Fall.2008.MMA.Perry.Timeline

democritus


 * Born in 460 B.C in Thrace
 * Died in 370 B.C

Contribution : One of the early atomic theorists

Bio: "hypothesized that all matter is composed of tiny indestructible units, called atoms. His atomic theory was that atoms come together to create and object. therefore sharper atoms associate with sharper tools and smooth atoms associate with smoother objects. Democritus says that atoms are "indivisible" and cannot be split up into smaller components."

Leucippus




 * Born 5 B.C in Miletus, Greece
 * Died in 5 B.C

Contribution : Father of Atomism

Bio: As one of the early atomist philospophers, Leucippus was a pupil of democritus. He also came to the belief that elements were made up of indivisible matter known as an atom which is the smallest unit in the universe. Also came to say that the universe consists of two elements, The "solid" and the "void".

"Nothing happens at random, But everything from reason and necessity" -Leucippus

Antoine Lavoisier


 * Born Aug. 26, 1743 Paris, France
 * Died May 8th, 1794 Paris, France

Contibution: explaination of chemical combustion.

Bio: "Lavoisier made the discovery that water is made of hydrogen and oxygen. He also correctly figured that elements had combined chemically with air during combustion. Though he did not know at that time exactly what elements make up air. Another discovery by him was that when some of the chemicals in which he burned seemed to gain weight after they were combusted. By weighing the substance before the combustion he was able to confirm his discovery. Unfortuately Lavoisier was put to execution by the French at the mercy of the gullotine. At this time there was an unstable government in France not even providing a chance for Lavoisier to stand a trial."

Baron Berzelius


 * born in Linkoping, Sweden, 20 Aug., 1779
 * Died in 7 Aug., 1848 in stockholm, Sweden

Contribution: elements have electrically polarized atoms/ inventor of modern chemical notation

Bio: "This theory was founded on the supposition that the atoms of the elements are electrically polarized, the positive charge predominating in some and the negative in others, and from it followed his dualistic hypothesis, according to which compounds are made up of two electrically different components". -Berzelius is also credited with originating the chemical terms catalyst,polymer, and isomers. although his original definitions differed dramatically from modern usage. He coined the term "polymer" in 1833 to describe organic compounds which shared identical empirical formulas but differed in overall molecular weight, the larger of the compounds being described as "polymers" of the smallest

John Dalton


 * Born sept. 6 1766 in Cumberland, England
 * Died Manchester, England july 27, 1844

Contribution: proposed early atomic theory

Bio: "//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). Although Quite a smart man John lead a quiet simple life with no wife an little money, Sadly he died of a stroke in 1844."

Avogadro


 * Born Aug. 9, 1776 in Italy
 * Died July 9, 1856 in Italy

Contribution: Avogado's number

Bio: "Avogadro put forth the hypothesis that equal volumes of gases under the same conditions of pressure and temperature contain the same number of particles. "Later physicists and chemists determined the value of "Avogadro's Number," the number of gas molecules in one mole (the atomic or molecular weight in grams), as 6.022 x 10 23" . Avogadro's number is used to compute the results of chemical reactions. It allows chemists to determine the exact amounts of substances produced in a given reaction."

Dmitry Mendeleyev


 * Born Feb. 8 1834, in Russia
 * Died Feb. 2 1907, Russia

Contibution: Periodic table

Bio: Mendeleyev is credited to be the man who is responsible for what is now the periodic table of elements. With his table he predicted the properties of the elements which at this time were yet to be discovered.


 * 1) "The Elements, if arranged according to their atomic mass, exhibit an apparent periodicity of properties.
 * 2) Elements which are similar in regards to their chemical properties have atomic weights which are either of nearly the same value (e.g., Pt, Ir, Os) or which increase regularly (e.g., K, Rb, Cs).
 * 3) The arrangement of the elements in groups of elements in the order of their atomic weights corresponds to their so-called valencies, as well as, to some extent, to their distinctive chemical properties; as is apparent among other series in that of Li, Be, B, C, N, O, and F.
 * 4) The elements which are the most widely diffused have small atomic weights.
 * 5) The magnitude of the atomic weight determines the character of the element, just as the magnitude of the molecule determines the character of a compound body.
 * 6) We must expect the discovery of many yet unknown elements–for example, two elements, analogous to aluminum and silicon, whose atomic weights would be between 65 and 75.
 * 7) The atomic weight of an element may sometimes be amended by a knowledge of those of its contiguous elements. Thus the atomic weight of terellium must lie between 123 and 126, and cannot be 128. //Here Mendeleev was wrong as the atomic mass of tellurium (127.6) remains higher than that of iodine (126.9).//
 * 8) Certain characteristic properties of elements can be foretold from their atomic weights"

-dependence between the properties of atomic weights of the elements

Kirchhorf


 * Born in Prussia, Germany march 12, 1824
 * Died in Berlin, Germany Oct. 17, 1887

Contibution: Spectrum analysis

Bio: Alot of kirchhoff's work was dependent on the basis of spectrum analysis and the use of electrical circuits. From his work we get his 3 laws later matched up to make sense of the atoms energy with Bohr's model.

-" Kirchhoff's three laws of spectroscopy: Kirchhoff did not know about the existence of energy levels in atoms. The existence of discrete spectral lines was later explained by the Bohr model of the atom, which helped lead to quantum mechanics"
 * 1) A hot solid object produces light with a continuous spectrum.
 * 2) A hot tenuous gas produces light with spectral lines at discrete wavelengths (i.e. specific colors) which depend on the energy levels of the atoms in the gas. (//See also:// emission spectrum)
 * 3) A hot solid object surrounded by a cool tenuous gas (i.e. cooler than the hot object) produces light with an almost continuous spectrum which has gaps at discrete wavelengths depending on the energy levels of the atoms in the gas. (//See also:// absorption spectrum)

Becquerel


 * Born Dec. 18, 1852 in Paris, France
 * Died Aug. 25, 1908 in Brittany, France

Contribution: radioactivity

Bio: His mistaken discovery story : "working with crystals of a uranium compound (potassium uranyl sulfate), which, after exposure to sunlight, emitted fluorescent light. To determine whether X-rays were being emitted by the compound, he prepared a photographic plate for use after exposing a sample of the uranium salt to the Sun. As it turned out, a cloudy period ensued, during which no sunlight was available. Becquerel was at an impasse. He wrapped the crystals and a copper cross in a black cloth with the photosensitive plate and put them in a drawer, intending to retrieve them later. Quite a number of rainy days followed, with no sunlight"

"He finally removed the plate from the drawer and developed it, expecting to see some faint evidence of emission of radiation. To his immense surprise, the photographic plate revealed a distinct image of the copper cross, evidence that strong radiation must have come from the uranium compound itself. In this manner, he accidentally discovered the phenomenon that came to be known as "radioactivity" ".

It was said that he was so into his work that he knowingly would risk his own health to expieriment with radioactive substances by being burned in order to understand its effect. If thats not commitment, then what is?

Henry Cavendish


 * Born on Oct. 10, 1731 in Nice, France
 * Died in Clapham, England on Feb. 24, 1810

Contribution: discovery of hydrogen

Bio: "Cavendish is generally credited with having discovered, hydrogen since he had described the density of "inflammable air," which formed water on combustion". "He Also discovered that when hydrogen and oxygen are enclosed in a tube, and the reaction between them triggered by a spark, water vapor condenses on the sides of the tube. He calculated the weights of each gas, and showed that it was equal to the weight of the water formed." Another amazing feature of this man was that he established an accurate measure of the earth's Atmospere.

J.J Thomson


 * Born Dec. 18, 1856 in Cheetham Hill, England
 * Died on Aug. 30 1940 in Cambridge, England

Contribution: discovery of the electron

Bio: "Dalton made fundamental contributions to the scientific understanding of gases. He first stated the law of partial pressures. This law e plains that the total pressure in a mixture of gases equals the sum of the pressure exerted independently by each gas. It is now called Dalton's law." "The atomic theory proposes that all matter is made up of very tiny particles called atoms. Dalton refined the theory by suggesting that each chemical element consists of a Single type of atom. Although an amount of the element may contain many, many atoms, they are all identical in size, shape, and mass."

Plum Pudding model

> ball of positive material of pudding-like > consistency in which were embedded > discrete negatively charged objects > called electrons
 * The atom was once thought to be a solid

Erwin Schroedinger


 * born on August 12, 1887, in Vienna
 * He died on the 4th of January, 1961

Contribution: wave equation and electon cloud model

Bio: "Erwin Schrodinger was one of the main architects of quantum mechanics. Schrodinger developed the wave mechanics. It became the second formulation of quantum mechanics". ''the solutions to Schrodinger’s wave equation are wave functions that can only be related to probable occurrence of physical events. Schrodinger’s wave equation is a mathematically sound atomic theory. It is regarded by many as the single most important contribution to theoretical physics in the twentieth century."

Electron cloud model- "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.

a short ans sweet definition: -An electron cloud is a visual model of the most probable locations of electrons in an atom. The cloud is denser where you will probably find an electron. The electron cloud model is used to describe the possible locations of electrons around the nucleus."

Marie Curie


 * born in Warsaw on November 7, 1867
 * died in Savoy, France, after a short illness, on July 4, 1934

Contribution: nuclear chemist

Bio: "Curie is a scientific icon remembered for her pioneering work in the field of radiation research. She discovered Radium and Polonium, defining their atomic weight and their place in the periodic system, and she was the first to discover methods for extracting pure Radium salts and metal. She who first coined the term "radioactivity", was key in developing methods for quantitatively measuring radioactivity and for discovering its effect on living cells." "awarded the Nobel Prize, first in 1903 in Physics and then again in 1911 in the field of Chemistry. She was the first person ever to be awarded two Noble Prizes." " Working in the lab she shared with Pierre, she soon discovered that the level of radiation emitted depended only on the quantity of the Uranium contained in a compound, and not on the types of other elements that the compound contained. This meant that the "radioactivity", as she dubbed it, was not the result of a reaction //between// elements, but was instead the result of something going on //within// the Uranium atoms themselves." - nndb.com

Pierre Currie


 * Born on may 15, 1859 in France
 * Died April 19, 1906 in France

Contribution: investigator of radiation

Bio: "Curie's studies of radioactive substances were made together with his wife, whom he married in 1895 Marie. They announced the discovery of radium and polonium by fractionation of pitchblende in 1898." Worked hand in hand with Marie Curie.

- born in Copenhagen on October 7, 1885 -died on 18 of nov.1962, in denmark
 * Niels bohr** [[image:http://nobelprize.org/nobel_prizes/physics/laureates/1922/bohr.jpg width="136" height="216" caption="Niels Bohr"]]

Contribution: father of quantum theory

Bio: "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." Bohr also was a major part of the manhattan project, this was the American nuclear bomb. Neils was in favor of sharing the information with the Russians and scientific community in hopes of speeding the process, however was rejected.

-the Bohr model depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus—similar in structure to the solar system, but with electrostatic forces providing attraction, rather than gravity.

Theodore William Richards


 * was born in Germantown, Pennsylvania, USA on January 31, 1868
 * died at Cambridge, Massachusetts, on April 2, 1928

Contribution: existance of isotopes

BIO: "Richards was the first to show, by chemical analysis, that an element could have different atomic weights. He was asked to analyze samples of naturally-occurring lead and lead produced by radioactive decay. His measurements showed that the two samples had different atomic weights, supporting the concepts of isotopes." "Other scientific work of Theodore Richards included investigations of the compressibilities of atoms, heats of solution and neutralization, and the electrochemistry of amalgams. His investigation of electrochemical potentials at low temperatures was among the work that led, in the hands of others, to the Nernst heat theorem and the third law of thermodynamics".

Ernest Rutherford


 * born on August 30, 1871, in Nelson, New Zealand
 * Cambridge on October 19, 1937

Contributions: father of nuclear phyics

Bio: "Rutherford discovered the atomic nucleus and developed a model of the atom that was similar to the solar system.Rutherford was also the first to establish the theory of the nuclear atom and to carry out a transmutation reaction.He then discovered the half-life of radioactive elements and applied this to studies of age determination of rocks by measuring the decay period of radium to lead-206." Responsible for the Planetary Model below:

Planetary model

-"created a planetary model of atom exploring a dispersion of a  -particles transiting through a thin metal foil. According to this model an atom looks like a tiny planetary system, in which the forces of an electrical attraction operate. The center of an atom is a positively charged kern. Almost all mass of an atom is focused there. Negatively charged eletrons rotate around the kern."

Chadwick


 * Born 1891 Oct. 20 in Manchester, England
 * Died on July 24, 1974 in Cambridge, England

Contribution: discovered the neutron

Bio: "In 1932 he discovered the fourth known subatomic particle, the neutron (following the electron, photon, and proton); its existence had been suspected since 1924. Chadwick's later experiments with particle accelerators contributed to the invention of the nuclear bomb." -Answers.com -His dicovery made it possible for scientist to make a new element heavier then that of Uranium. For his discoveries he is awarded the Noble prize in 1935.

Woks cited: 1. [|http://library.thinkquest.org] 2. http://www.vigyanprasar.gov.in/scientists 3. [|http://scienceworld.wolfram.com] 4. http://sol.sci.uop.edu/ 5. http://www.epa.gov/rpdweb00/understand/rutherford.html 6. wikipedia.com 7. http://library.thinkquest.org/C006439/scientists 8. http://www.nndb.com/people 9. [|http://nobelprize.org] 10. [|http://www.answers.com]