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Topic: Sigma bond

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	IB Chemistry higher level notes: Hybridisation
		Sigma bonds are produced by any direct orbital overlap along the axis joining the two nuclear centres together.
		When a sigma bond is formed by direct orbital overlap and this brings two parallel 'p' orbitals into close proximity then these can overlap sideways (laterally) to form a region of electron density that is not directly between the two nuclear centres but which nevertheless contributes to bonding.
		In this molecule the bond angles indicate that the shape of the molecule is a perfect tetrahedron with bond angles of 109º 28' (approximately 109,5º)
	ibchem.com /IB/ibnotes/full/bon_htm/14.2.htm (2040 words)

	Pi Bonds
		The pi bond does not overlap in the region directly between the two carbon atoms where the sigma bond is formed.
		A double bond consists of a sigma bond (using hybrid orbitals) and a pi bond (using p orbitals).
		The sigma bonds (or sigma orbitals) are shown as the dark shaded areas in this drawing.
	dl.clackamas.cc.or.us /ch106-02/pibonds.htm (753 words)

	Sigma Bonds (Site not responding. Last check: 2007-10-13)
		molecule, the sigma bond was formed by the overlap of two 1s orbitals.
		The strength of a bond is directly related to the match in energy levels for the two atomic orbitals and in the quality of the overlap.
		Bonding orbitals are called "bonding" because electrons are more stable in such orbitals than in the atomic orbitals that overlapped to form the bonding orbital.
	www.chm.davidson.edu /ChemistryApplets/MolecularOrbitals/overlap/sigma.html (771 words)

	#1 Site For Learning Chemistry
		The C atom is at the center of the tetragon (three dimensional equilateral triangle) and the four H in the four corners of the tetragon.
		Sigma bonds are strong and the electron sharing is maximum.
		In pi bonds the resulting overlap is not maximum and these bonds are relatively weak.
	home.att.net /~cat6a/carb_bonds-I.htm (878 words)

	Sigma Bonds
		This particular kind of covalent bond in which electrons are shared between atoms is called a sigma bond.
		The distinguishing feature of a sigma bond (or sigma bonding orbital) is that the overlap region lies directly between the two nuclei.
		This diagram shows the sigma bond formed by the overlap of hybrid orbitals from two carbon atoms.
	dl.clackamas.cc.or.us /ch106-02/sigma.htm (313 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.
		In the valence bond, atomic orbitals of bonded atoms overlap, and electrons orbit around the atoms and also in the bond region.
		Typically, a sigma bond is the primary bond, and up to two pi bonds may also be made.
	www.iscid.org /encyclopedia/Valence_Bond_Theory (211 words)

	Valence Bond and MO models (Site not responding. Last check: 2007-10-13)
		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.
		This means that a double bond does not have the strength of two single bonds and is also more susceptible to attack by external atoms that are searching for electron density.
	wulfenite.fandm.edu /Intro_to_Chem/valence_bond_and_mo_models.htm (844 words)

	Sigma verse Pi Bonds (Site not responding. Last check: 2007-10-13)
		There is a distinction made between the types of bonds which form as orbitals overlap.
		One way in which these bonds differ is in their location with respect to the internuclear axis (a line which connects the nuclei of two bonded atoms)...
		In a sigma bond, orbital overlap is always along the intermuclear axis so the bond is centered directly between the two nuclei.
	www.brynmawr.edu /Acads/Chem/saved/svpbonds.html (161 words)

	The Net Equation: Your Online Source for Chemistry Solutions
		Sigma bonds occur when s orbitals, p orbitals pointing along the axis to the other bonding atom, or hybridized orbitals collide and overlap; the region of maximum electron density is between the two bonded atoms and lies along the axis between them.
		Sigma bonds are like taking the index finger from each hand and pointing them directly at each other, so one fingertip touches another.
		Pi bonds occur when p orbitals (usually those left over from orbital hybridization) perpendicular to the axis of bonding overlap; in this case, the region of highest electron density is "above" or "sideways from" the axis between bonding atoms.
	library.thinkquest.org /C004970/atoms/sigmapi.htm (245 words)

	CCP4 Program Suite : refmac - Input and output files (Site not responding. Last check: 2007-10-13)
		The B-value of CA Asn50 of chain B deviates from the average B-value by 20.00; the sigma for this B-value is 1.5.
		This means the rigid bond restraint between atoms N of Leu12 chain A and C of Leu12 of chain A deviate from 0 by 4.625, the sigma for the rigid bond restraint in terms of B values is 2.0.
		The first number is the number of covalent bond lengths, the second is the root mean square deviation of the bond lengths from the dictionary values and the third is the average sigma for this restraint type.
	www.ysbl.york.ac.uk /~garib/refmac/docs/files/log.html (4435 words)

	SparkNotes: Conformations of Alkanes: Conformations of Ethane
		The circle in the Newman projection represents the atom in front of the bond, and the lines radiating from the center are the bonds of that atom.
		The bonds of the rear atom emerge from the sides of the circle.
		In the staggered conformation, the C-H bonds on the rear carbon lie between those on the front carbon with dihedral angles of 60 degrees.
	www.sparknotes.com /chemistry/organic2/conformations/section1.html (756 words)

	Functional Groups - Bonding
		This bond is referred to as a sigma bond since it is shaped like a cylinder (hot dog) and the letter sigma is the first letter of the greek word for cylinder.
		The term pi is used because half of this bond extends above the plane of all three sigma bonds and half extends below that plane.
		One bond is a sigma bond, represented by the sausage, and the other is a pi bond, represented by the bun.
	chemistry2.csudh.edu /rpendarvis/funcgr.html (1334 words)

	Valence Bond Thoery
		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.
		For example in ethylene, H2C=CH2, each "C" atom is connected to three sigma bonds, one to each hydrogen and one toe the neighboring C atom, and one "pi" bonding pair between the carbons.
	www.csubak.edu /~mdutton/u8c211.html (757 words)

	electronegativity - polar bonds in organic compounds
		The bonding pair is in the second energy level of both carbon and fluorine, so in the absence of any other effect, the distance of the pair from both nuclei would be the same.
		Because the bonding pair is pulled towards the fluorine end of the bond, that end is left rather more negative than it would otherwise be.
		The polarity of the carbon-halogen bonds is important in the reactions of the halogenoalkanes.
	www.chemguide.co.uk /basicorg/bonding/eneg.html (1067 words)

	30
		As with carbon-carbon double bonds, carbon-carbon triple bonds are not free to rotate, but the concept of cis-trans isomers about a triple bond does not make sense.
		This is not the case, the c-c double bonds are all the same length in benzene.
		The pi-bonding electrons (see a picture of the pi-bonding in benzene) in benzene are said to be delocalized and it is this delocalization that gives benzene and related compounds their low chemical reactivity.
	www.uoregon.edu /~ch111/L30.htm (740 words)

	Chemical Bonding: hybrid orbitals
		Each carbon is bonded to three other atoms in the same kind of plane trigonal configuration that we saw in the case of boron trifluoride, where the same kind of hybridization occurs.
		The triple bond in acetylene is seen to consist of one s bond joining the line-of-centers between the two carbon atoms, and two p bonds whose lobes of electron density are in mutually-perpendicular planes.
		Pi bond delocalization furnishes a means of expressing the structures of other molecules that require more than one electron-dot or structural formula for their accurate representation.
	www.chem1.com /acad/webtext/chembond/cb07.html (3221 words)

	Organometallic HyperTextBook: Sigma Bond Metathesis (Site not responding. Last check: 2007-10-13)
		As shown in the drawing, a sigma-bonded ligand is replaced through reaction with the sigma bond of an incoming ligand.
		Sigma bond metathesis is generally confined to those systems where oxidative addition is not a viable pathway.
		Sigma bond metathesis plays a critical role in certain olefin polymerization reactions and is frequently encountered in reactions involving dihydrogen or silanes.
	www.ilpi.com /organomet/sigmabond.html (208 words)

	bk5
		Point out the C-H bond in the model that should be denoted by a "wedge", and also point out the C-H bond that should be indicated by a "dotted line" if the structure were to be drawn on a piece of paper.
		The type of bond formed from two orbitals with “end-on” overlap is said to be a “sigma bond” “Sigma bonds” make up most of the framework of organic molecules.
		The C-H bond in ethyne is shorter than the C-H bond in ethene, which is shorter than the C-H bond in ethane.
	www.chem.unl.edu /cak/bk5.htm (2001 words)

	Sigma & Zeta Bond
		That is not what the bond was established for, and that is not true in even the closest blood family.
		Sigma and Zeta have been about this common fellowship since Zetas inception in 1920, so of course we have the history and know how to make such a bond work no matter where you go, but as in any relationship it is based on the choices of the involved parties.
		That is why the bond transcends those who are aligned in the ranks of Sigma and Zeta, but it is something that is held dear and sacred by those who PLEDGED their loyalty to our cause.
	www.mtsu.edu /~pbs/zeta.html (734 words)

	Answers for Bonding (Site not responding. Last check: 2007-10-13)
		In an ionic bond an electron is transfered from a metal to a nonmetal to form ions.
		The bond is mostly due to the electrostatic attraction of the oppositely charged ions.
		Any single bond in a structure is a sigma bond formed by the head-to-head overlap of orbitals.
	home.att.net /~v.d.singleton/genchem/bondans.htm (423 words)

	hybrid orbitals
		Both of these facts are difficult to immediately rationalize given the spatial arrangement of the valence orbitals in C (the 2s and the three 2p orbitals), and the fact that the 2s orbital is filled in the ground state of the carbon atom.
		Therefore there are three "pi bonds", but since there is no reason to prefer one form of pi interaction over the other (as is the case with the two resonance structures above) those three pi bonds are delocalized over the whole molecule.
		This "ring" represents three pi bonds, so each CC bond is considered a 1.5 bond since there is a sigma bond and half of a pi bond.
	www.wellesley.edu /Chemistry/chem120/hybrids.html (848 words)

	General Chemistry 115
		A single bond is composed of (a.) a sigma bond (b.) a pi bond (c.) a sigma bond and a pi bond (d.) a sigma bond and two pi bonds (e.) a pi and two sigma bonds.
		A triple bond is composed of (a.) a sigma bond (b.) a pi bond (c.) a sigma bond and a pi bond (d.) a sigma bond and two pi bonds (e.) a pi and two sigma bonds.
		This increase causes the electron density of the O - H bond to decrease as electrons are attracted towards E, thus weakening the O - H bond.
	www.cbu.edu /~mcondren/c115e396.html (446 words)

	CBU CHEM115 Exam3 2002
		A double bond is composed of (a.) a sigma bond (b.) a pi bond (c.) a sigma bond and a pi bond (d.) a sigma bond and two pi bonds (e.) a pi and two sigma bonds.
		A hydrogen bond results when a lone pair of electrons on a very electronegative atom attract a hydrogen atom on another molecule or on another part of the same large molecule.
		This is due to (a.) one is a base and the other an acid, (b.) number of hydrogen bonds each can form or (c.) one is attached to a sugar and the other a phosphate.
	www.cbu.edu /~mcondren/c115e302.htm (754 words)

	Alkenes, Alkynes, and Aromatic Compounds (Site not responding. Last check: 2007-10-13)
		Bonding in alkenes and alkynes: hybridization, sigma bonds, and pi bonds
		A double bond is made up of one sigma bond and one pi bond, a triple bond of one sigma bond and two pi bonds
		First the atomic numbers of the atoms bonding to the double-bonded carbon atoms is examined, and then the atomic numbers of the atoms bonded to those atoms is checked, and so on until a classification is determined
	www.xmission.com /~seldom74/chem1120/ch13/13_index.htm (1825 words)

	Atomic Orbital Theory
		A third type of sigma overlap is the overlap between an "s" orbital and a "p" orbital such as when a Hydrogen atom's "s" orbital overlaps with a "p" orbital of another atom like a Chlorine atom.
		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 would mean that the two sp hybrid atoms have a sigma bond (overlap between the sp orbitals) and two Pi bonds (overlap of the p orbitals) or a total of three bonds.
	members.aol.com /profchm/vb.html (2003 words)

	Answers to Homework Set #1 (Site not responding. Last check: 2007-10-13)
		The carbons bonded to the oxygen are trigonal planar.
		A sigma bond is formed by the overlap (combination) of to atomic orbitals (or hybrid orbitals) in the space directly between the two atoms.
		The pi bond is formed on both sides of the space occupied by the sigma bond.
	www.wsu.edu /~genchem/chem102/notes/hwk01ans.htm (747 words)

	[No title]
		Sigma bonds are the most common bonds in organic chemistry.
		Summary of Hybridization Rule 1: Both sigma bonding electrons and lone pairs occupy hybrid orbitals, so the number of hybrid orbitals is equal to the number of sigma bonds plus the number of lone pairs on the atom.
		Diagram 2-8 The sigma bond is cylindrical, and is unaffected by rotation of one of the CH2 groups.
	crab.rutgers.edu /~alroche/Ch02.doc (1894 words)

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