:: wikimiki.org ::
| Odd Molecule |
Odd moleculeOdd molecule is a term invented by Gilbert N. Lewis in 1916 for a molecule containing an odd number of electrons.
Taking the p-shell elements, such molecules are rare; they are usually colored and paramagnetic, that is, attracted by a magnet.
Odd molecules are 'radicals'; see radicals.
A fine example is nitric oxide, q.v.; nitrogen dioxide is another; chlorine dioxide is also an example, being a reddish-yellow gas. They are all fairly reactive.
When including d-shell elements, i.e., the transition metals, the concept mostly doesn't apply, and this 'odd' state is not so unusual.
References
- "The Atom and the Molecule", Gilbert N. Lewis, Journal of the American Chemical Society, volume 38 (1916), pages 762–786; received January 26, 1916.
- [http://dbhs.wvusd.k12.ca.us/webdocs/Chem-History/Lewis-1916/Lewis-1916.html "Classic Papers" - online copy of 1916 paper - 2005-V-17]
Category:Molecular physics
Gilbert N. Lewis
Gilbert Newton Lewis (October 23, 1875-March 23, 1946) was a famous American physical chemist.
Early life
Lewis was born in Weymouth, Massachusetts as the son of a Dartmouth-graduated lawyer/broker. He was a precocious child who learned to read at age three.
His family moved to Lincoln, Nebraska when he was 9. He was homeschooled until age 9. He went to public school from age 9 to 14 and then he went to the University of Nebraska, and three years later transferred to the Harvard University where he showed an interest in economics, but concentrated in chemistry, getting his B.A. in 1896 and his Ph.D. in 1899. His first published work, a study of thermochemical and electrochemical properties of amalgams, was based on his doctoral research and was published in 1898.
Career
After earning his Ph.D., he stayed as an instructor for a year before taking a traveling fellowship, studying under the physical chemist Wilhelm Ostwald at Leipzig and Walther Nernst at Göttingen. He then returned to Harvard as an instructor for three more years, and in 1904 left to become superintendent of weights and measures for the Bureau of Science of the Philippine Islands in Manila. The next year he returned to Cambridge when the Massachusetts Institute of Technology (MIT) appointed him to a faculty position, in which he had a chance to join a group of outstanding physical chemists under the direction of Arthur Amos Noyes. He quickly rose in rank, becoming assistant professor in 1907, associate professor on 1908, and full professor in 1911. He left MIT to become professor of physical chemistry and dean of the College of Chemistry at the University of California, Berkeley in 1912. Lewis Hall at Berkeley, built in 1948, was named in his honor.
In 1908 he published the first of several papers on relativity, in which he derived the mass-energy relationship in a different way from Albert Einstein's derivation. He also introduced the thermodynamic concept of fugacity in a paper, "The osmotic pressure of concentrated solutions, and the laws of the perfect solution," J. Am. Chem. Soc. 30, 668-683 (1908).
On June 21, 1912, he married Mary Hinckley Sheldon, daughter of a Harvard professor of Romance languages. They had two sons, both of whom became chemistry professors, and a daughter.
In 1913, he was elected to the National Academy of Sciences, but in 1934 he resigned in a dispute over the internal politics of that institution.
In 1916, he formulated the idea that a covalent bond consisted of a shared pair of electrons and defined the term odd molecule when an electron is not shared. His ideas on chemical bonding were expanded upon by Irving Langmuir and became the inspiration for the studies on the nature of the chemical bond by Linus Pauling.
In 1919, by studying the magnetic properties of solutions of oxygen in liquid nitrogen, he found that O4 molecules were formed. This was the first evidence for tetratomic oxygen.
In 1923, he formulated the electron-pair theory of acid-base reactions. In the so-called Lewis theory of acids and bases, a "Lewis acid" is an electron-pair acceptor and a "Lewis base" is an electron-pair donor.
Students of chemistry learn about a notation system for the valence electrons which is known as the Lewis dot structure.
Based on work by J. Willard Gibbs, it was known that chemical reactions proceeded to an equilibrium determined by the free energy of the substances taking part. Lewis spent 25 years determining free energies of various substances. In 1923 he and Merle Randall published the results of this study and formalizing chemical thermodynamics.
In 1926, he coined the term "photon" for the smallest unit of radiant energy.
Lewis was the first to produce a pure sample of deuterium oxide (heavy water) in 1933. By accelerating deuterons (deuterium nuclei) in Ernest O. Lawrence's cyclotron, he was able to study many of the properties of atomic nuclei.
In the last years of his life, he established that phosphorescence of organic molecules involves an excited triplet state (a state in which electrons that would normally be paired with opposite spins are instead excited to have their spin vectors in the same direction) and measured the magnetic properties of this triplet state.
During his career he published on many other subjects besides those mentioned in this article, ranging from the nature of light quanta to the economics of price stabilization.
He died at age 70 of a heart attack while working in his laboratory in Berkeley.
Lewis, Gilbert Newton
Lewis, Gilbert Newton
Lewis, G. N.
Lewis, G. N.
ja:ギルバート・ルイス
1916
1916 (MCMXVI) is a leap year starting on Saturday (link will take you to calendar)
Events
January-February
- January 1 -The first successful blood transfusion using blood that had been stored and cooled. Impressionist Monet paints 'Water Lilies'.
- January 5 - Heavy rain - allegedly caused by rainmaker Charles Hatfield - begins; it will cause flooding around San Diego, California
- January 8 - Allied forces withdraw from Gallipoli
- January 13/14 - A heavy storm sweeps through the Zuiderzee in the Netherlands, causing extensive damage. This storm helped the Dutch parliament to decide to build the Afsluitdijk and build polders in the current IJsselmeer.
- January 17 - The Professional Golfers Association (PGA) is formed
- January 18 - A 611 gram chondrite type meteorite struck a house near Baxter, Stone County, Missouri.
- January 23 to 24 In Browning, Montana, the temperature drops from +6.7°C to -48.8°C (44°F to -56°F) in one day, the greatest change ever on record for a 24-hour period.
- January 24 - In Brushaber v. Union Pacific Railroad the Supreme Court of the United States declares the federal income tax void
- January 28 - Louis D. Brandeis becomes the first Jew appointed to the Supreme Court of the United States.
- January 29 - World War I: Paris is bombed by German zeppelins for the first time.
- February 2 - Blizzard in Victoria, British Columbia, Canada
- February 3 - Parliament buildings in Ottawa, Canada are burned down.
- February 9 - 6.00 PM - Tristan Tzara "founds" Dadaism (according to Hans Arp
- February 11 - Emma Goldman is arrested for lecturing on birth control.
- February 11 - Baltimore Symphony Orchestra presents its first concert
- February 21 - World War I: In France the Battle of Verdun begins.
March-June
- March 1 - Liberal British Columbia Premier Harlan Carey Brewster term in office ends
- March 6 - Sydney conservatorium of music in Australia accepts first students
- March 8-9 night - Mexican Revolution - Pancho Villa leads 1,500 Mexican raiders in an attack against Columbus, New Mexico, killing 17. Garrison of US 13th Cavalry Regiment fights back and drives them away.
- March 15 - President Woodrow Wilson sends 12,000 United States troops over the U.S.-Mexico border border to pursue Pancho Villa; 13th Cavalry regiment enters Mexican territory.
- March 16 - US 7th and 10th cavalry regiments under John J. Pershing crosses the border to join the hunt of Villa
- March 19 - First United States air combat mission in history as eight US planes take off in pursuit of Pancho Villa
- March 22 - Marriage of Edith Bratt and John Ronald Reuel Tolkien. They would serve as the inspiration for the fictional characters Lúthien and Beren.
- April 24 - April 30 - Easter Rising in Ireland
- April 27 - Battle of Hulluch in World War One, 47th Brigade, 16th Irish Division decimated in one of the most heavily-concentrated gas attacks of the war
- May 5 - United States Marines invade the Dominican Republic.
- May 20 - The Saturday Evening Post publishes its first cover with a Norman Rockwell painting ("Boy with Baby Carriage").
- May 21 - Sir Ernest Shackleton and two of his companions reach a whaling station to get help for the rest of the crew of Endurance.
- May 21 - Britain initiates daylight saving time.
- May 31 - June 1 - Battle of Jutland
- June 5 - Louis Brandeis is sworn in as a Justice of the United States Supreme Court.
- June 5 - HMS Hampshire sinks off the Orkneys, Scotland, with Lord Kitchener aboard
- June 15 - U.S. President Woodrow Wilson signs a bill incorporating the Boy Scouts of America. [http://www.scouting.org/factsheets/02-507.html]
July-August
- July 1 - November 18: More than 1 million soldiers die during The Battle of the Somme including 60,000 soldiers from the British Commonwealth on the first day. The United States is still unwilling to join in the war with Britain, Canada, Australia and the other commonwealth countries.
- July 1 through July 12, at least one shark mauled five swimmers along 80 miles of New Jersey coastline during the Jersey Shore Shark Attacks of 1916, resulting in four deaths and survival of one youth who required limb amputation. This event was the inspiration for author Peter Benchley, over half a century later, to write Jaws.
- July 15 - In Seattle, Washington, William Boeing incorporates Pacific Aero Products (later renamed Boeing).
- July 16 - Hellenic Holocaust: The entire Greek population of Sinope and the coastal region of the county of Kastanome is either exiled or killed.
- July 22 - In San Francisco, California, a bomb explodes on Market Street during a Preparedness Day parade killing 10 injuring 40. (Warren Billings and Tom Mooney are later wrongly convicted of it)
- July 29 - In Ontario, Canada, a lightning strike ignites a forest fire that destroys the towns of Cochrane and Matheson - 233 dead
- 2 August - World War I: Austrian sabotage causes the sinking of Italian battleship Leonardo da Vinci in Taranto.
October-December
Taranto.]]
- October 27 - Battle of Segale: Negus Mikael, marching on the Ethiopian capital in support of his son Emperor Iyasu, is defeated by Fitawrari Habte Giyorgis, securing the throne for Empress Zauditu.
- November 5 - Kingdom of Poland proclaimed by joined act of emperors of Germany and Austria
- November 7 - Woodrow Wilson defeats Charles E. Hughes in the U.S. presidential election.
- November 7 - Republican Jeannette Rankin of Montana becomes the first woman elected to the United States House of Representatives.
- November 13 - Prime Minister of Australia William Morris Hughes is expelled from the Labor Party over his support for conscription.
- November 18 - World War I: First Battle of the Somme ends - In France, British Expeditionary Force commander Douglas Haig calls off the battle which started on July 1, 1916.
- November 25 - Friedrich Adler shoots Karl Stürgh, prime minister of Austria
- November 30 - Hellenic Holocaust: According to the Austrian consul: "on 26 November Rafet Bey (Turkish Minister of the Interior) told me: "we must finish off the Greeks as we did with the Armenians … on 28 November.""
- December 12 - In the Dolomites, an avalanche buries 18,000 Austrian and Italian soldiers.
- December 30 - Humberto Gómez and his mercenaries seize Arauca in Colombia and declare Republic of Arauca. He proceeds to pillage the region before fleeing to Venezuela
- December 23 - World War I: Battle of Magdhaba - In the Sinai desert, Australian and New Zealand mounted troops capture the Turkish garrison.
- December 31 - The Hampton Terrace Hotel in North Augusta, South Carolina, one of the largest and most luxurious hotels in the nation at the time, burns to the ground.
Unknown dates
- Hipolito Irigoyen elected as the President of Argentina.
- Blaise Diagre, first black representative of Senegal in the French parliament
- Cours de linguistique générale by Ferdinand de Saussure is published.
- Summer Olympic Games in Berlin, Germany, are cancelled.
- Food is rationed in Germany.
- Ernst Rudin published his initial results on the genetics of schizophrenia.
- The Netherlands is hit by a North Sea storm that floods lowlands and kills 10.000 people.
- Woman's International Bowling Congress established in the US.
- Robert Baden-Powell founds Wolf Scouts in Britain, changed to Cub Scouts in the USA.
- Sopwith Camel aircraft is introduced to combat the German-built Fokker fighter aircraft.
- Louis Enricht claims he has a substitute for gasoline
- Gustav Holst composes The Planets, Opus 32
- Bray Studios created the Farmer Alfalfa series, the first of theTerrytoons.
Ongoing events
- World War I (1914-1918)
- Armenian Genocide (1915-1918)
- Mexican Revolution
Births
January-March
- January 3 - Betty Furness, American actress and consumer activist (d. 1994)
- January 7 - Paul Keres, Estonian chess player
- January 9 - Peter Twinn, English mathematician and World War II code-breaker (d. 2004)
- January 10 - Sune Bergström, Swedish biochemist, recipient of the Nobel Prize in Physiology or Medicine (d. 2004)
- January 12 - Pieter Willem Botha, President of South Africa
- January 22 - Henri Dutilleux, French composer
- February 9 - Tex Hughson, baseball player (d. 1993)
- February 11 - Joseph Alioto, Mayor of San Francisco (d. 1998)
- February 14 - Masaki Kobayashi, Japanese film director
- February 26 - Jackie Gleason, American comedian (d. 1987)
- February 29 - Dinah Shore, American singer (d. 1994)
- March 3 - Paul Halmos, Hungarian-born mathematician
- March 4 - Hans Eysenck, German-born psychologist (d. 1997)
- March 11 - Harold Wilson, Prime Minister of the United Kingdom (d. 1995)
- March 13 - John Aspinwall Roosevelt, American businessman and philanthropist (d. 1981)
- March 14 - Horton Foote, American writer
- March 15 - Harry James, American musician and band leader (d. 1983)
- March 17 - Ray Ellington, British singer (d. 1985)
- March 19 - Irving Wallace, American novelist (d. 1990)
- March 26 - Christian B. Anfinsen, American chemist, Christian B. Anfinsen laureate (d. 1995)
- March 29 - Eugene McCarthy, U.S. Senator from Minnesota (d. 2005)
April-June
- April 3 - Herb Caen, American journalist (d. 1997)
- April 5 - Gregory Peck, American actor (d. 2003)
- April 11 - Alberto Ginastera, Argentine composer (d. 1983)
- April 12 - Beverly Cleary, American author
- April 15 - Alfred S. Bloomingdale, American department store heir (d. 1982)
- April 22 - Yehudi Menuhin, American-born violinist (d. 1999)
- April 25 - R.J. Rushdoony, American founder of Christian Reconstructionism (d. 2001)
- April 28 - Ferruccio Lamborghini, Italian automobile manufacturer (d. 1993)
- April 30 - Claude Elwood Shannon, American information theorist (d. 2001)
- April 30 - Robert Shaw, American conductor (d. 1999)
- May 8 - João Havelange, Brazilian industrialist and football league president
- May 10 - Milton Babbitt, American composer
- May 11 - Camilo José Cela, Spanish writer, Nobel Prize laureate (d. 2002)
- May 20 - Trebisonda Valla, Italian athlete
- May 21 - Tinus Osendarp, Dutch runner (d. 2002)
- May 21 - Harold Robbins, American novelist (d. 1997)
- May 26 - Henriette Roosenburg, Dutch journalist (d. 1972)
- June 4 - Robert F. Furchgott, American chemist, recipient of the Nobel Prize in Physiology or Medicine
- June 8 - Francis Crick, English molecular biologist, recipient of the Nobel Prize in Physiology or Medicine (d. 2004)
- June 15 - Herbert Simon, American economist, Nobel Prize laureate (d. 2001)
- June 18 - Julio César Turbay Ayala, Colombian politician (d. 2005)
- June 23 - Hermann Gmeiner, Austrian educator (d. 1986)
- June 23 - Len Hutton, English cricketer (d. 1990)
July-December
- July 2 - Hans-Ulrich Rudel, German pilot (d. 1982)
- July 9 - Sir Edward Heath, Prime Minister of the United Kingdom (d. 2005)
- July 11 - Aleksandr Mikhailovich Prokhorov, Russian physicist, Nobel laureate (d. 2002)
- July 11 - Gough Whitlam, twenty-first Prime Minister of Australia
- July 14 - Natalia Ginzburg, Italian author (d. 1991)
- July 18 - L. Patrick Gray III, director of the American Federal Bureau of Investigation (d. 2005)
- July 22 - Marcel Cerdan, French boxer (d. 1949)
- July 31 - Bill Todman, American game show producer (d. 1979)
- August 25 - Frederick Chapman Robbins, American pediatrician and virologist, recipient of the Nobel Prize in Physiology or Medicine (d. 2003)
- August 27 - Martha Raye, American actress (d. 1994)
- September 13 - Roald Dahl, Welsh author (d. 1990)
- October 3 - James Herriot, veterinarian and author (d. 1995)
- October 4 - Vitaly Ginzburg, Russian physicist, Nobel laureate
- October 19 - Jean Dausset, French immunologist, recipient of the Nobel Prize in Physiology or Medicine
- October 19 - Emil Gilels, Ukrainian pianist (d. 1994)
- October 26 - François Mitterrand, President of France (d. 1996)
- October 30 - Leon Day, baseball player (d. 1995)
- November 1 - John C. Harkness, American architect
- November 4 - Walter Cronkite, American television journalist
- November 5 - Jim Tabor, baseball player
- November 10 - Louis le Brocquy, Irish painter
- November 16 - Daws Butler, American voice actor
- November 24 - Forrest J. Ackerman, American writer
- November 27 - Chick Hearn, American basketball announcer (d. 2002)
- November 28 - Mary Lilian Baels, queen of Léopold III of the Belgians (d. 2002)
- November 29 - Fran Ryan, American actress (d. 2000)
- December 9 - Kirk Douglas, American actor
- December 11 - Dámaso Pérez Prado, Cuban musician (d. 1989)
- December 15 - Maurice Wilkins, New Zealand-born physicist, recipient of the Nobel Prize in Physiology or Medicine (d. 2004)
- December 19 - Elisabeth Noelle-Neumann, German political scientist
- Jack Agazarian, English World War II spy (d. 1945)
Deaths
- February 6 - Rubén Darío, Nicaraguan writer (b. 1867)
- February 12 - Richard Dedekind, German mathematician (b. 1831)
- February 19 - Ernst Mach, Austrian physicist and philosopher (b. 1838)
- February 20 - Klas Pontus Arnoldson, Swedish writer and pacifist, recipient of the Nobel Peace Prize (b. 1844)
- February 28 - Henry James, American writer (b. 1843)
- March 4 - Franz Marc, German artist (b. 1880)
- March 24 - Enrique Granados, Spanish composer (ship sinking) (b. 1867)
- April 19 - Ephraim Shay, American inventor (b. 1839)
- May 3 - Padraig Pearse, Irish nationalist (b. 1879)
- May 11 - Max Reger, German composer (b. 1873)
- May 13 - Sholom Aleichem, Ukrainian Yiddish writer (b. 1859)
- June 6 - Yuan Shikai, Chinese military official and politician (b. 1859)
- June 29 - Georges Lacombe, French artist (b. 1868)
- July 6 - Odilon Redon, French painter (b. 1840)
- July 16 - Ilya Ilyich Mechnikov, Russian microbiologist, recipient of the Nobel Prize in Physiology or Medicine (b. 1845)
- July 23 - Sir William Ramsay, Scottish chemist, Nobel Prize laureate (b. 1852)
- August 31 - Martha McClellan Brown, American temperance movement leader (b. 1838)
- September 4 - José Echegaray y Eizaguirre, Spanish writer, Nobel Prize laureate (b. 1832)
- October 7 - James Whitcomb Riley, American poet (b. 1849)
- October 28 - Cleveland Abbe, American meteorologist (b. 1838)
- November 13 - Lanoe Hawker, British fighter pilot (b. 1890)
- November 14 - Saki, British writer (b. 1870)
- November 15 - Henryk Sienkiewicz, Polish writer, Nobel Prize laureate (b. 1846)
- November 21 - Emperor Franz Joseph I of Austria (b. 1830)
- November 22 - Jack London, American author (b. 1876)
- November 24 - Hiram Stevens Maxim, American firearms inventor (b. 1840)
- December 28 - Eduard Strauss, Austrian composer (b. 1835)
- December 29 - Grigori Rasputin, Russian mystic (b. 1870)
Nobel Prizes
- Physics - not awarded
- Chemistry - not awarded
- Medicine - not awarded
- Literature - Carl Gustaf Verner von Heidenstam
- Peace - not awarded
Category:1916
ko:1916년
ja:1916年
simple:1916
th:พ.ศ. 2459
MoleculeA molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. The science of molecules is called molecular chemistry or molecular physics, depending on the focus. Molecular chemistry deals with the laws governing the interaction between molecules that results in the formation and breakage of chemical bonds, while molecular physics deals with the laws governing their structure and properties. In practice, however, this distinction is vague.
According to the strict definition, molecules can consist of one atom (as in noble gases) or more atoms bonded together. The concept of monatomic (single-atom) molecule is used almost exclusively in the kinetic theory of gases. In molecular sciences, a molecule consists of a stable system (bound state) comprising two or more atoms. The term unstable molecule is used for very reactive species, i.e., short-lived assemblies (resonances) of electrons and nuclei, such as radicals, molecular ions, Rydberg molecules, transition states, Van der Waals complexes, or systems of colliding atoms as in Bose-Einstein condensates. A peculiar use of the term molecular is as a synonym to covalent, which arises from the fact that, unlike molecular covalent compounds, ionic compounds do not yield well-defined smallest particles that would be consistent with the definition above. No typical "smallest particle" can be defined for covalent crystals, or network solids, which are composed of repeating unit cells that extend indefinitely either in a plane (such as in graphite) or three-dimensionally (such as in diamond).
Although the concept of molecules was first introduced in 1811 by Avogadro, and was accepted by many chemists as a result of Dalton's laws of Definite and Multiple Proportions (1803-1808), with notable exceptions (Boltzmann, Maxwell, Gibbs), the existence of molecules as anything other than convenient mathematical constructs was still an open debate in the physics community until the work of Perrin (1911), and was strenuously resisted by early positvists such as Mach. The modern theory of molecules makes great use of the many numerical techniques offered by computational chemistry. Dozens of molecules have now been identified in interstellar space by microwave spectroscopy.
microwave spectroscopy (right) representations of the terpenoid, atisane. In the 3D model on the left, carbon atoms are represented by gray spheres; white spheres represent the hydrogen atoms and the cylinders represent the bonds. The model is enveloped in a "mesh" representation of the molecular surface, colored by areas of positive (red) and negative (blue) electric charge. In the 3D model (center), the light-blue spheres represent carbon atoms, the white spheres are hydrogen atoms, and the cylinders in between the atoms correspond to single bonds.]]
Chemical bond
:See main article chemical bond
In a molecule, the atoms are joined by shared pairs of electrons in a chemical bond. It may consist of atoms of the same chemical element, as with oxygen (O2), or of different elements, as with water (H2O).
Size
Most molecules are much too small to be seen with the naked eye, but there are exceptions. DNA, a macromolecule, can reach macroscopic sizes.
The smallest molecule is the hydrogen molecule. The interatomic distance is 0.15 nanometres (1.5 Å). But the size of its electron cloud is difficult to define precisely. Under standard conditions molecules have a dimension of a few to a few dozen Å.
Empirical formula
:See main article empirical formula
The empirical formula of a molecule is the simplest integer ratio of the chemical elements that constitute the compound. For example, in their pure forms, water is always composed of a 2:1 ratio of hydrogen to oxygen, and ethyl alcohol or ethanol is always composed of carbon, hydrogen, and oxygen in a 2:6:1 ratio. However, this does not determine the kind of molecule uniquely - dimethyl ether has the same ratio as ethanol, for instance. Molecules with the same atoms in different arrangements are called isomers. The empirical formula is often the same as the molecular formula but not always. For example the molecule acetylene has molecular formula C2H2, but the simplest integer ratio of elements is CH.
Chemical formula
:See main article chemical formula
The chemical formula reflects the exact number of atoms that compose a molecule. The molecular mass can be calculated from the chemical formula and is expressed in conventional units equal to 1/12 from the mass of a 12C isotope atom. For network solids, the term formula unit is used in stoichiometric calculations.
Molecular geometry
:See main article molecular geometry
Molecules have fixed equilibrium geometries—bond lengths and angles—. A pure substance is composed of molecules with the same geometrical structure. The chemical formula and the structure of a molecule are the two important factors that determine its properties, particularly its reactivity. Isomers share a chemical formula but normally have very different properties because of their different structures. Stereoisomers, a particular type of isomers, may have very similar physico-chemical properties and at the same time very different biochemical activities.
Molecular spectroscopy
:See main article spectroscopy
Molecular spectroscopy is the study of the response (spectrum) of a molecule to a signal of known energy (or frequency, according to Planck's formula). This signal is usually an electromagnetic wave or a beam of electrons, but new molecular spectroscopies, such as the positron spectroscopy, are under development. The molecular response can be signal absorption (absorption spectroscopy), emission of another signal (emission spectroscopy), fragmentation, or a change in its chemical nature.
Spectroscopy is recognized as the most powerful tool in the investigation of the microscopic properties of molecules, and, in particular, their energy levels. Nowadays, in order to extract the maximum microscopic information from the experimental results, spectroscopical studies are very often coupled with computational chemical investigations. The theoretical background of spectroscopy is the scattering theory.
See also
- Covalent bond
- Diatomic molecule
- Molecular geometry
- Molecular orbital
- Nonpolar molecule
- Polar molecule
Related lists
- For a list of molecules see the List of compounds
- List of molecules in interstellar space
Category:Matter
als:Molekül
ko:분자
ja:分子
simple:Molecule
th:โมเลกุล
Electron
The electron is a fundamental subatomic particle which carries a negative electric charge.
Overview
Within an atom the electrons surround the nucleus of protons and neutrons in an electron configuration. The word electron was coined in 1894 and is derived from the term electric, whose ultimate origin is the Greek word 'ηλεκτρον, meaning amber.
Electrons in motion constitute electric current which may be used by scientists and engineers to measure many physical properties. Electric current existing for a finite time gives rise to a movement of charge (electricity) that may be harnessed as a practical means to perform work.
The variations in electric field generated by differing numbers of electrons and their configurations in atoms determine the chemical properties of the elements. These fields play a fundamental role in chemical bonds and chemistry.
Electrons in practice
Classification of electrons
The electron is one of a class of subatomic particles called leptons which are believed to be fundamental particles (that is, they cannot be broken down into smaller constituent parts). The word "particle" is somewhat misleading however, because quantum mechanics shows that electrons also behave like a wave, e.g. in the double-slit experiment; this is called wave-particle duality.
The antiparticle of an electron is the positron, which has the same mass but positive rather than negative charge. The term negatron is sometimes used to refer to standard electrons so that the term electron may be used to describe both positrons and negatrons, as proposed by Carl D. Anderson. Under ordinary circumstances, however, electron refers to the negatively charged particle alone.
Properties and behavior of electrons
Electrons have a negative electric charge of −1.6 × 10−19 coulombs, and a mass of about 9.11 × 10−31 kg (0.51 MeV/c2), which is approximately 1⁄1836 of the mass of the proton. These are commonly represented as e−.
According to quantum mechanics, electrons can be represented by wavefunctions, from which the electron density can be determined. The exact momentum and position of an electron cannot be simultaneously determined. This is a limitation described by the Heisenberg uncertainty principle, which, in this instance, simply states that the more accurately we know a particle's position, the less accurately we can know its momentum and vice versa.
The electron has spin ½, which implies it is a fermion, i.e., it follows the Fermi-Dirac statistics. While most electrons are found in atoms, others move independently in matter, or together as an electron beam in a vacuum. In some superconductors, electrons move in Cooper pairs, in which their motion is coupled to nearby matter via lattice vibrations called phonons. When electrons move, free of the nuclei of atoms, and there is a net flow, this flow is called electricity, or an electric current.
A body has a static charge when the body has more or fewer electrons than are required to balance the positive charge of the nuclei. When there is an excess of electrons, the object is said to be negatively charged. When there are fewer electrons than protons, the object is said to be positively charged. When the number of electrons and the number of protons are equal, their charges cancel out and the object is said to be electrically neutral. A macroscopic body can acquire charge through rubbing, i.e. the phenomena of triboelectricity. Electrons and positrons can annihilate each other and produce a pair of photons. Conversely, high-energy photons may transform into an electron and a positron by a process called pair production.
The electron is an elementary particle — that means that it has no substructure (at least, experiments have not found any so far, and there is good reason to believe that there is not any). Hence, it is usually described as point-like, i.e. with no spatial extension. However, if one gets very near an electron, one notices that its properties (charge and mass) seem to change. This is an effect common to all elementary particles: the particle influences the vacuum fluctuations in its vicinity, so that the properties one observes from far away are the sum of the bare properties and the vacuum effects (see renormalization).
There is a physical constant called the classical electron radius, with a value of 2.8179 × 10−15 m. Note that this is the radius that one could infer from its charge if the physics were only described by the classical theory of electrodynamics and there were no quantum mechanics (hence, it is an outdated concept that nevertheless sometimes still proves useful in calculations).
The speed of an electron in a vacuum can approach, but never reach c, the speed of light in a vacuum. This is due to an effect of special relativity. The effects of special relativity are based on a quantity known as gamma or the Lorentz factor. Gamma is a function of v, the velocity of the particle, and c. The following is the formula for gamma:
:
The energy necessary to accelerate a particle is gamma minus one times the rest mass. For example, the linear accelerator at Stanford can [http://www2.slac.stanford.edu/vvc/theory/relativity.html accelerate] an electron to roughly 51 GeV. This gives you a gamma of 100,000 given that the rest mass of an electron is 0.51 MeV/c² (the relativistic mass of this fast electron is 100 000 times its rest mass). Solving the equation above for the speed of the electron gives a speed of:
: = 0.999 999 999 95 c.
(The formula applies for large γ.)
Electrons in the universe
It is believed that the number of electrons existing in the known universe is at least 1079. This number amounts to a density of about one electron per cubic metre of space.
Based on the classical electron radius and assuming a dense sphere packing, it can be calculated that the number of electrons that would fit in the observable universe is on the order of 10130. Of course, this number is even less meaningful than the classical electron radius itself.
Electrons in industry
Electron beams are used in welding as well as lithography.
Electrons in the laboratory
Early experiments
The quantum or discrete nature of electron's charge was observed by Robert Millikan in the Oil-drop experiment of 1909.
Use of electrons in the laboratory
Electron microscopes are used to magnify details up to 500,000 times. Quantum effects of electrons are used in Scanning tunneling microscope to study features at the atomic scale.
Electrons in theory
In relativistic quantum mechanics, the electron is described by the Dirac Equation. Quantum electrodynamics (QED) models an electron as a charged particle surrounded a sea of interacting virtual particles, modifying the sea of virtual particles which makes up a vacuum. Although this theory involves difficult theoretical problems where calculations produce infinite terms, a practical (although mathematically dubious) method called renormalization was discovered whereby infinite terms can be cancelled to produce finite predictions about the electron. The correction of just over 0.1% to the predicted value of the electron's gyromagnetic ratio from exactly 2 (as predicted by Dirac's single particle model), and its extraordinarily precise agreement with the experimentally determined value, is viewed as one of the pinnacles of modern physics. There are now indications that string theory and its descendants may provide a model of the electron and other fundamental particles where the infinities in calculations do not appear, because the electron is no longer seen as a dimensionless point. At present, string theory is very much a 'work in progress' and lacks predictions analogous to those made by QED that can be experimentally verified.
In the Standard Model of particle physics, it forms a doublet in SU(2) with the electron neutrino, as they interact through the weak interaction. The electron has two more massive partners, with the same charge but different masses: the muon and the tau lepton.
The antimatter counterpart of the electron is its antiparticle, the positron. The positron has the same amount of electrical charge as the electron, except that the charge is positive. It has the same mass and spin as the electron. When an electron and a positron meet, they may annihilate each other, giving rise to two gamma-ray photons, each having an energy of 0.511 MeV (511 keV). See also Electron-positron annihilation.
Electrons are also a key element in electromagnetism, an approximate theory that is adequate for macroscopic systems, and for classical modelling of microscopic systems.
History
The electron as a unit of charge in electrochemistry had been posited by G. Johnstone Stoney in 1874. In 1894, he also invented the word itself.
The discovery that the electron was a subatomic particle was made in 1897 by J.J. Thomson at the Cavendish Laboratory at Cambridge University, while he was studying "cathode rays". Influenced by the work of James Clerk Maxwell, and the discovery of the X-ray, he deduced that cathode rays existed and were negatively charged "particles", which he called "corpuscles". He published his discovery in 1897.
The periodic law states that the chemical properties of elements largely repeat themselves periodically and is the foundation of the periodic table of elements. The law itself was initially explained by the atomic mass of the elements. However, as there were anomalies in the periodic table, efforts were made to find a better explanation for it. In 1913, Henry Moseley introduced the concept of the atomic number and explained the periodic law with the number of protons each element has. In the same year, Niels Bohr showed that electrons are the actual foundation of the table. In 1916, Gilbert Newton Lewis and Irving Langmuir explained the chemical bonding of elements by electronic interactions.
See also
- Standard model
- Subatomic particle
- Proton
- Positron
- Neutron
- Photoelectric Effect
- Lightning
- List of particles
- Cathode rays
- Electricity
- Fermion field
External links
- [http://www.aip.org/history/electron/ The Discovery of the Electron] from the American Institute of Physics History Center
- [http://pdg.lbl.gov/ Particle Data Group]
- Stoney, G. Johnstone, "[http://dbhs.wvusd.k12.ca.us/webdocs/Chem-History/Stoney-1894.html Of the 'Electron,' or Atom of Electricity]". Philosophical Magazine. Series 5, Volume 38, p. 418-420 October 1894.
- Eric Weisstein's World of Physics: [http://scienceworld.wolfram.com/physics/Electron.html Electron]
References
-
-
- Brumfiel, G. (6 January 2005). Can electrons do the splits? In Nature, 433, 11.
ko:전자
ja:電子
simple:Electron
th:อิเล็กตรอน
Magnet
A magnet is an object that has a magnetic field. The word magnet comes from the Greek "magnítis líthos" (μαγνήτης λίθος), which means "magnesian stone". Magnesia is an area in Greece (Now Manisa, Turkey) where deposits of magnetite have been discovered since antiquity.
Introduction
In the modern sense, a magnet is any material that has a magnetic field. It can be in the form of a permanent magnet or an electromagnet. Permanent magnets do not rely upon outside influences to generate their field. Electromagnets rely upon electric current to generate a magnetic field - when the current increases, so does the field. Magnets are attracted to or repelled by other things. If a magnet is strongly attracted to something, then that something is said to have a high permeability. Iron and steel are two examples of materials with very high permeability, and they are strongly attracted to magnets. Liquid oxygen is an example of something with a low permeability, and it is only weakly attracted to a magnetic field. Water has such a low permeability that it is actually repelled by magnetic fields. Everything has a measurable permeability: people, air and even the vacuum of space.
Physical origin of magnetism
Permanent Magnets
All normal matter is composed of particles (protons, neutrons, and electrons), and all of these particles have the fundamental property of quantum mechanical spin. Spin gives each one of these particles an associated magnetic field. Because of this, and the fact that the average macroscopic piece of matter contains huge numbers of these particles, it would be expected that all matter would be magnetic. Everyday experience shows that this is not the case.
Within each atom and molecule, the spin of each of these particles is highly ordered as a result of the Pauli Exclusion Principle. However, there is no long range ordering of these spins between atoms and molecules. Without long range ordering, there is no net magnetic field because the magnetic moment of each one of the particles is cancelled by the magnetic moment of other particles.
Permanent magnets are special in that long range ordering does exist. The highest degree of ordering exists within magnetic domains. These domains can be likened to microscopic neighbourhoods in which there is a strong reinforcing interaction between particles, and as a result, a great deal of order. The greater the degree of ordering within and between domains, the greater the resulting field will be.
Long range ordering (and the resulting strong net magnetic field) is one of the hallmarks of a ferromagnetic material.
More detail
Electrons play the primary role in generating a magnetic field. Within an atom, electrons can exist either individually or in pairs within any given orbital. When they are paired, the individuals in that pair always have opposite spin (one up, one down). The fact that the spins have opposite orientation means that the two cancel one another. If all electrons are paired, no net magnetic field will be generated.
In some atoms, there are electrons that are unpaired. All magnets have unpaired electrons, but not all atoms with unpaired electrons are ferromagnetic. In order for the material to become ferromagnetic, not only must there be unpaired electrons present, but those unpaired electrons must interact with one another over long ranges such that they are all oriented in the same way. The specific electron configuration of the atoms (as well as the distance between atoms) is what leads to this long range ordering. The electrons find that they can exist in a lower energy state if they all have the same orientation.
Electromagnets
electron configuration. There are four steel pole tips, two opposing magnetic north poles and two opposing magnetic south poles. The steel is magnetized by a large electric current that flows in the coils of tubing wrapped around the poles.]]
An electromagnet, in its simplest form, is a wire that has been coiled into one or more loops. This coil is known as a solenoid. When electric current flows along the coil, a magnetic field is generated around the coil. The orientation of this field can be determined via the right hand rule. The strength of the field is influenced by several factors, including:
- the number of loops
- the amount of current
- the material in the core
The more loops of wire and the greater the current, the stronger the field will be.
If the coil of wire is empty in the center, it will tend to generate a very weak field. Different ferromagnetic or paramagnetic items can be placed in the center of the core with the effect of magnifying the magnetic field, for example an iron nail (soft iron is commonly used for this purpose). The addition of these types of materials can result in a several hundred- to thousand-fold increase of field strength.
At long distances, magnetic fields obey an inverse square law. This means that the field strength is inversely proportional to the distance from the magnet. If the face of an electromagnet is machined to a high degree of precision, it will be able to get much closer to the surface it is trying to attract. Take the case of an electromagnet trying to attract an extremely smooth, flat metal plate. If the electromagnet's face is extremely smooth and flat as well, there will be many more points of contact with the plate, and so the magnetic circuit will have less resistance to the magnetic field.
Electromagnets find uses in many places, ranging from particle accelerators, to junkyard cranes, to MRI machines.
If an electromagnet is strong enough, the magnetic force between neighbouring loops of wire can cause the electromagnet to be crushed by its own magnetic field.
Characteristics of magnetic materials
Permanent magnets and dipoles
All magnets are dipoles: that is, all magnets have a north and a south pole. The poles are not a pair of things on or inside the magnet. They are a concept used to discuss and describe magnets. In the image at the top of this page, the poles look like specific locations (because the highest surface intensity of the field occurs at the poles), but this does not mean that they are specific locations.
To understand the concept of pole, imagine a row of people who are all facing the same direction and standing in line. While there is a "face" end of the line and a "back" end of the line, there is no one place where all of the faces are and all of the backs are. The person at the front of the face end has a back; and the person at the back end has a face. If you divide the line into two shorter lines, each one of the shorter lines still has a face end and a back end. Even if you pull the line completely apart so that there are just individuals standing around, each one of the individuals still has a face and a back. This can continue without end.
The same holds true with magnets. There is not one place where all of the north or south poles are. If a magnet is divided in two, two magnets will result--and both magnets will have a north and a south pole. Those smaller magnets can then be divided, and all of the resulting pieces will have both a north and south pole. In most instances, if the material continues to be broken into smaller and smaller pieces there will be a point where the pieces are too small to retain a net magnetic field. They won't become individual north or south poles though; instead, they will just lose the ability to maintain a net field. Some materials, however, can be divided down to the molecular level and still maintain a net field with both a north and a south pole. There are theories involving the possibility of north and south magnetic monopoles, but no magnetic monopole (single pole) has ever been found.
North/south pole designation and the Earth's magnetic field
A standard naming system for the poles of magnets is important. Historically, the terms north and south reflect awareness of the relationship between magnets and the earth's magnetic field. A freely suspended magnet will eventually orient itself north-to-south, because of its attraction to the north and south magnetic poles of the earth. The end of a magnet that points toward the Earth's geographic North Pole is labeled as the north pole of the magnet; correspondingly, the end that points south is the south pole of the magnet.
The Earth's current geographic north is thus actually its magnetic south. Confounding the situation further, it is known that the Earth's magnetic field has reversed itself in the past, so this system of naming is likely to be backward at some time in the future (see Earth's magnetic field).
Fortunately, by using an electromagnet and the right hand rule, the orientation of the field of a magnet can be defined without reference to the Earth's geomagnetic field.
To avoid the confusion between geographic and magnetic north and south poles, the terms positive and negative are sometimes used for the poles of a magnet. The positive pole is that which seeks geographical north.
Common uses for magnets
- Magnetic recording media: Common VHS tapes contain a reel of magnetic tape. The information that makes up the video and sound is encoded on the magnetic coating on the tape. This is why magnets will destroy the information in these types of tapes. Common audio cassettes also rely on magnetic tape. Similarly, in computers, floppy disks and hard disks record data on a thin magnetic coating.
- Credit, debit, and ATM cards: All of these cards have a magnetic strip on one of their sides. This strip contains the necessary information to contact an individuals financial institution and connect with their account(s).
- Common televisions and computer monitors: The vast majority of TV's and computer screens rely in part on an electromagnet to generate an image--see the article on cathode ray tubes for more information. Plasma screens and LCDs rely on different technology entirely.
- Loudspeakers and microphones: Loudspeakers actually rely on a combination of a permanent magnet and an electromagnet. A speaker is fundamentally a device to convert electric energy (the signal) into mechanical energy (the sound). The electromagnet carries the signal, which generates a changing magnetic field that pushes and pulls on the field generated by the permanent magnet. This pushing and pulling moves the cone, which creates sound. Not all speakers rely on this technology, but the vast majority do. Standard microphones are based upon the same concept, but run in reverse. A microphone has a cone or membrane attached to a coil of wire. The coil rests inside a specially shaped magnet. When sound vibrates the membrane, the coil is vibrated as well. As the coil moves through the magnetic field, a voltage is generated in the coil (see Lenz's Law). This voltage in the wire is now an electric signal that is representative of the original sound.
- Electric motors and generators: Some electric motors (much like loudspeakers) rely upon a combination of an electromagnet and a permanent magnet, and much like loudspeakers, they convert electric energy into mechanical energy. A generator is the reverse: it converts mechanical energy into electric energy.
- Transformers: Transformers are devices that transfer electric energy between two devices that are electrically disconnected via magnetic coupling.
- Chucks: Chucks are used in the metalworking field to hold objects. If these objects can be held securely with a magnet then a permanent or electromagnetic chuck may be used. Magnets are also used in other types of fastening devices, such as the magnetic base, the magnetic clamp and the refrigerator magnet.
How to magnetize materials
Ferromagnetic materials can be magnetised in the following ways:
- Placing the item in an external magnetic field will result in the item retaining some of the magnetism on removal. Vibration has been shown to increase the effect. Ferrous materials aligned with the earth's magnetic field and which are subject to vibration (eg frame of a conveyor) have been shown to aquire significant residual magnetism.
- Placing the item in a solenoid with a direct current passing through it.
- Stroking - An existing magnet is moved from one end of the item to the other repeatedly in the same direction.
How to demagnetize materials
Permanent magnets can be demagnetized in the following ways:
- Heat. Heating a magnet past its Curie point will destroy the long range ordering.
- Contact. Stroking one magnet with another in random fashion will demagnetize the magnet being stroked, in some cases; some materials have a very high coercive field and cannot be demagnetized with other permanent magnets.
- Hammering or jarring. Such activity will destroy the long range ordering within the magnet.
- Being placed in a solenoid which has an alternating current being passed through it. The alternating current will disrupt the long range ordering, in much the same way that direct current can cause ordering.
In an electromagnet, ceasing the flow of current will eliminate the magnetic field. However, a slight field may remain in the core material as a result of hysteresis.
Types of permanent magnets
- Rare Earth or Neodymium Magnets, which are some of the most powerful permanent magnets
- Samarium-Cobalt Magnets
- Ceramic Magnets
- Plastic Magnets
- Alnico Magnets
Magnetic forces
Magnetized items interact with other items in very specific ways.
Magnets and other magnets
If a magnet is brought close enough to another magnet, their fields will begin to interact in the following ways:
- If each magnets north pole is brought together, the magnets will repel one another (like poles repel)
- If the north pole of one magnet is brought to the south pole of the other magnet (or vice versa), the magnets will attract one another (opposite poles attract)
Magnets and ferromagnetic materials
If a magnet is brought close enough to a ferromagnetic material (that is not magnetized itself), the magnet will strongly attract the ferromagnetic material regardless of orientation. Both the north and south pole of the magnet will attract the other item with equal strength.
Magnets and diamagnetic materials
By definition, diamagnetic materials weakly repel a magnetic field. This occurs regardless of the north/south orientation field.
Magnets and paramagnetic materials
By definition, paramagnetic materials are weakly attracted to a magnetic field. This occurs regardless of the north/south orientation of the field.
Calculating the magnetic force
Calculating the attractive or repulsive force between two magnets is, in the general case, an extremely complex operation, as it depends on the shape, magnetization, orientation and separation of the magnets. However, a formula exists for the simple case of the force between two magnetic poles:
: [http://geophysics.ou.edu/gravmag/mag_basic/mag_basic.html]
where
:F is force (SI unit: newton)
:m is pole strength (SI unit: weber)
:μ is the permeability of the intervening medium (SI unit: tesla meter per ampere)
:r is the separation (SI unit: meter).
See also
- electromagnet
- electromagnetism
- electromagnetic field
- neodymium magnet
- diamagnetism
- magnetic dipole
- magnetic monopole
- magnetism
- molecular magnet
- paramagnetism
- single-molecule magnet
Online references
- [http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html HyperPhysics E/M], good complete tree diagram of electromagnetic relationships with magnets
- [http://www.arnoldmagnetics.com/mtc/index.htm Magnet Education] and [http://www.magnetsales.com/Design/DesignG.htm Understanding Commercial Magnets] useful companies who have many helpful magnet equations
- [http://en.wikipedia.org/wiki/Maxwell%27s_equations Maxwell's Equations] and some history...
- [http://www.oz.net/~coilgun/theory/home.htm Detailed Theory on Designing a Solenoid] or a Coil Gun
- [http://www.makeitlouder.com/High%20Technology.html Help on designing magnet systems]
Printed references
- "positive pole n." The Concise Oxford English Dictionary. Ed. Catherine Soanes and Angus Stevenson. Oxford University Press, 2004. Oxford Reference Online. Oxford University Press.
External articles
- Joseph J. Stupak Jr., "[http://oersted.com/magnetizing.PDF Methods of Magnetizing Permanent Magnets]". Oersted Technology at the EMCW Coil Winding Show, 2000. (PDF)
Category:Magnets
ja:磁石
Nitric oxide
The chemical compound nitric oxide is a gas with chemical formula NO. It is an important signaling molecule in the body of mammals including humans, one of the few gaseous signaling molecules known. It is also a toxic air pollutant produced by automobile engines and power plants.
Nitric oxide (NO) should not be confused with nitrous oxide (N2O), a general anaesthetic, or with nitrogen dioxide (NO2) which is another poisonous air pollutant.
The nitric oxide molecule is a free radical which makes it very reactive and unstable. In air, it quickly reacts with oxygen to form the poisonous nitrogen dioxide.
Production and environmental effects
At high temperatures molecular nitrogen and oxygen can combine to form nitric oxide. A major natural source is lightning. Human activity has drastically increased the production of nitric oxide in combustion chambers. One purpose of catalytic converters in cars is to partially reverse this reaction.
Nitric oxide in the air may later convert to nitric acid which has been implicated in acid rain. Furthermore, both NO and NO2 participate in ozone layer depletion.
Technical applications
Nitric oxide has few industrial uses. It is an intermediate of the Ostwald process which converts ammonia into nitric acid.
Nitric oxide can be used for detecting surface radicals on polymers. Quenching of surface radicals with nitric oxide results in incorporation of nitrogen, which can be quantified by means of X-ray photoelectron spectroscopy.
A very small amount (0.03%) of nitric oxide can be added to the shielding gas used in GTAW welding, in order to minimize the formation of ozone, which is a health risk if inhaled.
Because of its production in allergic reactions, there is research on using levels of exhaled nitric oxide to optimize treatment for asthma.
Biological functions
See also: Endothelium-derived relaxing factor (EDRF) and signal transduction
In the body, nitric oxide is synthesized from arginine and oxygen by various nitric oxide synthase (NOS) enzymes.
The endothelium (inner lining) of blood vessels use nitric oxide to signal the surrounding smooth muscle to relax, thus dilating the artery and increasing blood flow. This underlies the action of nitroglycerin, amyl nitrate and other nitrate derivatives in the treatment of heart disease: the compounds are converted to nitric oxide (by a process that is not completely understood) which in turn dilates the coronary artery (blood vessels around the heart), thereby increasing its blood supply. Nitric oxide also plays a role in erection of the penis, and explains the mechanism of sildenafil (Viagra®). The effects of the recreational drugs known as poppers are also thought to be due to nitric oxide.
Macrophages, certain cells of the immune system, produce nitric oxide in order to kill invading bacteria. Under certain conditions, this can backfire: fulminant infection (sepsis) causes excess production of nitric oxide by macrophages, leading to vasodilatation (widening of blood vessels) and probably being one of the main causes of hypotension (low blood pressure) in sepsis.
Nitric oxide also serves as a neurotransmitter between nerve cells. Unlike most other neurotransmitters that only transmit information from a presynaptic to a postsynaptic neuron, the small nitric oxide molecule can diffuse all over and can thereby act on several nearby neurons, even on those not connected by a synapse. It is conjectured that this process may be involved in memory through the maintenance of long-term potentiation.
Production of NO also plays a role in development and maintenance of erection by stimulating PDE5-related intracellular cGMP in the smooth muscle cells surrounding the blood vessels supplying the corpus cavernosum; through relaxation of these muscles, more blood can flow in.
The discovery of the biological functions of nitric oxide in the 1980s came as a complete surprise and caused quite a stir. Nitric oxide was named "Molecule of the Year" in 1992 by the journal Science, a Nitric Oxide Society was founded, and a scientific journal devoted entirely to nitric oxide was created. The Nobel Prize in Physiology or Medicine in 1998 was awarded to Ferid Murad, Robert F. Furchgott, and Louis Ignarro for the discovery of the signalling properties of nitric oxide. It is estimated that yearly about 3,000 scientific articles about the biological roles of nitric oxide are published.
Measurement of nitric oxide
Nitric oxide can be measured using a simple chemiluminescent reaction involving ozone.
A sample containing nitric oxide is mixed with a large quantity of ozone. The nitric oxide reacts with the ozone to produce oxygen and nitrogen dioxide. This reaction also produces light (chemiluminescence) which can be measured using a photodetector. The amount of light produced is proportional to the amount of nitric oxide in the sample.
: NO + O3 → NO2 + O2 + light
There are other methods of testing, including electrochemical methods, where nitric oxide in a test sample reacts to produce a current or voltage difference on a surface.
External links
- [http://www.elsevier.com/inca/publications/store/6/2/2/9/2/6/ Nitric Oxide: Biology and Chemistry], peer reviewed scientific journal
- [http://www.nobel.se/medicine/laureates/1998/index.html 1998 Nobel Prize in Physiology/Medicine for discovery of NO's role in cardiovascular regulation]
Category:OxidesCategory:Nitrogen compounds
Category:NeurotransmittersCategory:Nitrogen metabolism
ja:一酸化窒素
Chlorine dioxide
Chlorine dioxide is a reddish-yellow gas which is one of several known oxides of chlorine. Chlorine dioxide is relatively stable in the gas and liquid states, but can explode easily. Practically, it is never handled in its pure form.
Uses
Chlorine dioxide is used in the disinfection of water and bleaching of flour and wood pulp. It can also be used for air disinfection, and was the principal agent used in the decontamination of buildings in the United States after the 2001 anthrax attacks. It is effective against < | | |
