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	Addition of Water
		Bonds are electrons, so making and breaking bonds will change the location of electrons.
		As we study more addition reactions of unsaturated functional groups during the semester, we'll notice that the pi bond in the reactant is typically broken.
		In our instance, the pi bond between carbon and oxygen has disappeared and the hydrogen from water has added to the oxygen while the OH group from water has added to the carbon.
	chemistry2.csudh.edu /rpendarvis/carbaddn.html (1482 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.
		In pi bonds the resulting overlap is not maximum and these bonds are relatively weak.
		bonds, the overlap between C-C atoms is lateral and hence not maximum.
	home.att.net /~cat6a/carb_bonds-I.htm (878 words)

	Pi bond - Information from Reference.com
		Pi bonds are usually weaker than sigma bonds because their (negatively charged) electron density is further from the positive charge of the atomic nucleus, which requires more energy.
		From the perspective of quantum mechanics, this bond weakness is explained by significantly less overlap between the component p-orbitals due to their parallel orientation.
		Although the pi bond by itself is weaker than a sigma bond, pi bonds are most are components of multiple bonds, together with sigma bonds.
	www.reference.com /search?q=Pi%20bond (461 words)

	ChemViz Determination of Pi Bond Strength in the Ethene Molecule Lab (Site not responding. Last check: )
		In this lab the pi bond strength in the ethene molecule is determined by optimizing the carbon-carbon bond length during this transition.
		Rotation of one carbon atom of the double bond in the ethene by ninety degrees breaks the pi bond; this in turn allows a relaxation and a subsequent increase in the bond length during this transition.
		In this lab the bond length of C-C bond is increased, consistent with the loss of the pi bond attraction between the carbon atoms, at 1.34 and 1.46 Ångstrom units.
	chemviz.ncsa.uiuc.edu /content/lab-s-pibond.html (729 words)

	NationMaster - Encyclopedia: Pi bond
		Pi bonds are named after the Greek letter "π", as in p orbitals, since the orbital symmetry of the pi bond is the same as that of the p orbital (when observed down the bond axis).
		Pi bonds are usually weaker than sigma bonds because their orbitals go further from the positive charge of the nucleus, which requires more energy.
		Pi bonds are usually weaker than sigma bonds because their (negatively charged) electron density is further from the positive charge of the atomic nucleus, which requires more energy.
	www.nationmaster.com /encyclopedia/Pi-bond (799 words)

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

	Carbon - MSN Encarta
		A covalent bond is a bond formed when two atoms share a pair of electrons.
		The pi bond does not hold electrons as tightly as the sigma bond holds the first pair.
		That is, pi electrons more easily split away from the bond and create bonds with other atoms, adding those atoms to the molecule.
	encarta.msn.com /encyclopedia_761577017/Carbon.html (1066 words)

	Covalent bond (Site not responding. Last check: )
		Covalent bonding is an intramolecular form of chemical bonding characterized by the sharing of one or more pairs of electrons between two components, producing a mutual attraction that holds the resultant molecule together.
		Pure covalent bonds (which are usually non-soluble, are electrically non-conductive, and tend to exist as individual molecules), and ionic bonds (which are soluble, are electrically conductive when molten or in solution, and, in general, tend to exist in a crystalline form) are on two opposite ends of the spectrum and have different properties.
		Bond order is a term that describes the number of pairs of electrons shared between atoms forming a covalent bond.
	www.dejavu.org /cgi-bin/get.cgi?ver=93&url=http://articles.gourt.com/%22http%3A%2F%2Farticles.gourt.com%2F%3Farticle%3Dcovalent (1251 words)

	IB Chemistry higher level notes: Hybridisation
		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)
		Bond measurements show us that this is not the case - this can be explained by the concept of resonance.
	ibchem.com /IB/ibnotes/full/bon_htm/14.2.htm (2040 words)

	Valence bond theory-Molecular orbital theory-Theories Of Chemical Bonding-Sigma bond-Pi bond-Formation of sigma ...
		Sigma bonds are the strong bonds due to maximum overlapping of orbitals.
		The relative strength of a sigma bond is related to the extent of overlap of the atomic orbitals.
		A Pi bond is formed by the lateral or side ways or parallel overlapping of P-orbital of the atoms which are already bonded by a sigma bond and their axes are coplanar.
	www.citycollegiate.com /bond_theoryXIa.htm (492 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)

	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)

	Pi bond - Information from Reference.com
		Pi bonds result from parallel orbital overlap: the two combined orbitals...
		Pi bonds involve the electrons in the leftover p orbital for each carbon atom.
		This is because pi bonds form from the sideways overlap of unhybridized p...
	dictionary.reference.com /search?q=Pi%20bond (320 words)

	Alkene Reactivity
		Remember, the bond energies of a molecule are the energies required to break (homolytically) all the covalent bonds in the molecule.
		When an unsymmetrically substituted double bond is protonated, we expect the more stable carbocation intermediate to be formed faster than the less stable alternative, because the activation energy of the path to the former is the lower of the two possibilities.
		Since initial electrophilic attack on the double bond may occur equally well from either side, it is in the second step (or stage) of the reaction (bonding of the nucleophile) that stereoselectivity may be imposed.
	www.cem.msu.edu /~reusch/VirtualText/addene1.htm (3530 words)

	P and Q
		The cleavage of one or more covalent bonds in a molecular entity resulting from absorption of light, or a photochemical process in which such cleavage is an essential part.
		Polarizability along the bond joining a substituent to the rest of the molecule is seen in certain modern theoretical approaches as a factor influencing chemical reactivity, etc., and parametrization thereof has been proposed.
		Because the pi and sigma atomic orbitals that interchange roles are orthogonal, such a reaction does not proceed through a fully conjugated transition state and is thus not a pericyclic reaction and therefore not governed by the rules that express orbital symmetry restrictions applicable to pericyclic reactions.
	www.chem.qmul.ac.uk /iupac/gtpoc/PQ.html (1935 words)

	30
		hybrid orbitals and a pi bond from the overlap of p
		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.
	www.uoregon.edu /~ch111/L30.htm (740 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)

	How Things Work - Question 618
		Hydrogen atoms can form a single bond to each other, oxygen atoms can form a double bond to each other, and nitrogen atoms can form a triple bond to each other.
		This arrangement is reasonably effective for lowering the energy of the system and is called a "pi bond." The third covalent bond is also a pi bond, but it forms 90° from the first pi bond, as though the two people are now touching their heads and their feet together along with their hands.
		With a sigma bond and the two pi bonds between the atoms, there is no room for additional electrons.
	howthingswork.virginia.edu /page1.php?QNum=618 (497 words)

	SparkNotes: SAT Chemistry: Valence Bond Theory
		Since the pair of electrons is attracted to both atomic nuclei, a bond is formed, and as the extent of overlap increases, the strength of the bond increases.
		The electron density of a sigma bond is greatest along the axis of the bond.
		As we mentioned earlier in this chapter, pi (p) bonds result from the sideways overlap of p orbitals, and pi orbitals are defined by the region above and below an imaginary line connecting the nuclei of the two atoms.
	www.sparknotes.com /testprep/books/sat2/chemistry/chapter4section9.rhtml (633 words)

	Molecular Structure Calculations Answers
		The S-F bonds in the trigonal plane, S1-F3 and S1-F5, are stronger with a bond order of 0.872 than the axial bonds with a bond order of 0.638.
		The hybridization of the P1-O3 bond is sp
		Bonding to a more electronegative atom increases the p character on the less electronegative atom (see Bent's rule and Question 1).
	www.colby.edu /chemistry/webmo/MSCanswers.htm (667 words)

	Aromaticity Detection in Marvin
		Another representation is that of the circular pi bond, in which the electron density is evenly distributed through a pi bond above and below the ring.
		Process: locate the ring atoms in the molecule connected with single and double bonds respectively, sum the number of electrons and if the Hückel's rule is valid, then the ring is aromatic.
		Locate the ring atoms in the molecule connected with single and double bonds respectively, sum the number of electrons and if the Hückel's rule is valid, then the ring is aromatic.
	www.chemaxon.com /marvin/doc/user/aromatization-doc.html (479 words)

	World of Carbon
		A covalent chemical bond is formed between two atoms when their orbitals overlap and share a pair of electrons.
		The interaction of the loosely held electrons, in the pi bonds, with light is responsible for its fl color.
		The bond angles are all 109 degrees, typical of sp3 hybridization.
	invsee.asu.edu /nmodules/Carbonmod/bonding.html (725 words)

	Vision
		In the cis-retinal, the hydrogens (light gray in the molecular model on the left) are on the same side of the double bond (yellow in the molecular model).
		In fact, all of the double bonds are in the trans-configuration in this isomer: the hydrogens, or hydrogen and -CH3, are always on opposite sides of the double bonds (hence, the name "all-trans-retinal").
		This excitation "breaks" the pi component of the double bond and is temporarily converted into a single bond.
	www.elmhurst.edu /~chm/vchembook/533cistrans.html (354 words)

	Introduction to Inorganic Chemistry
		Pi bonding is very common seen in the organic compounds, it has a nodal plane in the center of orbital.
		Delta bond is a new one in the inorganic compound, it is not appear at organic molecules, because it use d-orbitals to produce it.
		So it is a very weak bond than sigma bond and pi bond, it often seen at metal-metal multiple bonding.
	inorganic.chemistry.pu.edu.tw /first/New/B.html (363 words)

	ROCO Resonance: geometry
		And the CN bond in compound IV ("in between" N) is somewhere "in between": 140 pm.
		Any time a N (equipped with a lone pair) lies next to a pi system, it may be possible to delocalize the N lone pair by converting it into a pi bond pair.
		All 6 CC bond distances are identical, and at 140 pm they lie in between the distances observed for normal CC single bonds (153 pm) and double bonds (134 pm).
	academic.reed.edu /chemistry/roco/Resonance/geometry.html (1324 words)

	Hybridization: Page 5
		Pi bonds are used to provide the extra electrons needed to fulfill octet requirements.
		A Sigma bond is a bond formed by the overlap of two hybrid orbitals through areas of maximum electron density.
		A Pi bond is a bond formed by the overlap of two unhybridized, parallel p orbitals through areas of low electron density.
	www.bcpl.net /~kdrews/hybridization/hybrids5.html (511 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.
		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.
		Pi bonds are like pointing two fingers at the ceiling and moving them sideways until they touch.
	library.thinkquest.org /C004970/atoms/sigmapi.htm (245 words)

	Spartanburg SC \| GoUpstate.com \| Spartanburg Herald-Journal (Site not responding. Last check: )
		In an ethene monomer, one electron pair is held securely between the two carbons in a sigma bond.
		The other is more loosely held in a pi bond.
		The free radical uses one electron from the pi bond to form a more stable bond with the carbon atom.
	www.goupstate.com /apps/pbcs.dll/section?category=NEWS&template=wiki&text=radical_polymerization (619 words)

	Polymerization reactions (Site not responding. Last check: )
		The pi bond in this configuration is not as strong as a carbon-carbon sigma bond.
		It is the unpaired electron that "attacks" the carbon carbon double bond, as depicted below, where the free radical is designated with the letter R and the unpaired electron is the dot (a representation consistant with a Lewis dot symbol for such a species).
		The produce bonds that form the polymer - and they produce water molecules that are somehow removed from the reaction mixture in the processing of the reaction.
	www.uwm.edu /~tholme/old105/polymerization.htm (548 words)

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