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Topic: Valence bond theory

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	Valence bond theory - Wikipedia, the free encyclopedia
		Valence bond theory considers that the overlapping atomic orbitals of the participating atoms form a chemical bond.
		Valence bond theory is typically easier to employ in ground state molecules.
		Valence bond theory now complements Molecular Orbital Theory (MO theory), which does not adhere to the VB 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.
	en.wikipedia.org /wiki/Valence_bond_theory (486 words)

	Valence Bond Theory
		Valence bond theory was developed to describe where the shared electrons of two or more chemically bonded atoms would most likely be at any given moment in time.
		Valence bond theory assumes that the bond is weakly coupled orbitals with only a slight overlap.
		Valence bond theory explains more about the way atoms bond together than theories dealing with ionic bond, but it does not explain everything.
	www.iscid.org /encyclopedia/Valence_Bond_Theory (211 words)

	Valence Bond Thoery
		Valence Bond Theory was developed by Linus Pauling and others in the late 1930's to explain bonding and molecular geometry with one underlining theory.
		Using the valence bond approach, the geometry of the molecule is determined by which "hybrid" atomic orbitals form the hybrid orbital set used by any particular atom for bonding.
		to describe molecular bonding using valence bond concepts of hybridized atomic orbitals and bonds arising from the mutual"overlap" of atomic and/or hybrid orbitals.
	www.csubak.edu /~mdutton/u8c211.html (757 words)

	BBC - h2g2 - Valence Bond Theory of Chemical Bonding
		The chemical bond is of central importance to all branches of chemistry.
		The deficiencies in valence bond theory can be overcome by the introduction of the combined effects of promotion (excitation of an electron to a higher energy orbital) and hybridisation (the merging of the two or more atomic orbitals of the same atom in the excited state).
		Valence bond theory provides an adequate rationalisation for many aspects of molecular structure and bonding through the reduction in energy on the pairing of the unpaired electrons of constituent atoms.
	www.bbc.co.uk /dna/h2g2/A1011871 (3111 words)

	The Chemical Bond - Molecular Geometry
		One further feature of this theory is that it may be used to predict (or in some cases, rationalize) the observed geometries of molecules By the geometry of a molecule we mean the relative arrangement of the nuclei in three-dimensional space.
		The valence bond theory of the water molecule describes the two O—H bonds as resulting from the overlap of the H 1s orbitals with the two half-filled 2p orbitals of the oxygen atom.
		bond whose density is concentrated in the x-y plane, with a node in the x-z plane.
	www.chemistry.mcmaster.ca /esam/Chapter_6/section_4.html (2265 words)

	SparkNotes: Organic Molecular Orbitals: Valence Bond Theory
		Valence bond theory (VB) is a straightforward extension of Lewis structures.
		Valence bond theory says that electrons in a covalent bond reside in a region that is the overlap of individual atomic orbitals.
		In order to understand the limitations of valence bond theory, first we must digress to discuss molecular geometry, which is the spatial arrangement of covalent bonds around an atom.
	www.sparknotes.com /chemistry/organic1/orbitals/section1.html (966 words)

	Bonding (Site not responding. Last check: 2007-11-06)
		Ionic bonds are found between a metallic atom, which tends to lose electrons, and a nonmetallic atom, which tends to gain electrons.
		There are two complementary theories to account for this kind of bonding, valence bond theory and molecular orbital theory.
		The valence bond theory was originally formulated by G.
	home.att.net /~v.d.singleton/genchem/bonding.htm (2305 words)

	Valence Bond and MO models
		Linus Pauling became the champion of the valence bond model, which is easier to visualize and use.
		One of the problems that Pauling encountered early in his pioneering efforts with valence bond theory is clearly exemplified by a simple valence bond picture of the bonding in water.
		This picture shows clearly that the bond angle in water should be 90°, because the two p-orbitals are aligned along the x and y axes and are therefore perpendicular.
	wulfenite.fandm.edu /Intro_to_Chem/valence_bond_and_mo_models.htm (844 words)

	Chemical Bonding
		The type of bonding that occurs when a nonmetal accepts an electron from a metal is referred to as ionic bonding and the bond is called an ionic bond.
		In Valence Bond Theory, bonding is viewed as occurring by the overlap of two atomic orbitals, one from each atom.
		Bond strength is defined as the amount of energy needed to homolytically break a bond (each of the nuclei takes one of the two electrons from the bond).
	chemistry.armstrong.edu /P1/Bonding.html (804 words)

	Valence bond theory (via CobWeb/3.1 planetlab2.tamu.edu) (Site not responding. Last check: 2007-11-06)
		For example, what is said to be a sigma bond is the frontal overlapping of atomic orbitals.
		However, the atomic orbitals for bonding may not be "pure" atomic orbitals directly from the solution of the Schrödinger equation.
		Valence bond theory has been extended to Molecular Orbital Theory, which explains this hybridisation as linear combinations of the wavefunctions associated with each atom involved.
	valence-bond-theory.iqnaut.net.cob-web.org:8888 (199 words)

	BBC - h2g2 - Valence Bond Theory of Chemical Bonding.
		The bond is allowed to form by the pairing of the spins of the unpaired electron of the constituent atoms.
		The simplest example is the formation of four bonds to four hydrogen atoms in the methane molecule, CH The energy put in to promote the 2s electron is more than made up by the formation of the two extra C-H bonds than would have been possible otherwise.
		The more accurate and developed theory of chemical bonding that is used in virtually all modern computational work is molecular orbital theory is dealt with in part II.
	www.bbc.co.uk /dna/hub/A986556 (3101 words)

	Molecular Orbital Theory
		Molecular orbital theory is more powerful than valence-bond theory because the orbitals reflect the geometry of the molecule to which they are applied.
		Bond orders can be calculated from Lewis structures, which are the heart of the valence-bond model.
		In molecular orbital theory, we calculate bond orders by assuming that two electrons in a bonding molecular orbital contribute one net bond and that two electrons in an antibonding molecular orbital cancel the effect of one bond.
	chemed.chem.purdue.edu /genchem/topicreview/bp/ch8/mo.html (1304 words)

	Duran: Chapter Twelve Molecular Orbital Theory (Site not responding. Last check: 2007-11-06)
		They are the VSEPR Theory (with Lewis Dot Structures), the Valence Bond Theory (with hybridization) and Molecular Orbital Theory.
		Unlike the V-B theory, which treats the electrons as localized baloons of electron density, the MO theory says that the electrons are delocalized.
		The answer is dilithium because it has a bond order of 1 which is stable and diberylium has a BO of 0 which is unstable and therefore will not form.
	www.chem.ufl.edu /~chm2040/Notes/Chapter_12/theory.html (706 words)

	Valence Bond Theory (Site not responding. Last check: 2007-11-06)
		The Valence Bond approach to electronic structure theory in indisputably the "natural" theory for describing bond formation and chemical processes.
		This theory is called the Valence Bond Self Consistent Field (VB-SCF) method and incorporates into VB theory the advances made in molecular orbital theory.
		Qualitative valence bond theory is immensely useful in constructing models of electronic structure for use in discussing the break-up of molecules after they have been irradiated with light.
	www.chm.bris.ac.uk /pt/dynamics/vb.htm (733 words)

	Valence BonD THEORY
		Two theories have evolved from quantum mechanics which assist the chemists in describing the experimental observations in terms of the atomic or molecular orbitals in a compound.
		The strength of the bond depends on the amount of overlap; the greater the overlap of the orbitals the stronger the bond.
		Another conflict with the Valence Bond Model is found with ammonia, NH Here is a QuickTime movie of the chemical bond in NH The movie shows the electron configuration for a nitrogen atom and for the hydrogen atoms.
	intro.chem.okstate.edu /1314F97/Chapter9/Wed123971.html (1154 words)

	Re: Whats up with the Lewis dot structure of sulfate?
		Overlap of the remaining one-electron orbitals results in a double bond, with one lone pair of electrons on carbon and two on oxygen; all this is shown schematically in Figure 4.
		Of course, valence-bond theory requires that we mix these two models (which can in fact be stated mathematically); this is called "resonance" and is represented schematically in Figure 5.
		bonds are "interchanged" by resonance, and the net result is similar to that shown in the resonating Lewis structures of Figure 12.
	www.madsci.org /posts/archives/jan2000/949098457.Ch.r.html (1495 words)

	CHEMystery: Atomic Structure and Bonding: Valence Bond Theory (Site not responding. Last check: 2007-11-06)
		The valence bond theory (VB theory) or the molecular orbital theory (MO theory) explains why and how electrons are shared between atoms.
		The VB theory imagines individual atoms, each with its own orbitals and electrons coming together and forming covalent bonds of the molecule.
		A bond between two atoms is formed when a pair of electrons is shared by two overlapping orbitals, according to the VB theory.
	library.advanced.org /3659/structures/vbt.html (165 words)

	Chemical bond - Wikipedia, the free encyclopedia
		A chemical bond is the physical phenomenon of chemical species being held together by attraction to each other through sharing, as well as exchanging, of electrons and is a phenomenon that is fully described by the laws of quantum electrodynamics.
		There are weaker chemical bonds which are classically explained to be effects of polarity between molecules which contain strong polar bonds, including interactions which result from induced polarity (such as London forces) between the electron clouds.
		Although certain classifications of bonds may generally be classified as "strong" (covalent, ionic), or "weak" (hydrogen, van der waals), care should be taken because the strongest of the "weak" cases can be much stronger than the weakest of the "strong" bonds.
	en.wikipedia.org /wiki/Chemical_bonding (2662 words)

	The Valence-Bond Approach to Bonding in Complexes
		The idea that atoms form covalent bonds by sharing pairs of electrons was first proposed by G. Lewis in 1902.
		The Heitler-London model of covalent bonds was the basis of the valence-bond theory.
		The last major step in the evolution of this theory was the suggestion by Linus Pauling that atomic orbitals mix to form hybrid orbitals, such as the sp, sp
	chemed.chem.purdue.edu /genchem/topicreview/bp/ch12/valence.php (355 words)

	Valence Bond Theory and Hybrid Atomic Orbitals
		The valence bond (VB) approach is different from the molecular orbital (MO) theory.
		However, the atomic orbitals for bonding may not be "pure" atomic orbitals directly from the solution of the Schrodinger Equation.
		A chemical bond is due to the overlap of atomic orbitals.
	www.science.uwaterloo.ca /~cchieh/cact/c120/hybrid.html (2318 words)

	Valence Bond Theory and Hybridization (Site not responding. Last check: 2007-11-06)
		The bonding electrons in such bonds are localized in the region between the two atoms.
		A single bond is composed of two bonding electrons, so the total number of electrons in the two overlapping atomic orbitals used to produce a bond cannot exceed two.
		A bond in which a lone pair is converted into a covalent bond is called a coordinate covalent bond.
	www.pearsoncustom.com /wertz/a_cd/cams/html/c06_structure/s05_vb.html (180 words)

	Chemistry : Chapter 7 : Valence Bond Theory (Site not responding. Last check: 2007-11-06)
		The valence bond theory emphasizes that all the orbitals in bonding are the same.
		For resonance structures, if an atom has a double bond in any of the resonance structures, the hybridization of that atom is determined from the structure when that atom has a double bond.
		hybridization, since the hybridization is determined by the resonance structure with the double bond, where the oxygen has a double bond and two lone pairs.
	www.wwnorton.com /chemistry/concepts/chapter7/ch7_2.htm (314 words)

	Atomic Orbital Theory (Site not responding. Last check: 2007-11-06)
		The basic premise of this theory is that bonds are formed when atoms get close enough so that atomic orbitals on the individual atoms will be able to overlap so that the three dimensional probability regions share a common volume.
		Pi bonds are considerably weaker than any sigma bond which accounts for the fact that Pi bonds are the first to be broken during a chemical reaction.
		This theory is specially designed for carbon chemistry, but it wouldn't be as powerful as it is were it not for the fact that most other atoms can undergo hybridization.
	members.aol.com /profchm/vb.html (2003 words)

	Chemical Bonding
		In the molecular orbital approach, the basic premise is that when atoms get close enough to bond, their atomic orbitals reshape themselves and become a set of molecular orbitals that no longer belong to any one atom but are orbitals for the entire molecular domain.
		Such molecular orbitals are called "bonding molecular orbitals" and are the first orbitals occupied by the available electrons within the molecule.
		Describes covalent bonds in terms of molecular orbitals.
	jgor123.tripod.com /motheory.html (287 words)

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