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​Timeline: Jose Miguel Orellana

Name: Democritus Date: ca. 460 BCE – ca. 370 BCE Counrty: Greece Year of Discovery: (no data) Biography: His exact contributions are difficult to disentangle from his mentor Leucippus, as they are often mentioned together in texts. Their hypothesis on atoms is remarkably similar to modern science, and avoided many of the errors found in their contemporaries. Largely ignored in Athens, Democritus was nevertheless well-known to his fellow northern-born philosopher Aristotle. Plato is said to have disliked him so much that he wished all his books burnt. Many consider Democritus to be the "father of modern science". Discovery: Atomic hypothesis. The hypothesis of Leucippus and Democritus held everything to be 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, size, and temperature. Of the weight of atoms, Democritus said "The more any indivisible exceeds, the heavier it is." But their exact position on weight of atoms is disputed. Leucippus is widely credited with being the first to develop the theory of atomism. Nevertheless, this notion has been called into question by some scholars. Newton, for instance, credits the obscure Moschus the Phoenician (whom he believed to be the biblical Moses) as the inventor of the idea. The //Stanford Encyclopedia of Philosophy// notes that "This theologically motivated view does not seem to claim much historical evidence, however." Aristotle criticized the atomists for not providing an account for the cause of the original motion of atoms, but in this they have been vindicated as more scientific than their critics. Even if a prime mover or creator is supposed, that force remains unaccounted for. The theory of the atomists is, in fact, more nearly that of modern science than any other theory of antiquity. However, their theories were not wholly empirical, and their belief was devoid of any solid foundation. The atomists can be viewed as having hit on a hypothesis for which, two thousand years later, some evidence happened to be found.
 * __Ancient Times__
 * 1) Democritus[[image:http://upload.wikimedia.org/wikipedia/commons/thumb/7/70/Demokrit.jpeg/200px-Demokrit.jpeg width="200" height="243" align="right" link="http://en.wikipedia.org/wiki/File:Demokrit.jpeg"]]
 * Democritus** was an Ancient Greek philosopher born in Abdera in the north of Greece. He was the most prolific, and ultimately the most influential, of the pre-Socratic philosophers; his atomic theory may be regarded as the culmination of early Greek thought.

2. Leucippus Name: Leucippus Date: 1st half of 5th Century BC Country: Greece Year of Discovery: 5th Century Biography: Leucippus or Leukippos was the first Greek to develop the theory of atomism — the idea that everything is composed entirely of various imperishable, indivisible elements called atoms — which was elaborated in far greater detail by his pupil and successor, Democritus. He was born at Miletus or Abdera. Leucippus was a shadowy figure, as his dates are not recorded and he is often mentioned in conjunction with his more well-known pupil Democritus. It is therefore difficult to determine which contributions come from Democritus or from those of Leucippus. Leucippus was a contemporary of Zeno, Empedocles and Anaxagoras of the Ionian school of philosophy. Leucippus was most influenced by Zeno, who possessed a great interest in the problems and paradoxes of space. He studied at the school in Elea, but it is not certain whether this was before or after the death of Parmenides. Around 440 B.C. or 430 B.C. Leucippus founded a school at Abdera, which his pupil, Democritus, was closely associated with. His fame was so completely overshadowed by that of Democritus, who systematized his views on atoms, that Epicurus doubted his very existence, according to Diogenes Laertius.

Discovery: Theory of Atomism. Atomism is a natural philosophy developed by Leucippus and his student Democritus in the fifth century BC. These atomists theorized that the natural world consists of two fundamental and opposite, indivisible bodies - atoms and void (//void// is mere nothing, or the body's negation). Atoms are intrinsically unchangeable and move about the void combining into different clusters (and these clusters form deferring substances). Atoms are reality's very small, indestructible building blocks (Aristotle, //Metaphysics//, I, 4, 985 b, 10-15). The word atomism derives from the ancient Greek adjective //atomos//, which literally meant 'uncuttable' (//a// - //tomos// (//not cuttable//) - //tomos// a conjugate of the Greek verb //temnein// (//to cut//)). Of importance to the philosophical concept of atomism is the historical accident that the particles that chemists and physicists of the early 19th century thought were indivisible, and therefore identified with the uncuttable //a-toms// of long tradition, were found in the 20th century to be composed of even smaller entities: electrons, neutrons, and protons. Further experiments showed that protons and neutrons are made of fundamental quarks. These particles at present show no experimental evidence of size or substructure. Thus, as regards quarks, electrons, and other fundamental leptons are concerned, the possibility that they too are composed of smaller particles cannot be ruled out. In the meantime, however, it is these particles (not chemical atoms) which remain the best candidates for the traditional indivisible objects, with which historical atomism has concerned itself.

3. Thales Name: Thales of Miletus Date: ca. 624 BC–ca. 546 BC Country: Greece Year of Discovery: around 500 BC Biography: Thales of Miletus was a pre-Socratic Greek philosopher from Miletus in Asia Minor, and one of the Seven Sages of Greece. Many, most notably Aristotle, regard him as the first philosopher in the Greek tradition. According to Bertrand Russell, "Western philosophy begins with Thales." Thales lived around the mid 620s – mid 540s BC and was born in the city of Miletus. Miletus was an ancient Greek Ionian city on the western coast of Asia Minor (in what is today the Aydin Province of Turkey) near the mouth of the Maeander River. Discovery: Thales theorem. In geometry, **Thales' theorem** (named after Thales of Miletus) states that if A, B and C are points on a circle where the line AC is a diameter of the circle, then the angle ABC is a right angle. Thales' theorem is a special case of the inscribed angle theorem.

Name: Sir Isaac Newton Date: 4 January 1643 – 31 March 1727 Country: England Year of Discovery: 1713 Biography: Isaac Newton was born on 4 January 1643 at Woolsthorpe Manor in Woolsthorpe-by-Colsterworth, a hamlet in the county of Lincolnshire. At the time of Newton's birth, England had not adopted the Gregorian calendar and therefore his date of birth was recorded as Christmas Day, 25 December 1642. Newton was born three months after the death of his father, a prosperous farmer also named Isaac Newton. Born prematurely, he was a small child; his mother Hannah Ayscough reportedly said that he could have fit inside a quart mug (≈ 1.1 litre). When Newton was three, his mother remarried and went to live with her new husband, the Reverend Barnabus Smith, leaving her son in the care of his maternal grandmother, Margery Ayscough. The young Isaac disliked his stepfather and held some enmity towards his mother for marrying him, as revealed by this entry in a list of sins committed up to the age of 19: "Threatening my father and mother Smith to burn them and the house over them." From the age of about twelve until he was seventeen, Newton was educated at The King's School, Grantham (where his signature can still be seen upon a library window sill). He was removed from school, and by October 1659, he was to be found at Woolsthorpe-by-Colsterworth, where his mother, widowed by now for a second time, attempted to make a farmer of him. He hated farming. Henry Stokes, master at the King's School, persuaded his mother to send him back to school so that he might complete his education. Motivated partly by a desire for revenge against a schoolyard bully, he became the top-ranked student. Discovery: //Philosophiæ Naturalis Principia Mathematica// (usually called the //Principia//) is considered to be among the most influential books in the history of science, laying the groundwork for most of classical mechanics. In this work, Newton described universal gravitation and the three laws of motion which dominated the scientific view of the physical universe for the next three centuries. Newton showed that the motions of objects on Earth and of celestial bodies are governed by the same set of natural laws by demonstrating the consistency between Kepler's laws of planetary motion and his theory of gravitation, thus removing the last doubts about heliocentrism and advancing the scientific revolution. In mechanics, Newton enunciated the conservation principles of momentum and angular momentum. In optics, he built the first practical reflecting telescope[8] and developed a theory of colour based on the observation that a prism decomposes white light into the many colours that form the visible spectrum. He also formulated an empirical law of cooling and studied the speed of sound. In mathematics, Newton shares the credit with Gottfried Leibniz for the development of the differential and integral calculus. He also demonstrated the generalised binomial theorem, developed the so-called "Newton's method" for approximating the zeroes of a function, and contributed to the study of power series.
 * __1700-1800__
 * 1) Isaac Newton

2. Antoine Lavoisier Name: Antoine-Laurent de Lavoisier Date: 26 August 1743 – 8 May 1794 Country: France Year of Discovery: 1789 Biography: Born to a wealthy family in Paris, Antoine Laurent Lavoisier inherited a large fortune at the age of five with the passing of his mother.[5] He attended the College Mazarin in 1754 to 1761, studying chemistry, botany, astronomy, and mathematics. His education was filled with the ideals of the French Enlightenment of the time, and he felt fascination for Maquois's dictionary. He attended lectures in the natural sciences. Lavoisier's devotion and passion for chemistry was largely influenced by Étienne Condillac, a prominent French scholar of the 18th century. His first chemical publication appeared in 1764. In collaboration with Jean-Étienne Guettard, Lavoisier worked on a geological survey of Alsace-Lorraine in June 1767. At the age of 25, he was elected a member of the French Academy of Sciences, France's most elite scientific society, for an essay on street lighting and in recognition for his earlier research. In 1769, he worked on the first geological map of France. In 1771, Lavoisier at age 28, married the 13-year-old Marie-Anne Pierrette Paulze, the daughter of a co-owner of the Ferme. Over time, she proved to be a scientific colleague to her husband. She translated documents from English for him, including Richard Kirwan's //Essay on Phlogiston// and Joseph Priestley's research. She created many sketches and carved engravings of the laboratory instruments used by Lavoisier and his colleagues. She also edited and published Lavoisier’s memoirs (whether any English translations of those memoirs have survived is unknown as of today) and hosted parties at which eminent scientists discussed ideas and problems related to chemistry. Discovery: List of Elements. Lavoisier's //Traité Élémentaire de Chimie (Elementary Treatise of Chemistry//, 1789, translated into English by Robert Kerr) is considered to be the first modern chemical textbook. It contained a list of elements, or substances that could not be broken down further, which included oxygen, nitrogen, hydrogen, phosphorus, mercury, zinc, and sulfur. It also forms the basis for the modern list of elements. His list, however, also included light and caloric, which he believed to be material substances. While many leading chemists of the time refused to believe Lavoisier's new revelations, the //Elementary Treatise// was written well enough to convince the younger generation. However, as Lavoisier's descriptions only classified elements into metals and non-metals, it fell short of a complete analysis.

3. Humphry Davy Name: Sir Humphry Davy Date: 17 December 1778 – 29 May 1829 Country: England Year of Discovery: around 1800 Biography: Davy was born at Penzance in Cornwall on 17 December 1778. The parish register of Madron (the parish church) records ‘Humphry Davy, son of Robert Davy, baptized at Penzance, January 22nd, 1779.’ Robert Davy was a wood-carver at Penzance, who pursued his art rather for amusement than profit. As the representative of an old family (monuments to his ancestors in Ludgvan Church date as far back as 1635), he became possessor of a modest patrimony. His wife,Grace Millet, came of an old but no longer wealthy family. Her parents died within a few hours of each other from malignant fever, when Grace and her two sisters were adopted by John Tonkin, an eminent surgeon in Penzance. Robert Davy and his wife became the parents of five children—two boys, Humphry, the eldest, and John, and three girls. In Davy's childhood the family moved from Penzance to Varfell, their family estate in Ludgvan. Davy's boyhood was spent partly with his parents and partly with Tonkin, who placed him at a preparatory school kept by a Mr. Bushell, who was so much struck with the boy's progress that he persuaded the father to send him to a better school. Davy was at an early age placed at the Penzance grammar school, then under the care of the Rev. J. C. Coryton. Numerous anecdotes show that Davy was a precocious boy, possessing a remarkable memory and being singularly rapid in acquiring knowledge of books. He was especially attracted by the ‘//Pilgrim's Progress//,’ and he delighted in reading history. When but eight years of age he would collect a number of boys, and standing on a cart in the market-place address them on the subject of his latest reading. He delighted in the folklore of this remote district, and became, as he himself tells us, a ‘tale-teller.’ The ‘applause of my companions,’ he says, ‘was my recompense for punishments incurred for being idle.’ These conditions developed a love of poetry and the composition of verses and ballads.

Discovery: Alkali metals. The alkali metals are all highly reactive and are never found in elemental form in nature. As a result, in the laboratory they are stored under [|mineral oil] or paraffin oil. They also tarnish easily and have low melting points and densities. Potassium and rubidium possess a weak radioactive characteristic due to the presence of long duration radioactive isotopes. The alkali metals are silver-colored (caesium has a golden tinge), soft, low-density metals, which react readily with halogens to form ionic salts, and with water to form strongly alkaline (basic) hydroxides. These elements all have one electron in their outermost shell, so the energetically preferred state of achieving a filled electron shell is to lose one electron to form a singly charged positive ion, i.e. cation. Hydrogen, with a solitary electron, is usually placed at the top of Group 1 of the periodic table, but it is not considered an alkali metal; rather it exists naturally as a diatomic gas. Removal of its single electron requires considerably more energy than removal of the outer electron for the alkali metals. As in the halogens, only one additional electron is required to fill in the outermost shell of the hydrogen atom, so hydrogen can in some circumstances behave like a halogen, forming the negative hydride ion. Binary compounds of hydride with the alkali metals and some transition metals have been prepared. Under extremely high pressure, such as is found at the core of Jupiter, hydrogen does become metallic and behaves like an alkali metal; see metallic hydrogen.

Name: John Dalton Date: 6 September 1766 – 27 July 1844 Country: England Year of Discovery: 1801 Biography: John Dalton was born into a Quaker family at Eaglesfield, near Cockermouth in Cumberland, England. The son of a weaver, he joined his older brother Jonathan at age 15 in running a Quaker school in nearby Kendal. Around 1790 Dalton seems to have considered taking up law or medicine, but his projects were not met with encouragement from his relatives — Dissenters were barred from attending or teaching at English universities — and he remained at Kendal until, in the spring of 1793, he moved to Manchester. Mainly through John Gough, a blind philosopher and polymath from whose informal instruction he owed much of his scientific knowledge, Dalton was appointed teacher of mathematics and natural philosophy at the "New College" in Manchester, a Dissenting academy. He remained in that position until 1800, when the college's worsening financial situation led him to resign his post and begin a new career in Manchester as a private tutor for mathematics and natural philosophy. Discovery: In chemistry and physics, **atomic theory** is a theory of the nature of matter, which states that matter is composed of discrete units called atoms, as opposed to the obsolete notion that matter could be divided into any arbitrarily small quantity. It began as a philosophical concept in ancient Greece and India and entered the scientific mainstream in the early 19th century when discoveries in the field of chemistry showed that matter did indeed behave as if it were made up of particles.
 * __1800-1875__
 * 1) John Dalton

2. Frederick Abel Name: Sir Frederick Augustus Abel Date: 17 July 1827 – 6 September 1902 Country: England Year of Discovery: around 1880 Biography: Sir Frederick Augustus Abel, 1st Baronet FRS ( 17 July 1827 – 6 September 1902 ) was an English chemist. (The Chambers Biographical Dictionary gives his year of birth as 1826.) Born in London, Abel studied chemistry for six years under A. W. von Hofmann at the Royal College of Chemistry, then became professor of chemistry at the Royal Military Academy, Woolwich 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 connection with the chemistry of explosives. One of the most important of his investigations had to do with the manufacture of guncotton, and he developed a process, consisting essentially of reducing the nitrated cotton to fine pulp, which enabled it to be safely manufactured and at the same time yielded the product in a form that increased its usefulness. Discovery: Cordite. **Cordite** is a family of smokeless propellants developed and produced in the United Kingdom to replace gunpowder as a military propellant. Like gunpowder, cordite is classified as a low explosive because of its slow burning rates and consequently low brisance. These produce a subsonic deflagration wave rather than the supersonic detonation wave produced by brisants, or high explosives. The hot gases produced by burning gunpowder or cordite generate sufficient pressure to propel a bullet or shell to its target, but not enough to destroy the barrel of the firearm, or gun.

3. Jons Jakob Berzelius Name: Friherre Jons Jacob Berzelius Date: 20 August 1779 – 7 August 1848 Country: Sweden Year of Discovery: 19th century Biography: Berzelius was born at Väversunda in Östergötland in Sweden. He lost both his parents at an early age. He was taken care of by relatives in Linköping where he attended the school today known as Katedralskolan. Thereafter he enrolled at the Uppsala University where he learned the profession of medical doctor from 1796 to 1801. He was taught chemistry by Anders Gustaf Ekeberg, the discoverer of tantalum. He worked as apprentice in a pharmacy and with a physician in the Medevi mineral springs. During this time he conducted analysis of the spring water. For his medical studies he examined the influence of galvanic current on several diseases. He worked as physician near Stockholm until the mine owner Wilhelm Hisinger discovered his analytical abilities and provided him with a laboratory. In 1807 Berzelius was appointed professor in chemistry and pharmacy at the Karolinska Institute. In 1808, he was elected a member of the Royal Swedish Academy of Sciences. At this time, the Academy had been stagnating for a number of years, since the era of romanticism in Sweden had led to less interest in the sciences. In 1818, Berzelius was elected the Academy's secretary, and held the post until 1848. During Berzelius' tenure, he is credited with revitalising the Academy and bringing it into a second golden era, the first being the astronomer Pehr Wilhelm Wargentin's period as secretary (1749-1783). In 1837, he was also elected a member of the Swedish Academy, on chair number 5. Discovery: Chemical Notation. A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound. The chemical formula identifies each constituent element by its chemical symbol and indicates the number of atoms of each element found in each discrete molecule of that compound. If a molecule contains more than one atom of a particular element, this quantity is indicated using a subscript after the chemical symbol (although 19th-century books often used superscripts). Chemical formulas may be used in chemical equations to describe chemical reactions. For ionic compounds and other non-molecular substances empirical formula may be used, in which the subscripts indicate the ratio of the elements. The 19th-century Swedish chemist Jöns Jakob Berzelius worked out this system for writing chemical formulas.

Name: Wilhelm Conrad Röntgen Date: 27 March 1845 – 10 February 1923 Country: Prussia - Germany Year of Discovery: 1895 Biography: Röntgen was born in Lennep (which is today a borough of Remscheid) in Rhenish Prussia as the only child of a merchant and manufacturer of cloth. His mother was Charlotte Constanze Frowein of Amsterdam. In March 1848, the family moved to Apeldoorn and Wilhelm was raised in the Netherlands. He received his early education at the private school of Martinus Herman van Doorn, in Apeldoorn. From 1861 to 1863, he attended the ambachtsschool in Utrecht. He was expelled for refusing to reveal the identity of a classmate guilty of drawing an unflattering portrait of one of the school's teachers. Not only was he expelled, he could not subsequently be admitted into any other Dutch or German gymnasium. Discovery: Discovery of X-rays. During 1895 Röntgen was investigating the external effects from the various types of vacuum tube equipment—apparatus from Heinrich Hertz, Johann Hittorf, William Crookes, Nikola Tesla and Philipp von Lenard—when an electrical discharge is passed through them. In early November he was repeating an experiment with one of Lenard's tubes in which a thin aluminium window had been added to permit the cathode rays to exit the tube but a cardboard covering was added to protect the aluminium from damage by the strong electrostatic field that is necessary to produce the cathode rays. He knew the cardboard covering prevented light from escaping, yet Röntgen observed that the invisible cathode rays caused a fluorescent effect on a small cardboard screen painted with barium platinocyanide when it was placed close to the aluminium window. It occurred to Röntgen that the Hittorf-Crookes tube, which had a much thicker glass wall than the Lenard tube, might also cause this fluorescent effect.
 * __1875-1900__
 * 1) Wilhelm C Roentgen

2. Marie Curie Name: Maire Sklodowska Curie Date: November 7, 1867 – July 4, 1934 Country: Russia - France Year of Discovery: 1898 Biography: Marie Skłodowska Curie was a physicist and chemist of Polish upbringing and, subsequently, French citizenship. She was a pioneer in the field of radioactivity, the first person honored with two Nobel Prizes, and the first female professor at the University of Paris. She was born Maria Skłodowska in Warsaw (then Vistula Country, Russian Empire; now Poland) and lived there until she was 24. In 1891 she followed her elder sister Bronisława to study in Paris, where she obtained her higher degrees and conducted her subsequent scientific work. She founded the Curie Institutes in Paris and Warsaw. Her husband Pierre Curie was a Nobel co-laureate of hers, and her daughter Irène Joliot-Curie and son-in-law Frédéric Joliot-Curie also received Nobel prizes. Her achievements include the creation of a theory of //radioactivity// (a term coined by her), techniques for isolating radioactive isotopes, and the discovery of two new elements, polonium and radium. It was also under her personal direction that the world's first studies were conducted into the treatment of neoplasms (cancers), using radioactive isotopes. While an actively loyal French citizen, she never lost her sense of Polish identity. She named the first new chemical element that she discovered (1898) polonium for her native country, and in 1932 she founded a Radium Institute (now the Maria Skłodowska–Curie Institute of Oncology) in her home town Warsaw, headed by her physician-sister Bronisława.

Discovery: Polonium. Also tentatively called "Radium F", polonium was discovered by Marie Skłodowska-Curie and her husband Pierre Curie in 1898 and was later named after Marie Curie's native land of Poland (Latin: //Polonia//)[17][18] Poland at the time was under Russian, Prussian, and Austrian partition, and did not exist as an independent country. It was Curie's hope that naming the element after her native land would publicize its lack of independence. Polonium may be the first element named to highlight a political controversy. This element was the first one discovered by the Curies while they were investigating the cause of pitchblende radioactivity. The pitchblende, after removal of the radioactive elements uranium and thorium, was more radioactive than both the uranium and thorium put together. This spurred the Curies on to find additional radioactive elements. The Curies first separated out polonium from the pitchblende, and then within a few years, also isolated radium.

3. Henri Becquerel Name: Antoine Henri Becquerel Date: 15 December 1852 – 25 August 1908 Country: France Year of Discovery: 1896 Biography: Becquerel was born in Paris into a family which produced four generations of scientists, including Becquerel's own son Jean. He studied science at the École Polytechnique and engineering at the École des Ponts et Chaussées. In 1890 he married Louise Désirée Lorieux. In 1892, he became the third in his family to occupy the physics chair at the Muséum National d'Histoire Naturelle. In 1894, he became chief engineer in the Department of Bridges and Highways. In 1896, while investigating phosphorescence in uranium salts, Becquerel accidentally discovered radioactivity. Investigating the work of Wilhelm Conrad Röntgen, 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.

Discovery: Radioactivity. Radioactivity was first discovered in 1896 by the French scientist Henri Becquerel, while working on phosphorescent materials. These materials glow in the dark after exposure to light, and he thought that the glow produced in cathode ray tubes by X-rays might be connected with phosphorescence. He wrapped a photographic plate in black paper and placed various phosphorescent salts on it. All results were negative until he used uranium salts. The result with these compounds was a deep blackening of the plate. These radiations were called Becquerel Rays. It soon became clear that the blackening of the plate had nothing to do with phosphorescence, because the plate blackened when the mineral was in the dark. Non-phosphorescent salts of uranium and metallic uranium also blackened the plate. Clearly there was a form of radiation that could pass through paper that was causing the plate to become black. At first it seemed that the new radiation was similar to the then recently discovered X-rays. Further research by Becquerel, Marie Curie, Pierre Curie, Ernest Rutherford and others discovered that radioactivity was significantly more complicated. Different types of decay can occur, but Rutherford was the first to realize that they all occur with the same mathematical approximately exponential formula (see below). The early researchers also discovered that many other chemical elements besides uranium have radioactive isotopes. A systematic search for the total radioactivity in uranium ores also guided Marie Curie to isolate a new element polonium and to separate a new element radium from barium. The two elements' chemical similarity would otherwise have made them difficult to distinguish.

4. J. J. Thomson Name: Sir Joseph John "J.J." Thomson Date: 18 December 1856 – 30 August 1940 Country: England Year of Discovery: 1897 Biography: Joseph John Thomson was born in 1856 in Cheetham Hill, Manchester in England, of Scottish parentage. His father died when he was 16 years old. In 1870 he studied engineering at University of Manchester known as Owens College at that time, and moved on to Trinity College, Cambridge in 1876. In 1880, he obtained his BA in mathematics (Second Wrangler and 2nd Smith's prize) and MA (with Adams Prize) in 1883.[2] In 1884 he became Cavendish Professor of Physics. One of his students was Ernest Rutherford, who would later succeed him in the post. In 1890 he married Rose Elisabeth Paget, daughter of Sir George Edward Paget, KCB, a physician and then Regius Professor of Physic at Cambridge. He fathered one son, George Paget Thomson, and one daughter, Joan Paget Thomson, with her. One of Thomson's greatest contributions to modern science was in his role as a highly gifted teacher, as seven of his research assistants and his aforementioned son won Nobel Prizes in physics. His son won the Nobel Prize in 1937 for proving the wavelike properties of electrons. He was awarded a Nobel Prize in 1906, "in recognition of the great merits of his theoretical and experimental investigations on the conduction of electricity by gases." He was knighted in 1908 and appointed to the Order of Merit in 1912. In 1914 he gave the Romanes Lecture in Oxford on "The atomic theory". In 1918 he became Master of Trinity College, Cambridge, where he remained until his death. He died on 30 August 1940 and was buried in Westminster Abbey, close to Sir Isaac Newton. Thomson was elected a Fellow of the Royal Society on 12 June 1884 and was subsequently President of the Royal Society from 1915 to 1920.

Discovery: 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) 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. The model was disproved by the 1909 gold foil experiment, which was interpreted by Ernest Rutherford in 1911 to imply a very small nucleus of the atom containing a very high positive charge (enough to balance about 100 electrons in gold), thus leading to the Rutherford model of the atom. Finally, after Henry Moseley's work showed in 1913 that the nuclear charge was very close to the atomic number, Antonius Van den Broek suggested that atomic number is nuclear charge. This work had culminated in the solar-system-like (but quantum-limited) Bohr model of the atom in the same year, in which a nucleus containing an atomic number of positive charge is surrounded by an equal number of electrons in orbital shells.

Name: Ernest Rutherford Date: 30 August 1871 - 19 October 1937 Country: New Zealand - England Year of Discovery: 1911 Biography: Discovery: Rutherford model. The **Rutherford model** or **planetary model** is a model of the atom devised by Ernest Rutherford. Rutherford directed the famous Geiger-Marsden experiment in 1909, which suggested to Rutherford's analysis (1911) that the Plum pudding model of J. J. Thomson of the atom was incorrect. Rutherford's new model for the atom, based on the experimental results, had a number of essential modern features, including a relatively high central charge concentrated into a very small volume in comparison to the rest of the atom and containing the bulk of the atomic mass (the nucleus of the atom), and a number of tiny electrons circling around the nucleus like planets around the sun.
 * __1900-1915__
 * 1) Ernest Rutherford
 * Ernest Rutherford, 1st Baron Rutherford of Nelson**, was a New Zealand chemist and physicist who became known as the father of nuclear physics. 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 scattering 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.

2. Robert Millikan Name: Robert Andrews Millikan Date: 22 March 1868 – 19 December 1953 Country: United States Year of Discovery: 1913 Biography: Millikan went to high school in Maquoketa, Iowa. Millikan received a Bachelor's degree in the classics from Oberlin College in 1891 and his doctorate in physics from Columbia University in 1895 – he was the first to earn a Ph.D. from that department. Millikan's enthusiasm for education continued throughout his career, and he was the coauthor of a popular and influential series of introductory textbooks, which were ahead of their time in many ways. Compared to other books of the time, they treated the subject more in the way in which it was thought about by physicists. They also included many homework problems that asked conceptual questions, rather than simply requiring the student to plug numbers into a formula. In 1902 he married Greta Ervin Blanchard. They had three sons - Clark Blanchard, Glenn Allen, and Max Franklin. Discovery: Charge of Electron. Starting in 1909, while a professor at the University of Chicago, Millikan and Harvey Fletcher worked on an oil-drop experiment (since repeated, with varying degrees of success, by generations of physics students) in which they measured the charge on a single electron. Professor Millikan took sole credit, in return for Fletcher claiming full authorship on a related result for his dissertation. Millikan went on to win the 1923 Nobel Prize for Physics, in part for this work, and Fletcher kept the agreement a secret until his death. After a publication on his first results in 1910, contradictory observations by Felix Ehrenhaft started a controversy between the two physicists. After improving his setup he published his seminal study in 1913. The elementary charge is one of the fundamental physical constants and accurate knowledge of its value is of great importance. His experiment measured the force on tiny charged droplets of oil suspended against gravity between two metal electrodes. Knowing the electric field, the charge on the droplet could be determined. Repeating the experiment for many droplets, Millikan showed that the results could be explained as integer multiples of a common value (1.592 × 10−19 coulomb), the charge on a single electron. That this is somewhat lower than the modern value of 1.602 176 53(14) x 10−19 coulomb is probably due to Millikan's use of an inaccurate value for the viscosity of air.
 * Robert A. Millikan** was an American experimental physicist, and Nobel laureate in physics for his measurement of the charge on the electron and for his work on the photoelectric effect. He served as president of Caltech from 1921 to 1945.

3. Niels Bohr: Name: Niels Henrik David Bohr Date of birth-death: 7/10/1885 - 18/11/1962 Country: Denmark Year of Discovery: 1913 Biography: Discovery: On the basis of Rutherford's theories, Bohr published his model of atomic structure in 1913, introducing the theory of electrons traveling in orbits around the atom's nucleus, the chemical properties of the element being largely determined by the number of electrons in the outer orbits. Bohr also introduced the idea that an electron could drop from a higher-energy orbit to a lower one, emitting a photon (light quantum) of discrete energy. This became a basis for quantum theory.
 * Niels Henrik David Bohr** ( 7 October 1885 – 18 November 1962) was a Danish physicist who made fundamental contributions to understanding atomic structure and quantum mechanics, for which he received the Nobel Prize in Physics in 1922. Bohr mentored and collaborated with many of the top physicists of the century at his institute in Copenhagen. He was part of a team of physicists working on the Manhattan Project. Bohr married Margrethe Nørlund in 1912, and one of their sons, Aage Niels Bohr, grew up to be an important physicist who in 1975 also received the Nobel prize. Bohr has been described as one of the most influential physicists of the 20th century.

Name: Ernest Rutherford Date: 30 August 1871 - 19 October 1937 New Zealand - England Year of Discovery: 1919 Biography: (Already written above) Discovery: Proton. The **proton** is a subatomic particle with an electric charge of +1 elementary charge. It is found in the nucleus of each atom but is also stable by itself and has a second identity as the hydrogen ion, H+. It is composed of three fundamental particles: two up quarks and one down quark. Protons are spin-½ fermions and are composed of three quarks, making them baryons. The two up quarks and one down quark of the proton are held together by the strong force, mediated by gluons. Protons are spin-½ fermions and are composed of three quarks, making them baryons. The two up quarks and one down quark of the proton are held together by the strong force, mediated by gluons. Protons and neutrons are both nucleons, which may be bound by the nuclear force into atomic nuclei. The nucleus of the most common isotope of the hydrogen atom is a single proton (it contains no neutrons). The nuclei of heavy hydrogen (deuterium and tritium) contain neutrons. All other types of atoms are composed of two or more protons and various numbers of neutrons. The number of protons in the nucleus determines the chemical properties of the atom and thus which chemical element is represented; it is the number of both neutrons and protons in a nuclide which determine the particular isotope of an element. Protons have a +1 charge. This is the same magnitude of an electron but an electron has a −1 charge.
 * __1915 - 1950__
 * 1) Ernest Rutherford

2. James Chadwick Name: Sir James Chadwick Date: 20 October 1891 – 24 July 1974 Country: England Year of Discovery: 1932 Biogrpahy: Chadwick was born in Bollington, Cheshire to John Joseph Chadwick and Annie Mary //née// Knowles. He went to Bollington Cross C of E Primary School, attended the Central Grammar School for Boys in Manchester, and then studied at the Universities of Manchester and Cambridge. In 1913 Chadwick went and worked with Hans Geiger at the Technical University of Berlin. He also worked with Ernest Rutherford. He was in Germany at the start of World War I and was interned in Ruhleben P.O.W. Camp just outside Berlin. During his internship he had the freedom to set up a laboratory in the stables. With the help of Charles Ellis he worked on the ionization of phosphorus and also on the photo-chemical reaction of carbon monoxide and magnesium. He spent most of the war years in Ruhleben until Geiger's laboratory interceded for his release. Discovery: Neutron. The **neutron** is a subatomic particle with no net electric charge and a mass slightly larger than that of a proton. Neutrons are usually found in atomic nuclei. The nuclei of most atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of protons in a nucleus is the atomic number and defines the type of element the atom forms. The number of neutrons is the neutron number and determines the isotope of an element. For example, the carbon-12 isotope has 6 protons and 6 neutrons, while the carbon-14 isotope has 6 protons and 8 neutrons. While bound neutrons in stable nuclei are stable, free neutrons are unstable; they undergo beta decay with a lifetime of just under 15 minutes (885.7 ± 0.8 s). Free neutrons are produced in nuclear fission and fusion. Dedicated neutron sources like research reactors and spallation sources produce free neutrons for the use in irradiation and in neutron scattering experiments. Even though it is not a chemical element, the free neutron is sometimes included in tables of nuclides. It is then considered to have an atomic number of zero and a mass number of one.
 * Sir James Chadwick**, was an English Nobel laureate in physics awarded for his discovery of the neutron.

3. Erwin Schrodinger Name: Erwin Rudolf Josef Alexander Schrödinger Date: 12 August, 1887– 4 January 1961 Country: Austria Year of Discovery: 1926 Biography: In 1887 Schrödinger was born in Vienna, Austria to **Rudolf Schrödinger** (cerecloth producer, botanist) and **Georgine Emilia Brenda** (daughter of **Alexander Bauer**, Professor of Chemistry, k.u.k. Technische Hochschule Vienna). His mother was half Austrian and half English; the English side of her family came from Leamington Spa. Schrödinger learned English and German almost at the same time due to the fact that both were spoken in the family household. His father was a Catholic and his mother was a Lutheran. In 1898 he attended the Akademisches Gymnasium. Between 1906 and 1910 Schrödinger studied in Vienna under Franz Serafin Exner (1849 - 1926) and Friedrich Hasenöhrl (1874 - 1915). He also conducted experimental work with K.W.F. Kohlrausch. In 1911, Schrödinger became an assistant to Exner. At an early age, Schrödinger was strongly influenced by Schopenhauer. As a result of his extensive reading of Schopenhauer's works, he became deeply interested throughout his life in color theory, philosophy, perception, and eastern religion, especially Vedanta.

Discovery: Schrödinger equation. In physics, specifically quantum mechanics, the **Schrödinger equation** is an equation that describes how the quantum state of a physical system changes in time. It is as central to quantum mechanics as Newton's laws are to classical mechanics. In the standard interpretation of quantum mechanics, the quantum state, also called a wavefunction or state vector, is the most complete description that can be given to a physical system. Solutions to Schrödinger's equation describe not only atomic and subatomic systems, atoms and electrons, but also macroscopic systems, possibly even the whole universe. The equation is named after Erwin Schrödinger, who constructed it in 1926. Schrödinger's equation can be mathematically transformed into Heisenberg's matrix mechanics, and into Feynman's path integral formulation. The Schrödinger equation describes time in a way that is inconvenient for relativistic theories, a problem which is not as severe in Heisenberg's formulation and completely absent in the path integral.

4. Werner Heisenberg Name: Werner Heisenberg Date: 5 December 1901 – 1 February 1976 Country: Germany Year of Discovery: 1925 Biography: Werner Heisenberg was a German theoretical physicist who made foundational contributions to quantum mechanics and is best known for asserting the uncertainty principle of quantum theory. In addition, he also made important contributions to nuclear physics, quantum field theory, and particle physics. Heisenberg, along with Max Born and Pascual Jordan, set forth the matrix formulation of quantum mechanics in 1925. Heisenberg was awarded the 1932 Nobel Prize in Physics. The German nuclear energy project, also known informally as the Uranium Club, began in 1939 under the auspices of the German Ordnance Office. In 1942, control of the project was relinquished to the Reich Research Council. Throughout the project, Heisenberg was one of the nine principals heading up research and development for the program. In 1942, Heisenberg was appointed as director-in-residence of the Kaiser Wilhelm Institute for Physics. Heisenberg was one of 10 German scientists arrested near the end of World War II under the American Operation Alsos. He was detained in England from May 1945 to January 1946. Upon Heisenberg's return to Germany, he settled in Göttingen in the British occupation zone, where he was appointed director of the Kaiser Wilhelm Institute for Physics, which was soon thereafter renamed the Max Planck Institute for Physics. He was director of the institute until it was moved to Munich in 1958, when it was expanded and renamed the Max Planck Institute for Physics and Astrophysics. For two years, he was co-director with the astrophysicist Ludwig Biermann. Heisenberg was director of the institute from 1960 to 1970. Heisenberg was also president of the German Research Council, chairman of the Commission for Atomic Physics, chairman of the Nuclear Physics Working Group, and president of the Alexander von Humboldt Foundation. In 1957, Heisenberg was a signatory of the Göttingen Manifesto, a declaration of 18 leading nuclear scientists of West Germany against arming the West German army with tactical nuclear weapons.

Discovery: Uncertainty Principle. In quantum mechanics, the Heisenberg uncertainty principle states that certain pairs of physical properties, like position and momentum, cannot both be known to arbitrary precision. That is, the more precisely one property is known, the less precisely the other can be known. This is not a statement about the limitations of a researcher's ability to measure particular quantities of a system, it is a statement about the nature of the system itself as described by the equations of quantum mechanics. According to the uncertainty principle, it is, for instance, impossible to measure simultaneously both position and velocity of a microscopic particle with any degree of accuracy or certainty. In quantum mechanics, a particle is described by a wave. The position of the particle is regarded as being where the wave amplitude is greatest and the momentum is determined by the wavelength. The position is uncertain to the degree that the wave is spread out (well-defined wavelength), //but// the momentum is certain (well-defined) only to the degree that the wavelength is well-defined. Thus, position and momentum for a particle have opposite requirements for good definition, so that both position and wavelength cannot simultaneously be well-defined.

Dalton's theory was based on the premise that the atoms of different elements could be distinguished by differences in their weights. He stated his theory in a lecture to the Royal Institution in 1803. The theory proposed a number of basic ideas:
 * Dalton's model
 * Atomic theory proposed by John Dalton[[image:http://www.ngdir.ir/SiteLinks/Kids/Image/energy_image_fa/atom_model_03_FF.gif width="279" height="210" align="right"]]**

All matter is composed of atoms Atoms cannot be made or destroyed All atoms of the same element are identical Different elements have different types of atoms Chemical reactions occur when atoms are rearranged Compounds are formed from atoms of the constituent elements.

The design was proposed by J.J. Thomson in 1906. The discovery of the nucleus had yet to be made, so naturally this component of the atom was lacking from Thompsons model. What he did include, however were “corpuscles,” Thompsons name for electrons, that he depicted as plums in his model. The pudding was a positively charged area of mass which balanced out the negative charge of his plum-like “corpuscles”.
 * Plum pudding Model


 * Rutherford-Bohr Model[[image:http://www.epa.gov/rpdweb00/images/ruthbohr.jpg align="right"]]

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



Developed by Neils Bohr, in his model the protons and neutrons are located in the small, dense nucleus, while the electrons orbit around them. The scale is disproportionate, however, because of the fact that the atomic radius is roughly 1000 times that of the nucleus.

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
 * Bohr's Model

Based upon the work of a number of scientists including Rutherford, Bohr, Heisenberg and Schrödinger, the Electron Cloud Model is a compilation of ideas. Rutherford's contribution is the small dense nucleus within a cloud. The electron cloud surrounding it is made up by ideas form Bohr and Heisenberg. Bohr had the idea that electrons moved around the nucleus while Heisenberg figured out that the only way to describe where they are is through probity distribution. His concept is involved in quantum mechanics where Schrödinger comes into play. The electron cloud is a region were the electrons could be found but doesn’t specify where they are.
 * Electron Cloud Model[[image:http://honolulu.hawaii.edu/distance/sci122/Programs/p28/p282.gif width="287" height="184" align="right"]]