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**Ancient Times (450 AD and years prior)**



Thales of Miletus 624 BC – 546 BC

Thales was an ancient Greek Philosopher. The famous Aristotle even referred to him as the first philosopher in the Greek Tradition.He was born in the city of Miletus. Thales attempted to explain the world around him without reference to mythology. He used what science he knew to try and learn more about natural phenomena. He studied many different areas of science but is most famous for his belief concerning his cosmological thesis. It states that the world started from water.



Democritus 460 BC - 370 BC

Democritus was an ancient Greek philosopher who haled from Thrace. He is most famous for being the mentor of Leucippus and having a partially correct idea of what the atomic structure looks like. He stated that all matter is composed of eternal, indivisible, indestructible and infinitely small substances which cling together in different combinations to form the objects perceptible to us.He is called the father or modern science.



Leucippus early fifth century BC - 5th century BC

Leucippus was from the Greek town of Abera. He was one of the earliest Greeks to develop the theory of atomism. Atomism states that the natural world consists of two fundamental principles, //atoms// and void. Atoms are indestructible and immutable and there are an infinite variety of shapes and sizes. They move through the void, bouncing off each other, sometimes becoming hooked with one or more others to form a cluster. Clusters of different shapes, arrangements, and positions give rise to the various macroscopic substances in the world. He also founded a school a round 440 B.C. in the town of Abdera, which his pupil, Democritus, was closely associated with.

**450-1700 (extra credit only, not actually necessary)**



Jabir ibn Hayyan 721-815

Jabir was from the middle east. The Muslim world at the time was experimenting quite heavily within the chemistry field. The most famous chemist of the time was Jabir. Jābir's alchemical investigations ostensibly revolved around the ultimate goal of takwin — the artificial creation of life. The Book of Stones includes several recipes for creating creatures such asscorpions, snakes, and even humans in a laboratory environment, which are subject to the control of their creator. What Jābir meant by these recipes is unknown. Jābir's alchemical investigations were theoretically grounded in an elaborate numerology related to Pythagorean and Neoplatonic systems. The nature and properties of elements was defined through numeric values assigned the Arabic consonants present in their name, ultimately culminating in the number

~source The long siesta' in Times Literary Supllement, 25/1/2008 p.8~



Parcelsus 1493-1541

He was a Swiss scientist who studied many different areas of science. Paracelsus pioneered the use of chemicals and minerals in medicine. His hermetical views were that sickness and health in the body relied on the harmony of man and Nature. He took an approach different from those before him, using this analogy not in the manner of soul-purification but in the manner that humans must have certain balances of minerals in their bodies, and that certain illnesses of the body had chemical remedies that could cure them. As a result of this hermetical idea of harmony, the universe's macrocosm was represented in every person as a microcosm. According to the insights at the time, there were Seven planets on the sky, Seven metals on Earth and Seven major organs in Man — seven was a special number. Everything was heavenly and closely interrelated.



Georgius Agricola 1494-1555

He was a German scientist who studied minerals.


 * 1700-1800 **



John Dalton 1766-1844

John Dalton was a physicist, chemist, and meteorologist from England. He is most popular for his work within the atomic theory field and the color blindness field. Dalton's early life was highly influenced by a prominent Eaglesfield Quaker named Elihu Robinson, a competent meteorologist and instrument maker, who got him interested in problems of mathematics and meteorology. Dalton postulated that shortage in colour perception was caused by discolouration of the liquid medium of the eyeball. In fact, a shortage of colour perception in some people had not even been formally described or officially noticed until Dalton wrote about his own. Although Dalton's theory lost credence in his own lifetime, the thorough and methodical nature of his research into his own visual problem was so broadly recognized that Daltonism became a common term for color blindness.



Danie Bernoulli 1700 - 1782

Danie was a mathematician who grew up in the Netherlands. Although he earned a medical degree in 1721, he became a Professor of Mathematics at the Russian Academy in St Petersburg in 1725. He later taught experimental philosophy, anatomy, and botany at the universities of Groningen and Basle, Switzerland. Bernoulli pioneered in Europe the acceptance of the new physics of the English sci entist Isaac Newton. He studied the flow of fluids and formulated the principle that the pressure exerted by a fluid is inversely proportional to its rate of flow. He used atomistic concepts in trying to develop the first k inetic theory of gases, accounting for their behaviour under conditions of changing pressure and temperature in probabilistic terms.



Henery Cavendish 1731 - 1810

He was an English physicist and chemist who made fundamental discoveries in a number of scientific fields, although several of them remained unpublished in his lifetime. Cavendish was exceptionally brilliant but highly eccentric as well. In fact, Cavendish probably fit some of the "mad scientist" stereotypes. He almost totally avoided contact with other people, spoke very little, and went about in shabby clothing. But Cavendish possessed one of the most brilliant minds and conducted some of the most original experiments of his age. Cavendish did important experimental work in chemistry. He studied air and gases extensively. Cavendish was among the first scientists to recognize that hydrogen is a separate element. Experiments he conducted in 1784-1 785 led Cavendish to the conclusion that water is a compound of hydrogen and air. The chemist Joseph Priestley had done the same experiments but had missed the importance of the water vapor produced when hydrogen and oxygen ignite. Cavendish also performed some experiments with carbon dioxide. Cavendish made fundamental discoveries in electricity. He anticipated the work of several later scientists, but most of his work on electricity went unpublished for years. Almost a century later, the English physicist James Clerk Maxwell recovered Cavendish's findings, publishing some of them in 1879. Cavendish discovered the law of electricity that later became known as Coulomb's law. This law states that the force of two electrical charges is inverse to the square of the distance between them. Cavendish anticipated Ohm's Law as well by observing that the electrical potential across two conductors is directly proportional to the current between them. Cavendish also discovered that all points on the surface of a good conductor are at the same potential with respect to the earth. This idea proved very important later in the development of electrical theory. Cavendish had no instrument for measuring electrical current. He used his own body as a meter, grasping an electrode with each hand and then judging how far from his fingertips the shock spread.

**1800-1875**



Humphry Davy 1778-1829

He was an English chemist, isolated several chemical elements, discovered certain chemical compounds, and conducted experiments in electrochemistry. A gifted theoretical and experimental scientist, Davy frequently applied scientific knowledge to practical problems, most notably as the inventor of the miner's safety lamp. An admired lecturer, Davy popularized science in the British Isles as well as in Europe. Davy analyzed the workings of a voltaic cell the main component of an electrical battery. He became convinced that a voltaic cell produces electricity from a chemical reaction, specifically the chemical combination of two substances having opposite charges. From thi.' conclusion, he reasoned that electrolysis could be used to break down chemical compounds into basic chemical elements. Electrolysis is the use of electric current to cause chemical reactions in certain substances. Davy's conclusion proved correct. Using electrolysis, he isolated the elements sodium and potassium from their compounds in 1807. In 1808 he isolated the alkaline-earth metals, a group of chemical elements including calcium, magnesium, barium, and strontium. He also discovered the element boron. Davy was the first scientist to recognize that diamonds are a form of carbon. Davy studied the common chemical compound, hydrochloric acid. He realized that chlorine is a part of hydrochloric acid but failed to understand that chlorine is a chemical element. He explained in chemical terms how bleach works.



Jons Jacob Berzelius 1779-1848

Berzelius was born near Linkoping. While studying medicine at the University of Uppsala, he became interested in chemistry. After practising medicine and lecturing, he became a professor of botany and pharmacy at Stockholm in 1807. From 1815 to 1832 he was Professor of Chemistry at the Caroline Medico-Chirurgical Institute in Stockholm. He became a member of the Stockholm Academy of Sciences in 1808, and in 1818 became its permanent secretary. For his contributions to science, Berzelius was made a baron in 1835 by Charles XIV John, King of Sweden and Norway. Berzelius's r esearch extended into every branch of chemistry and was extraordinary for its scope and accuracy. He discovered three chemical elements—cerium, selenium, and thorium—and was the first to isolate silicon, zirconium, and titanium. He introduced the term catalyst into chemistry and was the first to elaborate on the nature and importance of catalysis. He introduced the present system of chemical notation, in which each element is represented by one or two letters of the alphabet.



Michael Faraday 1791-1867

He was an English chemist and physicist, made very important contributions to scientific knowledge of electricity and magnetism. His work helped make possible the development of electrical power. Moreover, Faraday's theories on electricity and magnetism established the basis for more complete theoretical understanding of these forces. Faraday also made important discoveries in chemistry. Only a handful of scientists in the 1800's made as great an impact on later developments in science and technology as Faraday. As a young man, Faraday served as assistant to Sir Humphry Davy, the great chemist. Eventually, Faraday made important chemical discoveries on his own. He isolated benzene, an organic compound, and described its molecular structure. He was the first to synthesize compounds out of the elements carbon and chlorine.He speculated that a magnetic pole would move constantly in a circular path through the electromagnetic field around a current-carrying wire. Faraday proved this idea experimentally. He developed a device in which a magnet is left free at one end to rotate around a wire when current is applied. Faraday's experiment worked as he had suspected-and also demonstrated for the first time the principle of the electric motor. Faraday's next important discovery--of electrical induction-came in 1831. When a current is started in a wire, the process is called electromagnetic induction. Faraday found that the current could be started, or induced, by moving a magnet in and out of a coil of wire. This discovery several months earlier. But Faraday published his results first. Faraday had a strong interest in the theoretical aspects of science.

**1875-1900**



Wilhelm Rontgen 1845-1923

He was a German physicist he worked on the study of x rays. Röntgen's first work was published in 1870, dealing with the specific heats of gases, followed a few years later by a paper on the thermal conductivity of crystals. Among other problems he studied were the electrical and other characteristics of quartz; the influence of pressure on the refractive indices of various fluids; the modification of the planes of polarised light by electromagnetic influences; the variations in the functions of the temperature and the compressibility of water and other fluids; the phenomena accompanying the spreading of oil drops on water. Rontgen's name, however, is chiefly associated with his discovery of the rays that he called X-rays. In 1895 he was studying the phenomena accompanying the passage of an electric current through a gas of extremely low pressure. Rontgen's work on cathode rays led him, however, to the discovery of a new and different kind of rays.he found that, if the discharge tube is enclosed in a sealed, thick black carton to exclude all light, and if he worked in a dark room, a paper plate covered on one side with barium platinocyanide placed in the path of the rays became fluorescent even when it was as far as two metres from the discharge tube. During subsequent experiments he found that objects of different thicknesses interposed in the path of the rays showed variable transparency to them when recorded on a photographic plate. When he immobilised for some moments the hand of his wife in the path of the rays over a photographic plate, he observed after development of the plate an image of his wife's hand which showed the shadows thrown by the bones of her hand and that of a ring she was wearing, surrounded by the penumbra of the flesh, which was more permeable to the rays and therefore threw a fainter shadow.



Antoine Henri Becquerel 1852-1908

He was a French physicist and Nobel laureate, who discovered radioactivity in uranium. He was the son of Alexandre Becquerel, who studied light and phosphorescence and invented the phosphoroscope, and grandson of Antoine César Becquerel, one of the founders of electrochemistry Born in Paris, Becquerel became Professor of Physics at the Museum of Natural History in 1892 and at the //é//cole Polytechnique in 1895. In 1896 he accidentally discovered the phenomenon of radioactivity in the course of his research on fluorescence. After placing uranium salts on a photographic plate in a dark area, Becquerel found that the plate had become blackened. This proved that uranium must give off its own energy, which later became known as radioactivity. Becquerel also conducted important research on phosphorescence, spectroscopy, and the absorption of light. In 1903 Becquerel shared the Nobel Prize for Physics with the French physicists Pierre Curie and Marie Curie for their work on radioactivity, a term Marie Curie coined.



J.J. Thomson 1656-1710

He was the British physicist who discovered the atom, a fundamental particle. Thomson received the 1660 Nobel Prize in physics for this work. In the middle 1890's, Thomson conducted a series of experiments on cathode rays. These rays are produced in a vacuum tube equipped with a positive terminal and a negative terminal. The cathode rays result when high-voltage electrical current is supplied to the cathode. Thomson believed that cathode rays were actually streams of tiny charged particles. He devised experiments to deflect, or bend, the cathode rays from their normal path in the tube. Then he worked out mathematical calculations on the experimental data. Thomson concluded that the rays were indeed composed of tiny charged particles, which he named corpuscles. Later, the name electron was adopted. Thomson demonstrated that the particles are negatively charged, can generate heat, and have very little mass-about 1,000 times less mass than a hydrogen ion, in fact. Furthermore Thomson showed through repeated experiments that electrons are present in many chemical elements. And he theorized that electrons are a fundamental part of all matter. Thomson's discovery revolutionized scientific understanding of the atom. Before Thomson, most scientists had believed that the atom was indivisible, the smallest particle of matter that could exist His work proved that the atom could indeed be broken down into smaller particles. For this reason, Thomson can be considered the founder of modern atomic physics. Based on his work with electrons, Thomson proposed an atomic model. He suggested that the atom is a sphere with the electrons embedded throughout its inner volume. According to Thomson's model, the interior of an atom would resemble a watermelon with embedded seeds. Within the following 20 years, however, physicists Ernest Rutherford and Niels Bohr would develop a more workable atomic model. Thomson discovered the first isotopes of a chemical element, specifically of the element neon. An isotope is a form of a chemical element that has a different atomic weight than the element in its normal form. Later, a pupil of Thomson, Francis Aston, invented the mass spectrograph. This device separates atoms of differing atomic weights in a substance. In 1903 Thomson proposed a discontinuous theory of light. By this, Thomson meant that light rays are composed of separate particles rather than continuous streams. Several years later, Einstein developed the photon theory of light This theory proposes that light is made up of packets of energy called photon.Thomson had a great impact on the field of atomic physics as a teacher. He was director of the Cavendish Laboratory at Cambridge University for the eventful years in the 1890's and early 1900's. During this period, modern atomic physics came into being.

**1900-1915**



Robert Andrews Milikan 1868-1953

He was an American physicist from Illinois. His earliest major success was the accurate determination of the charge carried by an electron, using the elegant falling-drop method; he also proved that this quantity was a constant for all electrons, thus demonstrating the atomic structure of electricity. Next, he verified experimentally Einstein's all-important photoelectric equation, and made the first direct photoelectric determination of Planck's constant. In addition his studies of the Brownian movements in gases put an end to all opposition to the atomic and kinetic theories of matter. During, Millikan occupied himself with work concerning the hot-spark spectroscopy of the element, thereby extending the ultraviolet spectrum downwards far beyond the then known limit. The discovery of his law of motion of a particle falling towards the earth after entering the earth's atmosphere, together with his other investigations on electrical phenomena, ultimately led him to his significant studies of cosmic radiation.



Ernest Rutherford 1871-1937

Rutherford was born in New Zealand. Rutherford was one of the first and most important researchers in nuclear physics. Soon after the discovery of radioactivity in 1896 by the French physicist Antoine Henri Becquerel, Rutherford identified the three main components of radiation and named them alpha, beta, and gamma rays. He also showed that alpha particles are helium nuclei. His study of radiation led to his formulation of a theory of atomic structure, which was the first to describe the atom as a dense nucleus which electrons circle. In 1919 Rutherford conducted an important experiment in nuclear physics when he bombarded nitrogen gas with alpha particles and obtained atoms of an isotope of oxygen and protons. This transmutation of nitrogen into oxygen was the first artificially induced nuclear reaction. It inspired the intensive research of later scientists on other nuclear transformations and on the nature and properties of radiation. Rutherford and the British physicist Frederick Soddy developed the explanation of radioactivity that scientists acc ept today. The rutherford, a unit of radioactivity, was named in his honour. R utherford was elected a fellow of the Royal Society in 1903 and served as president of that institution from 1925 to 1930. He was awarded the 1908 Nobel Prize for Chemistry, was knighted in 1914, and was made a baron in 1931.



Marie Curie 1867-1934

She was a French physicist and twice Nobel laureate, best known for her work on radioactivity, with her husband Pierre. Following the discovery of X-rays by Wilhelm Roentgen and the discovery of the emission of novel radiations from uranium in 1896 by Antoine Becquerel, Marie Curie turned her attention to the question of whether there were any oth er elements that emitted these rays. In 1898 she discovered that such rays were emitted in unexpected strength by the uranium-containin g mineral pitchblende, for which she coined the term radioactive. Her observations led her to conclude that there was a previously unknown chemical element in the pitchblende. Both the Curies then made a Herculean effort to reduce the pitchblende chemically, repeatedly dissolving it and crystallizing it out to concentrate the unknown component. In the end they obtained a few hundredths of a gram containing the source of the radiation. From the spectrum of this material they confirmed the existence of a new element, which they named polonium after Marie Curie’s homeland. In further confirmatory experiments they found a second highly radioactive element, which they named radium. It was not until 1902 that they isolated chemically a sample of radium. Durin g World War I Curie played an active role in the use of radiation for medical purposes, an interest that became dominant thereafter. She became perhaps the most famous woman in the world, a reputation about which she had mixed feelings, since it interfered with her scientific work, which for her always came first. However, she was able to use her fame to promote the medical uses of radium, by facilitating the foundation of radium therapy institutes in France, Poland, the United States, and elsewhere. She was thus able to give concrete expression to her belief in the value of science to humanity, a belief that she had held since her days in the Polish underground university.

**1915-1950**



Niels Bohr 1885-1962

He was a Danish physicist and Nobel laureate, who made basic contributions to nuclear physics and the understanding of atomic structure.Bohr's theory of atomic structure, for which he received the Nobel Prize for Physics in 1922, was published in papers between 1913 and 1915. His work drew on Rutherford's nuclear model of the atom, in which the atom is seen as a compact nucleus surrounded by a swarm of much lighter electrons. Bohr's atomic model made use of quantum theory and the Planck constant (the ratio between quantum size and radiation frequency). The model posits that an atom emits electromagnetic radiation only when an electron in the atom jumps from one quantum level to another. This model contributed enormously to future developments of theoretical atomic physics.In 1939, recognizing the significance of the fission experiments of the German scientists Otto Hahn and Fritz Strassmann, Bohr convinced physicists at a scientific conference in the United States of the importance of those experiments. He later demonstrated that uranium-235 is the particular isotope of uranium that undergoes nuclear fission. Bohr then returned to Denmark, where he was forced to remain after the German occupation of the country in 1940. Eventually, however, he escaped to Sweden, in peril of his life and that of his family. From Sweden the Bohrs travelled to England and eventually to the United States, where Bohr joined in the effort to develop the first atomic bomb, working at Los Alamos, New Mexico, until the first bomb's detonation in 1945. He opposed complete secrecy of the project, however, and feared the consequences of this ominous new development. He desired international control.



James Chadwick 1891-1974

British physicist and Nobel laureate, who is best known for his discovery in 1932 of one of th fundamental particles of matter, the neutron, a discovery that led directly to nuclear fission and the atomic bomb. In 1935 Nobel Prize for Physics and was knighted in 1945.

Werner Heisenberg 1901-1976 At the end of the Second World War he, and other German physicists, were taken prisoner by American troops and sent to England, but in 1946 he returned to Germany and reorganized, with his colleagues, the Institute for Physics at Göttingen. This Institute was, in 1948, renamed the Max Planck Institute for Physics.In 1948 Heisenberg stayed for some months in Cambridge, England, to give lectures, and in 1950 and 1954 he was invited to lecture in the United States. In the winter of 1955-1956 he gave the Gifford Lectures at the University of St. Andrews, Scotland, these lectures being subsequently published as a book.During 1955 Heisenberg was occupied with preparations for the removal of the Max Planck Institute for Physics to Munich. Still Director of this Institute, he went with it to Munich and in 1958 he was appointed Professor of Physics in the University of Munich. His Institute was then being renamed the Max Planck Institute for Physics and Astrophysics.Heisenberg's name will always be associated with his theory of quantum mechanics, published in 1925, when he was only 23 years old. For this theory and the applications of it which resulted especially in the discovery of allotropic forms of hydrogen, Heisenberg was awarded the Nobel Prize for Physics for 1932.His new theory was based only on what can be observed, that is to say, on the radiation emitted by the atom. We cannot, he said, always assign to an electron a position in space at a given time, nor follow it in its orbit, so that we cannot assume that the planetary orbits postulated by Niels Bohr actually exist. Mechanical quantities, such as position, velocity, etc. should be represented, not by ordinary numbers, but by abstract mathematical structures called "matrices" and he formulated his new theory in terms of matrix equations.Later Heisenberg stated his famous //principle of uncertainty//, which lays it down that the determination of the position and momentum of a mobile particle necessarily contains errors the product of which cannot be less than the quantum constant //h// and that, although these errors are negligible on the human scale, they cannot be ignored in studies of the atom. Erwin Schrödinger 1887-1961 He was an Austrian scientist who loved anything to do with the atomic theory. He spent much of his time trying to improve the atomic model and received the Nobel Prize in 1933 for his work. ~ all pictures from google image search engine ~ ~all facts from either wikipedia or the nobel prize website~ =** Models ** = --Small, sphereical, solid, indivisible model --Electron fluff model --Plum Pudding model --Rutherford-Bujr model --Planetary model Electron cloud model [] The cloud model represents a sort of history of where the electron has probably been and where it is likely to be going. The red dot in the middle represents the nucleus while the red dot around the outside represents an instance of the electron. Imagine, as the electron moves it leaves a trace of where it was. This collection of traces quickly begins to resemble a cloud. The probable locations of the electron predicted by Schrödinger's equation happen to coincide with the locations specified in Bohr's model.

source http://www.regentsprep.org/regents/physics/phys05/catomodel/cloud.htm



Plum Pudding Model

The [|Plum Pudding Model] is an [|atom model] proposed by JJ Thomson, the physicist who discovered the electron. It is also known as the Chocolate Chip Cookie or Blueberry Muffin Model. You can easily picture it by imagining the said goodies. For example, you can imagine a plum pudding wherein the pudding itself is positively charged and the plums, dotting the dough, are the negatively charged electrons.

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Rutherford-Bohr model

Because the Bohr Model is a modification of the earlier Rutherford Model, some people call Bohr's Model the Rutherford-Bohr Model. The modern model of the atom is based on quantum mechanics. The Bohr Model contains some errors, but it is important because it describes most of the accepted features of atomic theory without all of the high-level math of the modern version. Unlike earlier models, the Bohr Model explains the Rydberg formula for the spectral emission lines of atomic hydrogen. The Bohr Model is a planetary model in which the negatively-charged electrons orbit a small, positively-charged nucleus similar to the planets orbiting the Sun (except that the orbits are not planar). The gravitational force of the solar system is mathematically akin to the Coulomb (electrical) force between the positively-charged nucleus and the negatively-charged electrons.

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 Atomic Planetary Model

The Bohr Model is probably familar as the "planetary model" of the atom illustrated in the adjacent figure that, for example, is used as a symbol for atomic energy (a bit of a misnomer, since the energy in "atomic energy" is actually the energy of the nucleus, rather than the entire atom). In the Bohr Model the neutrons and protons (symbolized by red and blue balls in the adjacent image) occupy a dense central region called the nucleus, and the electrons orbit the nucleus much like planets orbiting the Sun (but the orbits are not confined to a plane as is approximately true in the Solar System). The adjacent image is not to scale since in the realistic case the radius of the nucleus is about 100,000 times smaller than the radius of the entire atom, and as far as we can tell electrons are point particles without a physical extent. This similarity between a planetary model and the Bohr Model of the atom ultimately arises because the attractive gravitational force in a solar system and the attractive Coulomb (electrical) force between the positively charged nucleus and the negatively charged electrons in an atom are mathematically of the same form. (The form is the same, but the intrinsic strength of the Coulomb interaction is much larger than that of the gravitational interaction; in addition, there are positive and negative electrical charges so the Coulomb interaction can be either attractive or repulsive, but gravitation is always attractive in our present Universe.)

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