Covalent bond

A covalent bond called a molecular bond, is a chemical bond that involves the sharing of electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs, the stable balance of attractive and repulsive forces between atoms, when they share electrons, is known as covalent bonding. For many molecules, the sharing of electrons allows each atom to attain the equivalent of a full outer shell, corresponding to a stable electronic configuration. In organic chemistry, covalent bonds are much more common than ionic bonds. Covalent bonding includes many kinds of interactions, including σ-bonding, π-bonding, metal-to-metal bonding, agostic interactions, bent bonds, three-center two-electron bonds; the term covalent bond dates from 1939. The prefix co- means jointly, associated in action, partnered to a lesser degree, etc.. In the molecule H2, the hydrogen atoms share the two electrons via covalent bonding. Covalency is greatest between atoms of similar electronegativities. Thus, covalent bonding does not require that the two atoms be of the same elements, only that they be of comparable electronegativity.

Covalent bonding that entails sharing of electrons over more than two atoms is said to be delocalized. The term covalence in regard to bonding was first used in 1919 by Irving Langmuir in a Journal of the American Chemical Society article entitled "The Arrangement of Electrons in Atoms and Molecules". Langmuir wrote that "we shall denote by the term covalence the number of pairs of electrons that a given atom shares with its neighbors."The idea of covalent bonding can be traced several years before 1919 to Gilbert N. Lewis, who in 1916 described the sharing of electron pairs between atoms, he introduced the Lewis notation or electron dot notation or Lewis dot structure, in which valence electrons are represented as dots around the atomic symbols. Pairs of electrons located between atoms represent covalent bonds. Multiple pairs represent multiple bonds, such as triple bonds. An alternative form of representation, not shown here, has bond-forming electron pairs represented as solid lines. Lewis proposed.

In the diagram of methane shown here, the carbon atom has a valence of four and is, surrounded by eight electrons, four from the carbon itself and four from the hydrogens bonded to it. Each hydrogen has a valence of one and is surrounded by two electrons – its own one electron plus one from the carbon; the numbers of electrons correspond to full shells in the quantum theory of the atom. While the idea of shared electron pairs provides an effective qualitative picture of covalent bonding, quantum mechanics is needed to understand the nature of these bonds and predict the structures and properties of simple molecules. Walter Heitler and Fritz London are credited with the first successful quantum mechanical explanation of a chemical bond in 1927, their work was based on the valence bond model, which assumes that a chemical bond is formed when there is good overlap between the atomic orbitals of participating atoms. Atomic orbitals have specific directional properties leading to different types of covalent bonds.

Sigma bonds are the strongest covalent bonds and are due to head-on overlapping of orbitals on two different atoms. A single bond is a σ bond. Pi bonds are due to lateral overlap between p orbitals. A double bond between two given atoms consists of one σ and one π bond, a triple bond is one σ and two π bonds. Covalent bonds are affected by the electronegativity of the connected atoms which determines the chemical polarity of the bond. Two atoms with equal electronegativity will make nonpolar covalent bonds such as H–H. An unequal relationship creates a polar covalent bond such as with H−Cl; however polarity requires geometric asymmetry, or else dipoles may cancel out resulting in a non-polar molecule. There are several types of structures for covalent substances, including individual molecules, molecular structures, macromolecular structures and giant covalent structures. Individual molecules have strong bonds that hold the atoms together, but there are negligible forces of attraction between molecules.

Such covalent substances are gases, for example, HCl, SO2, CO2, CH4. In molecular structures, there are weak forces of attraction; such covalent substances are low-boiling-temperature liquids, low-melting-temperature solids. Macromolecular structures have large numbers of atoms linked by covalent bonds in chains, including synthetic polymers such as polyethylene and nylon, biopolymers such as proteins and starch. Network covalent structures contain large numbers of atoms linked in sheets, or 3-dimensional structures; these substances have high melting and boiling points, are brittle, tend to have high electrical resistivity. Elements that have high electronegativity, the ability to form three or four electron pair bonds form such large macromolecular structures. Bonds with one or three electrons can be found in radical species, which have an odd number of electrons; the simplest example of a 1-electron bond is found in the dihydrogen cation, H+2. One-electron bonds have about half the bond energy of

Kevin Eubanks

Kevin Tyrone Eubanks is an American jazz and fusion guitarist and composer. He was the leader of The Tonight Show Band with host Jay Leno from 1995 to 2010, he led the Primetime Band on the short-lived The Jay Leno Show. Eubanks was born into a musical family, his mother, Vera Eubanks, is classical pianist and organist. His uncle, Ray Bryant, was a jazz pianist, his older brother, Robin Eubanks, is a trombonist, his younger brother Duane Eubanks is a trumpeter. Two cousins are musicians, the late bassist David Eubanks and the pianist Charles Eubanks. Kevin studied trumpet before settling on the guitar; as an elementary school student, Eubanks was trained in violin and piano at the Settlement Music School in Philadelphia. He attended Berklee College of Music in Boston and moved to New York to begin his professional career. Eubanks is a pescetarian and maintains a diet of fresh fruits, grains, egg whites, fish, he is an avid fan of Philadelphia sports teams. He once lost a bet on the Philadelphia 76ers, he was forced to eat a corn dog when he lost.

In 2007, he was voted PETA's "World's Sexiest Vegetarian Man". After Eubanks moved to New York, he began performing with noted jazzmen such as Art Blakey, Roy Haynes, Slide Hampton and Sam Rivers. Like his brother Robin, he has played on record with double bassist Dave Holland. In 1983, while continuing to perform with others, he formed his own quartet, playing gigs in Jordan and India on a tour sponsored by the U. S. State Department, his first recording as a leader, was released on the Elektra label when Eubanks was 25 years old. It led to four albums for Blue Note. In total, Eubanks has appeared on over 100 albums. In 2001, he founded the label Insoul Music. Eubanks has taught at the Banff School of Fine Arts in Canada, at Rutgers University, at the Charlie Parker School in Perugia, Italy. In 2005, Eubanks received an honorary doctorate degree from his alma mater, Berklee College of Music, he is a member of Kappa Alpha Psi fraternity and has served as an active member of the Artistic Advisory Panel of the BMI Foundation since 1999.

In 1992, Eubanks moved to the West Coast to play guitar in The Tonight Show Band. He composed "Kevin's Country," the closing theme music for The Tonight Show with Jay Leno. In 1995, he replaced Branford Marsalis as leader of the band; when NBC moved Leno's show from late night to prime time, Eubanks moved with the band to continue conducting music for the short-lived The Jay Leno Show. Eubanks appeared on the new show as The Primetime Band. On April 12, 2010, Eubanks announced on the show that he would be leaving The Tonight Show following its 18th season, his last show was on Friday, May 28, 2010. He indicated in an interview with The Philadelphia Inquirer that he wanted to concentrate on music, adding that his leaving was not provoked by any problems with Leno or NBC. Following his departure from The Tonight Show, he began touring with bandmate Marvin "Smitty" Smith on drums and Bill Pierce on saxophone. On his website, Eubanks states his preference for Abe Rivera guitars, Mesa/Boogie amplifiers and D'Addario guitar strings.

Guitarist Sundance Opening Night Face to Face Heat of Heat Shadow Prophets The Searcher Promise of Tomorrow Turning Point Spirit Talk Live at Bradley's Spirit Talk 2 – Revelations Zen Food The Messenger Duets with Stanley Jordan East West Time Line Art Blakey and the Jazz Messengers − Live at Montreux and Northsea Steve Arrington's Hall of Fame − Steve Arrington's Hall Of Fame, Vol.1 The Young Lions Urszula Dudziak − Sorrow Is Not Forever... But Love Is James Williams − Alter Ego Kirk Lightsey Trio with Chet BakerEverything Happens to Me Oliver Lake Quintet − Expandable Language Billy HartOshumare Meredith D'Ambrosio − It's Your Dance James Williams Sextet − Progress Report The Mike Gibbs Orchestra − Big Music Billy Hart − Rah Robin Eubanks − Different Perspectives Dave Holland Quartet − Extensions Greg OsbySeason of Renewal Gary Thomas − While the Gate Is Open Gary Thomas − The Kold Kage Robin Eubanks − Karma Kirk Lightsey Trio − From Kirk to Nat Steve ColemanRhythm in Mind Harold Mabern – The Leading Man Ralph Moore – Round Trip Jean-Luc PontyNo Absolute Time Adam Rudolph's Moving Pictures − Skyway Dianne Reeves − That Day Terri Lyne CarringtonJazz Is a Spirit Carmen LundyMoment to Moment Dave Holland − Prism Orrin Evans - #knowingishalfthebattle Jazz Bridge Official Website Kevin Eubanks on IMDb Kevin Eubanks Acoustic on YouTube Kevin Eubanks' Vegetarianism Kevin Eubanks at The Interviews: An Oral History of Television

Nicholson River (Western Australia)

The Nicholson River is a river in the Kimberley region of Western Australia. It takes its name from the Nicholson Plains, named in 1879 by Alexander Forrest after Sir Charles Nicholson, the central figure in the circle of Australian'colonists' in London, a promoter of the Forrest brothers' explorations. In 1870 Nicholson had presented a paper entitled On Forrest's Expedition into the Interior of Western Australia, Goyder's Survey of the Neighbourhood of Port Darwin, on the Recent Progress of Australian Discovery to a meeting of the Royal Geographical Society of London; the river rises just north of Koolerong Bore flows south-west through Nicholson and through Marella Gorge turning north and discharging into the Ord River on the eastern edge of Purnululu National Park near Doughboy Hill. There are eleven tributaries of the Nicholson including.