In chemistry, valence bond theory is one of the two basic theories, along with molecular orbital theory, that were developed to use the methods of quantum mechanics to explain chemical bonding. It focuses on how the atomic orbitals of the dissociated atoms combine to give individual chemical bonds when a molecule is formed. In contrast, molecular orbital theory has orbitals. In 1916, G. N. Lewis proposed that a chemical bond forms by the interaction of two shared bonding electrons, with the representation of molecules as Lewis structures. In 1927 the Heitler–London theory was formulated which for the first time enabled the calculation of bonding properties of the hydrogen molecule H2 based on quantum mechanical considerations. Walter Heitler determined how to use Schrödinger's wave equation to show how two hydrogen atom wavefunctions join together, with plus and exchange terms, to form a covalent bond, he called up his associate Fritz London and they worked out the details of the theory over the course of the night.
Linus Pauling used the pair bonding ideas of Lewis together with Heitler–London theory to develop two other key concepts in VB theory: resonance and orbital hybridization. According to Charles Coulson, author of the noted 1952 book Valence, this period marks the start of "modern valence bond theory", as contrasted with older valence bond theories, which are electronic theories of valence couched in pre-wave-mechanical terms. Linus Pauling published in 1931 his landmark paper on valence bond theory: "On the Nature of the Chemical Bond". Building on this article, Pauling's 1939 textbook: On the Nature of the Chemical Bond would become what some have called the bible of modern chemistry; this book helped experimental chemists to understand the impact of quantum theory on chemistry. However, the edition in 1959 failed to adequately address the problems that appeared to be better understood by molecular orbital theory; the impact of valence theory declined during the 1960s and 1970s as molecular orbital theory grew in usefulness as it was implemented in large digital computer programs.
Since the 1980s, the more difficult problems, of implementing valence bond theory into computer programs, have been solved and valence bond theory has seen a resurgence. According to this theory a covalent bond is formed between two atoms by the overlap of half filled valence atomic orbitals of each atom containing one unpaired electron. A valence bond structure is similar to a Lewis structure, but where a single Lewis structure cannot be written, several valence bond structures are used; each of these VB structures represents a specific Lewis structure. This combination of valence bond structures is the main point of resonance theory. Valence bond theory considers that the overlapping atomic orbitals of the participating atoms form a chemical bond; because of the overlapping, it is most probable. Valence bond theory views bonds as weakly coupled orbitals. Valence bond theory is easier to employ in ground state molecules; the inner-shell orbitals and electrons remain unchanged during the formation of bonds.
The overlapping atomic orbitals can differ. The two types of overlapping orbitals are pi. Sigma bonds occur. Pi bonds occur. For example, a bond between two s-orbital electrons is a sigma bond, because two spheres are always coaxial. In terms of bond order, single bonds have one sigma bond, double bonds consist of one sigma bond and one pi bond, triple bonds contain one sigma bond and two pi bonds. However, the atomic orbitals for bonding may be hybrids; the bonding atomic orbitals have a character of several possible types of orbitals. The methods to get an atomic orbital with the proper character for the bonding is called hybridization. Modern valence bond theory now complements molecular orbital theory, which does not adhere to the valence bond idea that electron pairs are localized between two specific atoms in a molecule but that they are distributed in sets of molecular orbitals which can extend over the entire molecule. Molecular orbital theory can predict magnetic and ionization properties in a straightforward manner, while valence bond theory gives similar results but is more complicated.
Modern valence bond theory views aromatic properties of molecules as due to spin coupling of the π orbitals. This is still the old idea of resonance between Kekulé and Dewar structures. In contrast, molecular orbital theory views aromaticity as delocalization of the π-electrons. Valence bond treatments are restricted to small molecules due to the lack of orthogonality between valence bond orbitals and between valence bond structures, while molecular orbitals are orthogonal. On the other hand, valence bond theory provides a much more accurate picture of the reorganization of electronic charge that takes place when bonds are broken and formed during the course of a chemical reaction. In particular, valence bond theory predicts the dissociation of homonuclear diatomic molecules into separate atoms, while simple molecular orbital theory predicts dissociation into a mixture of atoms and ions. For example, the molecular orbital function for dihydrogen is an equal mixture of the covalent and ionic valence bond structures and so predicts incorrectly that the molecule would dissociate into an equal mixture of hydrogen atoms and hydrogen positive and negative ions.
Modern valence bond theory replaces the overlapping atomic orbitals by overlapping valence bond orbitals that are expanded over a large number of basis functions, either ce
Tanya Biank is an American journalist and speaker. She has written two books, one of, the inspiration for the television show, Army Wives. Biank comes from a family of active-duty service members, her father was in the United States Army. He served for 33 years, her sister, Lieutenant Colonel Maria Biank, was deployed to Iraq in 2009, the same time as Tanya Biank's husband. Biank graduated from Herndon High School in 1989, she attended Pennsylvania State University. She graduated in 1993. After college, Biank lived in Korea for one year, she studied language and culture, while teaching English as a second language at an all-girls school. Besides Korea, Biank has lived in a variety of places including, Fort Knox in Kentucky, New York, Northern Virginia, Georgia. Biank is a Fulbright Scholar. Biank traveled around the world with the troops, she was a former news reporter for the Fayetteville Observer. Her coverage of the Fort Bragg Murders in 2002 led to Congressional inquiries and changes in Army policies.
She is a syndicated columnist and contributing writer to various military-related publications: Operation Homefront, Military Spouse Magazine, Military Officer Magazine. Her work has appeared in The New York Times and The Wall Street Journal. Biank has been a guest on numerous television and radio outlets including, Good Morning, America, CNN, Fox News, MSNBC, ABC News, NPR. Biank has written two books, her first, Army Wives: The Unwritten Code of Military Marriage, was titled, Under the Sabers: The Unwritten Code of Army Wives. It inspired the Lifetime television series Army Wives, she wrote the book, Undaunted: The Real Story of America's Servicewomen in Today's Military. Biank's story, "Having it All," was published in Stories Around the Table: Laughter and Strength in Military Life, she is inspired by her personal experiences. Beyond writing, Biank served as a leader of a Family Readiness Group during her husband's 2009-2010 deployment to Iraq; this organization was formed to help families face the difficult challenges of military life.
She is a member of the Society of Daughters of the U. S. Army. Biank is married to Colonel Michael A. Marti, they have two children. Tanya Biank website Tanya Biank interview at Hispanic.com Tanya Biank interview at veterans Journal Tanya Biank bio at Penguin Tanya Biank: Why would a woman join the military? at Penguin blog Appearances on C-SPAN
The 2013 Detroit Lions season was the franchise's 84th season in the National Football League, their 80th as the Detroit Lions, as well as the fifth and final under head coach Jim Schwartz, fired on December 30. It was the final season under the ownership of William Clay Ford, Sr. who died in March 2014. The Lions improved upon their 4–12 record from 2012 when they defeated the Dallas Cowboys in Week 8 to go to 5–3 on the season, their divisional record improved from 2012. At the end of Week 10, the Lions were in first place in their division following their first win at Soldier Field since 2007. With their Thanksgiving Day win over the Green Bay Packers, the Lions not only won their first Thanksgiving Day game since 2003, but they went undefeated in division home games for the first time since 1999; the Lions dropped to 3rd place after their loss to the Ravens in Week 15, they were eliminated from postseason contention after their loss to the New York Giants six days later. They lost their last game as well, ending the season at 7–9.
Notes The Lions traded their original fourth-round selection along with a 2012 seventh-round selection to the Minnesota Vikings in exchange for the Vikings' 2012 fifth- and seventh-round selections. The Lions received two compensatory selections -- Nos. 245 overall. Note: Intra-division opponents are in bold; the Vikings scored first, quickly. After the Lions failed on a field goal attempt when new punter/holder Sam Martin fumbled the snap, the Vikings took over on their own 22. On the first play from scrimmage, Adrian Peterson scampered 78 yards for a touchdown. David Akers made it 7–3 on a 33-yard field goal, though the Lions missed out on seven points that series when a touchdown reception by Calvin Johnson was reversed. In the second quarter, Akers connected on a 42-yard field goal to make the score 7–6; the Vikings responded with a 65-yard touchdown drive, capped by a 4-yard TD run from Peterson, to go up 14–6. The Lions closed the gap late in the half when Joique Bell finished off a 70-yard drive with a 1-yard run to make it 14–13.
Bell plunged over from the 1-yard line again in the third quarter to put the Lions up for the first time in the game, 20–14. The Vikings' Blair Walsh narrowed the lead to 20–17 with a 52-yard field goal; the Lions went up 27–17 when Matthew Stafford and new acquisition Reggie Bush connected on a 77-yard pass play. Adrian Peterson scored his third touchdown of the day, on a 4-yard pass from Christian Ponder, to put the Vikings within 3 points again, 27–24; the Lions would get the only score of the fourth quarter, a 1-yard touchdown pass from Stafford to rookie tight end Joseph Fauria, making the final score Detroit 34, Minnesota 24. Reggie Bush had 191 yards from scrimmage on the afternoon, while Matthew Stafford was 28-of-43 passing for 357 yards, two touchdowns and one interception. After Adrian Peterson's opening 78-yard run, the Lions defense held him to just 15 yards on 17 carries. After a scoreless first quarter, the Cardinals struck first on a Jay Feely 47-yard field goal; the Lions responded with a 72-yard touchdown pass from Matthew Stafford to Calvin Johnson, to take a 7–3 lead.
The Cardinals went up 10–7 on a 36-yard TD pass from Carson Palmer to Andre Ellington. The Lions retook the lead, 14–10, when Stafford and Johnson connected again, this time on a 3-yard TD pass. Arizona scored first in the third quarter, capitalizing on a Lions turnover with a 23-yard Jay Feely field goal; the Lions got a turnover of their own, as DeAndre Levy returned an interception 66 yards for a touchdown, making the score 21–13. The Cardinals finished the third quarter scoring with a 43-yard Feely field goal to close the score to 21–16. Feely hit again from 33 yards early in the fourth quarter to make the score 21–19. A pass interference penalty by Bill Bentley put the ball on the Lions 1-yard line late in the final quarter, Arizona's Rashard Mendenhall plunged over two plays for a touchdown. Arizona failed on a 2-point conversion, making the final score Cardinals 25, Lions 21. Matthew Stafford was 24-of-36 passing for two touchdowns. Calvin Johnson led all receivers with 6 receptions for two touchdowns.
David Akers missed a 47-yard field goal, had another field goal attempt blocked. Washington took a 7–0 lead in the first quarter when DeAngelo Hall intercepted a Matthew Stafford pass and returned it 17 yards for a touchdown. Detroit tied it on the next possession, when Joique Bell capped an 85-yard drive with a 12-yard TD run. Early in the second quarter, Stafford hit tight end Joseph Fauria with a 5-yard TD pass, putting the Lions up 14–7. A 72-yard Redskins scoring drive was punctuated by an Alfred Morris 30-yard TD run, knotting the score at 14–14. Near the end of the first half, David Akers connected on a 32-yard field goal, sending the Lions to the locker room with a 17–14 lead; the only score of the third quarter came on a John Potter 43-yard field goal, tying the score again at 17–17. The Lions went up 20–17 early in the fourth quarter on a 28-yard field goal from Akers; the Redskins appeared to take the lead on a 57-yard TD pass from Robert Griffin III to Aldrick Robinson, but the play was reversed when replays revealed that Robinson did not maintain possession of the ball when he tumbled to the ground.
The Lions took advantage on their next drive, when Stafford hit Calvin Johnson with an 11-yard TD pass, increasing the lead to 27–17. The Redskins got a late 21-yard field goal from John Potter to close the gap to 27–20, but could not gain possession on the ensuing onside kickoff. Matthew Stafford passed for two touchdowns on the day. Nate Burleson led all receivers with 116 yards, while Calvin Johnson tallied 115 re