus, and thereby pioneered the Rutherford model, or planetary, model of the atom, through his discovery and interpretation of Rutherford sacttering in his gold foil experiment. He was awarded the Nobel Prize in Chemistry in 1908. He is widely credited as splitting the atom in 1917 and leading the first experiment to "split the nucleus" in a controlled manner by two students under his direction, John Cockcroft and Ernest Walton in 1932.

<span style="color: #000080; font-family: Tahoma,Geneva,sans-serif; font-size: 120%;"> Antoine Henri Becquerel -Was born in Paris on December 15, 1852, a member of a distinguished family of scholars and scientists. His father, Alexander Edmond Becquerel, was a Professor of Applied Physics and had done research on solar radiation and on phosphorescence, while his grandfather, Antoine César, had been a Fellow of the Royal Society and the inventor of an electrolytic method for extracting metals from their ores. He entered the Polytechnic in 1872, then the government department of Ponts-et-Chaussées in 1874, becoming ingénieur in 1877 and being promoted to ingénieur-en-chef in 1894. In 1888 he acquired the degree of docteur-ès-sciences. From 1878 he had held an appointment as an Assistant at the Museum of Natural History, taking over from his father in the Chair of Applied Physics at the Conservatoire des Arts et Metiers. In 1892 he was appointed Professor of Applied Physics in the Department of Natural History at the Paris Museum. He became a Professor at the Polytechnic in 1895. Year of radioactivity discovery: 1896. Antoine Henri Becquerel died at Le Croisic on August 25, 1908.

<span style="color: #000080; font-family: Tahoma,Geneva,sans-serif; font-size: 120%;">Robert Andrews Millikan -Was born on the 22nd of March, 1868, in Morrison, Ill. (U.S.A.), as the second son of the Reverend Silas Franklin Millikan and Mary Jane Andrews. His grandparents were of the Old New England stock, which had come to America before 1750, and were pioneer settlers in the Middle West. He led a rural existence in childhood, attending the Maquoketa High School (Iowa). After working for a short time as a court reporter, he entered Oberlin College (Ohio) in 1886. During his undergraduate course his favourite subjects were Greek and mathematics; but after his graduation in 1891 he took, for two years, a teaching post in elementary physics. It was during this period that he developed his interest in the subject in which he was later to excel. In 1893, after obtaining his mastership in physics, he was appointed Fellow in Physics at Columbia University. He afterwards received his Ph.D. (1895) for research on the polarization of light emitted by incandescent surfaces - using for this purpose molten gold and silver at the U.S. Mint. Year of discovery: 1913. He died on the 19th of December, 1953, in San Marino, California.

<span style="color: #ff5300; font-family: 'Comic Sans MS',cursive; font-size: 150%;"> 1915-1950

<span style="color: #000080; font-family: Tahoma,Geneva,sans-serif; font-size: 120%;"> Niels Henrik David Bohr -Was born in Copenhagen on October 7, 1885, as the son of Christian Bohr, Professor of Physiology at Copenhagen University, and his wife Ellen, née Adler. Niels, together with his younger brother Harald (the future Professor in Mathematics), grew up in an atmosphere most favourable to the development of his genius - his father was an eminent physiologist and was largely responsible for awakening his interest in physics while still at school, his mother came from a family distinguished in the field of education. Year of discovery: 1922. Niels Bohr was the Danish physicist whose investigations of atomic structure earned him the 1922 Nobel Prize for physics. Bohr's work helped solve the problems classical physics could not explain about the nuclear model of the atom. He postulated that electrons moved in fixed orbits around the atom's nucleus, and he explained how they emitted or absorbed energy. Niels Bohr died in Copenhagen on November 18, 1962.

<span style="color: #000080; font-family: Tahoma,Geneva,sans-serif; font-size: 120%;">Werner Heisenberg -He was born in December 5, 1901 Würzburg, Germany and died on February 1, 1976 in Munich, Germany. He was a German theoretical physicist that made foundational contributions to quantum mechanics. Heisenberg is best known for asserting the uncertainty principle of quantum theory. In addition to this, he also made very important contributions t nuclear physics, particle physics and quantum field theory. He stated that the act of observation interfered with the location and velocity of small particles such as electrons. When light bounces off an electron momentum exchange can occur between light and the electron which means the electrons location and velocity have been altered by the act of measurement. This is the case because observation requires light and light has momentum.

<span style="color: #000080; font-family: Tahoma,Geneva,sans-serif; font-size: 120%;">James Chadwick -Was born in Cheshire, England, on 20th October, 1891, the son of John Joseph Chadwick and Anne Mary Knowles. He attended Manchester High School prior to entering Manchester University in 1908; he graduated from the Honors School of Physics in 1911 and spent the next two years under Professor (later Lord) Rutherford in the Physical Laboratory in Manchester, where he worked on various radioactivity problems, gaining his M.Sc. degree in 1913. That same year he was awarded the 1851 Exhibition Scholarship and proceeded to Berlin to work in the Physikalisch Technische Reichsanstalt at Charlottenburg under Professor H. Geiger. In 1925, he married Aileen Stewart-Brown of Liverpool. They have twin daughters, and live at Denbigh, North Wales. His hobbies include gardening and fishing. Year of discovery: 1932. Chadwick's early experiments established the number of protons in an atom determines that atomic number.

<span style="color: #000080; font-family: Tahoma,Geneva,sans-serif; font-size: 120%;">Erwin Schrödinger -Was born on August 12, 1887, in Vienna, the only child of Rudolf Schrödinger, who was married to a daughter of Alexander Bauer, his Professor of Chemistry at the Technical College of Vienna. Schrödinger's wide interests dated from his school years at the Gymnasium, where he not only had a liking for the scientific disciplines, but also appreciated the severe logic of ancient grammar and the beauty of German poetry. (What he abhorred was memorizing of data and learning from books.) After his retirement he returned to an honored position in Vienna. He died on the 4th of January, 1961, after a long illness, survived by his faithful companion, Annemarie Bertel, whom he married in 1920. Year of discovery: 1933. He achieved fame for his contributions to quantum mechanics, especially the Schrödinger equation, for which he received the Nobel Prize in 1933.

<span style="color: #ff0000; font-family: Impact,Charcoal,sans-serif; font-size: 200%;">Atomic Models' Timeline

<span style="color: #008000; font-family: 'Comic Sans MS',cursive; font-size: 130%;">Dalton's Model- 1803 <span style="color: #000000; font-family: Arial,Helvetica,sans-serif;"> Dalton's theory was based on the principle that atoms of different elements could be distinguished by differences in their weights. His theory, states at a lecture to the Royal Institution in 1803, proposed a number of basic ideas, such as: <span style="color: #000000; font-family: Arial,Helvetica,sans-serif;"> <span style="color: #000000; font-family: Arial,Helvetica,sans-serif;"> <span style="color: #000000; font-family: Arial,Helvetica,sans-serif;"> <span style="color: #000000; font-family: Arial,Helvetica,sans-serif;"> <span style="font-family: Arial,Helvetica,sans-serif;"> <span style="font-family: Arial,Helvetica,sans-serif; font-size: 130%;"> <span style="font-family: Arial,Helvetica,sans-serif;">Using his theory, Dalton rationalized the various laws of chemical combinations that existed at that time, and provided a logical explanation of concepts. He stated that elements consisted of tiny particles called atoms and called elements pure substances because all atoms of an element were identical and that in particular they had the same mass. Dalton's model was that the atoms were tiny, indivisible, indestructible particles and that each one had a certain mass, size, and chemical behavior that was determined by what kind of element they were. <span style="color: #000000; font-family: Arial,Helvetica,sans-serif; font-size: 130%;">
 * <span style="color: #000000; font-family: Arial,Helvetica,sans-serif;">All matter is composed of atoms
 * <span style="color: #000000; font-family: Arial,Helvetica,sans-serif;">Atoms cannot be made or destroyed
 * <span style="color: #000000; font-family: Arial,Helvetica,sans-serif;">All atoms of the same element are identical
 * <span style="color: #000000; font-family: Arial,Helvetica,sans-serif;">Different elements have different types of atoms
 * <span style="color: #000000; font-family: Arial,Helvetica,sans-serif;">Chemical reactions occur when atoms are rearranged
 * <span style="font-family: Arial,Helvetica,sans-serif;">Compounds are formed from atoms of the constituent elements

<span style="color: #128746; font-family: 'Comic Sans MS',cursive; font-size: 169%;">Plum Pudding Model <span style="color: #128746; font-family: 'Comic Sans MS',cursive; font-size: 17px; line-height: 25px;">- 1904 <span style="font-family: Arial,Helvetica,sans-serif;"> 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 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 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: #128746; font-family: 'Comic Sans MS',cursive; font-size: 150%;">Rutherford-B <span style="color: #128746; font-family: 'Comic Sans MS',cursive; font-size: 150%;">ohr Model- 1 <span style="color: #128746; font-family: 'Comic Sans MS',cursive; font-size: 150%;">911-1913 Developed by Ernest Rutherford and Neils Bohr, this model was an important step in understanding the structure of the atom. Rutherford's gold foil experiment led him to the discovery of the dense central region within a primarily entry space in each atom. He also concluded that since positively charged partials bounced back, the central region must have a positive charge. These two scientists created this model in such a way that the electrons travel around the nucleus in an orbit al fashion. There are different levels upon which these negatively charged partials travel. The further away from the nucleus, the more energy they have. Though not perfect by today’s standards, the model was a breakthrough at the time.

<span style="color: #128746; font-family: 'Comic Sans MS',cursive; font-size: 150%;"> Planetary Model <span style="font-family: Calibri,sans-serif; font-size: 15px; line-height: 22px;">The planetary model of the atom assumed that the electrostatic attraction between the central nucleus and the electron is exactly balanced by the centrifugal force created by the revolution of the electron in its orbit. If this balance were not present, the electron would either fall into the nucleus, or it would be flung out of the atom.

<span style="color: #128746; font-family: 'Comic Sans MS',cursive; font-size: 150%;">Electron Coud Model- 1920s <span style="font-family: Arial,Helvetica,sans-serif;">An atom consists of a dense nucleus composed of protons and neutrons surrounded by electrons that exist in different clouds at the various energy levels. Erwin Schrodinger and Werner Heisenburg developed probability functions to determine the regions or clouds in which electrons would most likely be found.

<span style="color: #800080; font-family: Impact,Charcoal,sans-serif; font-size: 130%;"> __Bibliography__ -http://scienceworld.wolfram.com/biography/Dalton.html -http://www.bookrags.com/J._J._Thomson -http://www.answers.com/topic/frederick-augustus-abel -http://uk.encarta.msn.com/encyclopedia_761555545/roentgen_wilhelm_conrad.html -http://nobelprize.org/nobel_prizes/physics/laureates/1903/marie-curie-bio.html -http://inventors.about.com/library/inventors/blnewton.htm -http://www.rutherford.org.nz/hrstampnz1.htm -http://nobelprize.org/nobel_prizes/physics/laureates/1903/becquerel-bio.html -http://www.sparknotes.com/biography/newton/section9.rhtml -http://nobelprize.org/nobel_prizes/physics/laureates/1922/bohr-bio.html -http://en.wikipedia.org/wiki/Niels_Henrik_David_Bohr -http://nobelprize.org/nobel_prizes/physics/laureates/1923/millikan-bio.html -http://plato.stanford.edu/entries/leucippus/ -http://nobelprize.org/nobel_prizes/physics/laureates/1935/chadwick-bio.html -http://nobelprize.org/nobel_prizes/physics/laureates/1933/schrodinger-bio.html -http://mattson.creighton.edu/History_Gas_Chemistry/Lavoisier.html