ppt14 a - web.chem.ucsb.edudevries/chem1c/handouts/ppt14 a.pdf · 4/5/2010 1 covalent...

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Covalent Bonding:Covalent Bonding: Orbitals

The Central Themes of VB Theory

Basic Principle

•A covalent bond forms when the orbitals of two atoms overlap and are occupied by a pair of electrons that have the highest probability of being located between the

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the highest probability of being located between the nuclei.

Themes

•These overlapping orbitals can have up to two electrons that must have opposite spins (Pauli principle).

•The valence orbitals in a molecule are different from those in isolated atoms.

Figure 12.18: Three representations of the hydrogen 1s


Figure 13.1: (a) The interaction of two hydrogen atoms (b) Energy profile as a function of the distance

between the nuclei of the hydrogen atoms.


Figure 13.1: (a) The interaction of two hydrogen atoms (b) Energy profile as a function of the distance

between the nuclei of the hydrogen atoms.


Figure 12.19b: Representation of the 2p orbitals.


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Hydrogen, H2

3 WAYS TO FORM σMOLECULAR ORBITALS


Hydrogen fluoride, HF

Fluorine, F2

What about The other 2Atomicp orbitals?

Figure 14.1: (a) Lewis structure of the methane molecule (b) the tetrahedral molecular geometry

of the methane molecule.


Figure 14.2: valence orbitals on a free carbon atom


Figure 14.1: (a) Lewis structure of the methane molecule (b) the tetrahedral molecular geometry

of the methane molecule.


Figure 14.3: native 2s and three 2p atomic orbitals characteristic of a free carbon atome are combined to

form a new set of four sp3 orbitals.


Carbon 1s22s22p2

Carbon could only make two bondsif no hybridization occurs. However,carbon can make four equivalent bonds.


s

px py pz

sp3

hybrid orbitals

Ene

rgy

sp3

C atom of CH4 orbital diagram

B

A

BB

B

Brown, LeMay, Bursten, Chemistry The Central Science, 2000, page 321

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Figure 14.4: Cross section of an sp3 orbital


The four sp3 hybrid orbitals in CH4

Promotion


Figure 11.9 The bonds in ethane.

both C are sp3 hybridizeds-sp3 overlaps to bonds


sp3-sp3 overlap to form a bondrelatively even

distribution of electron density over all

bonds (Greek sigma) bondshave axial symmetry andgood overlap

Rotation about C-Cbond allowed.

Figure 14.6: Tetrahedral set of four sp3

orbitals on the carbon atom


Figure 14.7: The nitrogen atom in ammonia is sp3 hybridized.



Promotion


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Promotion


The four sp3 hybrid orbitals in NH3

Promotion


N


Promotion


N

Figure 11.5 The sp3 hybrid orbitals in H2O

Lone pairs


Diamond - sp3 hybridized C


Figure 14.8: The hybridization of the s, px, and py atomic orbitals results in the formation of three

sp2 orbitals centered in the xy plane.


NB: The remaining p orbital can be empty or serve another function

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The three sp2 hybrid orbitals in BF3

PromotionNote the single left overUnhybridized p orbital on B


Region of overlap

Unhybridized p orbital on B

Hybrid Orbitals

2s 2p

Ground-state B atom

2s 2p

B atom with one electron “promoted”


s

px py pzEne

rgy

sp2 2p

B atom of BH3 orbital diagram

hybridize

s orbital

p

sp2

hybrid orbitals

p orbitalssp2 hybrid orbitals shown together

(large lobes only)three sps hybrid orbitals

H

H

HB

Figure 14.10: When one s and two p oribitals are mixed to form a set of three sp2 orbitals, one p orbital remains unchanged and

is perpendicular to the plane of the hybrid orbitals.


Figure 14.13: (a) The orbitals used to form the bonds in ethylene. (b) The Lewis structure for ethylene.


The plastics shown here were manufactured with ethylene.


Source: Comstock - Mountainside, NJ

Figure 14.11: The σ bonds in ethylene.


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Figure 14.12: A carbon-carbon double bond consists of a σ bond and a π bond.


Figure 14.48: The benzene molecule consists of a ring of six carbon atoms with one hydrogen atom bound to

each carbon; all atoms are in the same plane.


• Sp2 hybridized

FIGURE 14.49: Sigma BondingSystem in Benzene

FIGURE 14.50: (a) Pi MO System in Benzene, (b) Delocalized Pi MO Over Entire Ring of C

Atoms

N

O

N

O

N

O


N

O O

N

O O

N

O O

FIGURE 14.51: (a) Pi BondingSystem in NO3

-, (b) Delocalized Electronsin the pi MO System of NO3

- Ion

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Graphite – sp2 hybridized C


Fullerene-C60 and Fullerene-C70

What hybridization of C describes the structures?


Figure 14.14: When one s orbital and one p orbital are hybridized, a set of two sporbitals oriented at 180 degrees results.


The sp hybrid orbitals in gaseous BeCl2

Promotion

Promote to create two half filled orbitals that participate in


Why are sp hybrids invoked? Because if Be made one bond with its2s and one bond with a 2p orbital, then the two Be-Cl bonds would have different strengths & lengths. But both bonds are identical.

participate in bond formation

Filled 2s orbital can’t bond to Cl

The two sp hybrid orbitals in gaseous BeCl2


Note the two “leftover” p orbitals of BeRegion of overlap

Figure 14.15: The hybrid orbitals in the CO2 molecule


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Figure 14.16: orbital energy level diagram for the formation of sp hybrid orbitals of carbon.


Figure 14.17: Orbitals of an sp hybridized carbon atom


sp2 hybridization of an oxygen atom

4 atomicorbitals

s p


1 trigonalBond with2 lone pairs+ 1 for a pi bond

sp2 px

4 hybridizedorbitals

sp2 px

Figure 14.18: Orbital arrangement for an sp2

hybridized oxygen atom


Figure 14.19: (a) Orbitals predicted by the LE model to describe (b) The Lewis structure for carbon dioxide


Hybrid Orbitals

Types of Hybrid Orbitals


sp sp2 sp3 sp3d sp3d2

Shapes: linear triangular tetrahedral trig. bipyram. Octahedral# orbitals: 2 3 4 5 6

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Promotion


N



Promotion

Figure 14.20: (a) An sp hybridized nitrogen atom (b) The s bond in the N2 molecule (c) the two p bonds

in N2 are formed


The conceptual steps from molecular formula to the hybrid orbitals used in bonding.

M l l h

Step 1 Step 2 Step 3


Molecular formula

Lewis structure

Molecular shape and e- group arrangement

Hybrid orbitals

sp3 hybridization of a carbon atom

4 atomicorbitals

s p



sp3

4 tetrahedralbonds

sp3



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sp3 hybridization of a nitrogen atom

4 atomicorbitals

s p


3 tetrahedralbonds with1 lone pair sp3


sp3

sp3 hybridization of a nitrogen atom


N

sp3 hybridization of a oxygen atom

4 atomicorbitals

s p


2 tetrahedralbonds with2 lone pairs sp3


sp3

sp3 hybridization of a oxygen atom



4 atomicorbitals

s p


3 trigonalBonds+ 1 for a pi bond sp2 px


sp2 px


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sp2 hybridization of an oxygen atom

4 atomicorbitals

s p


1 trigonalBond with2 lone pairs+ 1 for a pi bond

sp2 px


sp2 px

Figure 14.19: (a) Orbitals predicted by the LE model to describe (b) The Lewis structure for carbon dioxide


sp hybridization of a carbon atom

4 atomicorbitals

s p



sp

2 linearbonds+ 2 for pi bonds sp py

py

px

px

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sp hybridization of an nitrogen atom

4 atomicorbitals

s p



sp

1 linearBonds with1 lone pair+ 2 for pi bonds

sp py

py

px

px

Figure 14.20: (a) An sp hybridized nitrogen atom (b) The s bond in the N2 molecule (c) the two p bonds

in N2 are formed


Figure 14.21: A set of dsp3 hybrid orbitals on a phosphorous atom


Hybridization Involving d Orbitals

3s 3p 3d 3s 3p 3d

promote

hybridizeunhybridized P atom

P = [Ne]3s23p3vacant d orbitals


five sp3d orbitals 3dF

F

FP

F

F

Be

Be

Be

Ba

Ba

Trigonal bipyramidal

hybridize

degenerateorbitals

(all EQUAL)

[ ] p

Figure 11.6 The five sp3d hybrid orbitals in PCl5


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Figure 14.22: The orbitals used to form the bonds in the PCL5 molecule


Figure 14.23: An octahedral set of d2sp3

orbitals on a sulfur atom



Figure 11.7

The six sp3d2 hybrid orbitals in SF6

Figure 14.24: The relationship among the number of effective pairs, their spatial arrangement,

and the hybrid orbital set required


Figure 14.24: The relationship among the number of effective pairs, their spatial arrangement,

and the hybrid orbital set required (cont’d)


Figure 11.8

The conceptual steps from molecular formula to the hybrid orbitals used in bonding.

Molecular formula

Lewis structure

Molecular shape and e- group

t

Hybrid orbitals

Step 1 Step 2 Step 3


formula structure arrangement orbitals

Figure 10.1 Figure 10.12 Table 11.1

ppt14 a - web.chem.ucsb.edudevries/chem1c/handouts/ppt14 a.pdf · 4/5/2010 1 covalent...

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