Chapa 9 VSEPR b.ppt

7/27/2019 Chapa 9 VSEPR b.ppt

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molecular geometry the orientation of atoms inspace (how the atoms are

arranged in a molecule)

VSEPR TheoryValence Shell Electron PairRepulsion theory

VSEPR is a simple, yet powerful technique to

predict the molecular geometry of molecules

e- pairs (bonding or nonbonding) repel each

other. Thus, they attempt to get as far apart from

each other as possible to maximize separation


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# e- pairs around

central element shapegeometry

name angles

2 pairs linear 180

3 pairstrigonalplanar

120

4 pairs tetrahedral 109.5


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electron pair geometry must be known before

molecular geometry can be predicted

To determine molecular geometry (MG)

1. draw the correct Lewis structure

2. determine # of electron pairs around thecentral element

3. determine how those electron pairs orient

4. attach terminal atoms5. the orientation of the atoms in space

determine the molecular geometry


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determine the molecular geometry of BCl3

MG = trigonal planar


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determine the molecular geometryof BCl2

- (anion)

MG = bent

bent = 3 atoms that are NOT linear


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determine the molecular geometry of H2O

MG = bent


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determine the molecular geometry of NH3

MG = pyramidal


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determine the molecular geometry of CH4

MG = tetrahedral


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tetrahedral pyramidal bent


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multiple bonds in VSEPR theory

* treat a double or triple bond as if it were asingle bond from a VSEPR standpoint

determine the molecular geometry of CO2

MG = linear


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determine the molecular geometry of NO2- (anion)

MG = bent


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Cl2

nonpolar bondelectrons are shared equally in

the bond

polar bondelectrons are NOT shared equally

HCl


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+ -

dipole moment quantitative extent to whichpolarity is measured

Br-Cl has a polar bond


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Is Br-Cl a polar molecule ?

Consider the covalent bond as a rope with

each atom pulling electrons to itself based

on electronegativities of each atom

If the entire molecule moves during the

tugOwar.. the molecule is POLAR

If the entire molecule does NOT move during the

tugOwar.. the molecule is NONPOLAR

Br-Cl is a polarmolecule


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Is CO2 a polar or nonpolar molecule ?

the individual dipoles cancel such

that the overall dipole moment = 0

CO2 is a nonpolarmolecule


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Is H2O a polar or nonpolar molecule ?

MG = bent

H2O is a polarmolecule


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Is NF3 a polar or nonpolar molecule ?

MG = pyramidal

NF3 is a polarmolecule


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Is BF3 a polar or nonpolar molecule ?

MG = trigonal planarthe individual dipoles cancel

such that the overall dipole

moment = 0

BF3 is a nonpolarmolecule


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Is CCl4 a polar or nonpolar molecule ?

the individual dipoles cancel such thatthe overall dipole moment = 0

CCl4 is a nonpolarmolecule

MG = tetrahedral


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valence bond theory describes how atomic

(VB theory) orbitals form bonds

valence bond theory describes how atomic


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open valency unpaired electron in a valenceorbital available for bonding

valence bond theory describes how atomic(VB theory) orbitals form bonds


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F F

2p 2p


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electron promotion electron is removed fromone orbital and placed in

an orbital of higher energy

hybridization simple atomic orbitals on thecentral atom mix to form newhybrid orbitals

hybrid something of a mixed origin


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the two new sp hybrid

orbitals are 50% s-character

and 50% p-character


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Remember, this process is occurring only on

the central element of boron, B

Determine the hybridization of boron, B in BF3


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the 3 new sp2 hybrid orbitals

are 33.3% s-character and

66.6% p-character


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Remember, this process is occurring only on

the central element of carbon, C

Determine the hybridization of carbon, C in CH4


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the 4 new sp3 hybrid orbitals

are 25% s-character and

75% p-character


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octet expansion requires the central atom to

have empty d-orbitals


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sigma bond electron overlap that forms all

single bonds

pi bond electron overlap that forms alldouble and triple bonds

H H

one bondone bond andone bond

one bond andtwo bonds


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three bonds andtwo bondsfive bonds and

one

bond

seven bonds andone

bond


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Chapa 9 VSEPR b.ppt