Orbital HybridizationEdward A. Mottel

Department of Chemistry

Rose-Hulman Institute of Technology

04/19/23

Atomic Orbitals & Covalent Bonding

Atomic orbitals are mathematical descriptionsof the probable locations of electrons around

an atom.

s, px, py, pz, dxy, dxz, dyz, dx2-y2, dz2, ...

Atomic orbitals can be “blended” togetherto form new orbitals called hybrid orbitals.

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sp Orbital Hybridization

Be

Be

Be

Be

BeThe shape is determined

by the linear combinationsof atomic orbitals

2s + 2pzand 2s - 2pz

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C+

sp2 Orbital Hybridization

C

2s

C+ =

2pz2px sp2

The 2s, 2px and 2pz atomic orbitalsof each carbon are used.

The angle between the orbitals is 120°.

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sp3 Orbital Hybridization

+

2s

+

2pz2px

+ zy

x

2py

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sp3 Orbital Hybridization

four sp3 orbitals

The angle between the orbitals is 109.5°.

Why isn’t the angle 90°?

tetrahedral shape

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Groupsof

ElectronsHybridization

IdealBondAngle

2 sp 180º

3 sp2 120º

4 sp3 109.5º

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Predict the bond angles and the hybridizationof the central atoms

in each of the following structures.

Be••H •• H H

HN

C O

HN••••

• •• •O ••

O ••••

••

O

••

••••

••

H

C N ••••••••••••

• •• •CH

H

H

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Be••H •• H H

HN

C O

HN••••

• •• •O ••

O ••••

••

O

••

••••

••

H

sp3 O

sp2 N

sp3 N

sp C

sp2 C

C N ••••••••••••

• •• •CH

H

H

sp3 C

Predict the bond angles and the hybridizationof the central atoms

in each of the following structures.sp Be

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Beryllium sp Hybridization

Be

Be

Be Beand

Two orbitalseach can hold two electrons

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sp Hybridization

Be

px, py

sp

ener

gy

2s

2p

ao hao

Maximum angle thattwo orbitals can be

apart is 180°.

atomicorbtials

hybrid atomicorbtials

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z

y

x

sp Hybridized BerylliumValence Orbitals

Open orbital contains no electronsLined orbital contains one electronFilled in orbital contains two electrons

The other p-orbitalsof beryllium (px, py)remain unchanged

Be

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sp Hybridized BerylliumValence Orbitals

Open orbital contains no electronsLined orbital contains one electronFilled in orbital contains two electrons

The other p-orbitalsof beryllium (px, py)remain unchanged

HH Be H two sigmabonds

BeH H

Why is it a linear molecule?

H

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Sketch the hybrid atomic orbitals and fill orshade-in the lobes for each indicated atom

H

HN

C O

HN••••

• •• •O ••

O ••••

••

O

••

••••

••

H

sp2 Osp3 O

sp2 N

sp3 N

sp Csp N

sp2 C

C N ••••••••••••

• •• •CH

H

H

sp3 C

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Sketch the hybrid atomic orbitals and fill orshade-in the lobes for each indicated atom

sp2 Osp3 O

sp2 N

sp3 N

sp C sp N

sp2 C

sp3 C

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Ethene

C••••H

••

H••

CH

• •

H • •

Also called ethylene Polymerizes to form polyethylene Each carbon forms three sp2 hybrid orbitals.

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ener

gy

2s

2p

ao

sp2 Hybridization

hao

sp2

The unhybridized py orbital isperpendicular to the sp2 orbitals.

2py

This hybrid setcan hold six electrons.

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Ethene

Top down view(xz plane)

Edge on view

y

To allow for overlap of the unhybridized py orbitals, the bonding in this molecule requires that ethene is planar. All six atoms lie in the same plane.

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Ethene

CCHH

HH

carbon-carbon sigma bonddue to sp2-sp2 overlap

carbon-carbon pi bonddue to 2py- 2py overlap

carbon-hydrogensigma bonds

due to sp2-s overlap

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Methane

C

• •• •

••••H H

H

H

The 2s, 2px , 2py and 2pz atomic orbitalsof carbon are used.

What would be the name of a hybrid orbitalmade from these orbitals?

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sp3 Hybridization

sp3

ener

gy

2s

2p

carbonao

hao

All four hybridatomic orbitalshave the sameenergy.

These four orbitals areenergetically degenerate.

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Methane

HCH

H

Hcarbon-hydrogen

sigma bondsdue to sp3-s overlap

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Ammonia

••N

• •• •

••H H

H

The 2s, 2px , 2py and 2pz atomic orbitals of nitrogenare used

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sp3 Hybridization

sp3

nitrogenao

hao

ener

gy

2s

2p

By hybridizing itsatomic orbitalsnitrogen gains

more stable(lower energy)

orbitals for bonding.

Which of the electrons in thesehybrid atomic orbitals are available for bonding?

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Ammonia

HNH

H

• •

a completely filled inorbital containstwo electrons

nitrogen-hydrogensigma bonds

due to sp3-s overlap

Because of this bonding,the H-N-H bond angle

is close to 109.5° (actually 107°).

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The Structure of Ammonia

What bond angle would be expected if thelone pair of electrons didn't affect the structure?

What bond angle would be expected if theatomic orbitals of nitrogen did not hybridize?

Why is the actual bond angle not exactly 109.5°?

Draw the orbital overlap diagram for the reactionof ammonia and a hydrogen ion.

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Hydrogen Cyanide

CH N

C NH ••••••••••

2 groups of electrons around carbon

sp hybridization H-C-N = 180°

What does the orbitaloverlap diagram look like?

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Hydrogen CyanideC NH ••••••••••

carbonsp hybridized

How many electronsare in each orbital?

nitrogensp hybridized

How many electronsare in each orbital?

hydrogen1s orbital

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Hydrogen CyanideC NH ••••••••••

sigma bondspx orbitaloverlap

py orbitaloverlap

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Hydrogen Cyanide

sigma bonds(between hydrogen and carbon

and carbon and nitrogen)

2 pi bonds

C NH ••••••••••

(between carbonand nitrogen)

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Nitrite Ion

N••••

• •• •O O• •

• •••••

••

N OO

3 groups of electrons around nitrogen

sp2 hybridization O-N-O @ 120°

Why is the bond angleapproximately 120°?

Draw the hybridizedatomic orbitalsfor each atom

O1 sp2 hybridizedO2 sp3 hybridized

Nitrite IonN••••

• •• •O O• •

• •

••••

••

1s2 2s2 2p4 1s2 2s2 2p3 1s2 2s2 2p4

_ _ _ _ _sp2 p1s

_ _ _ _ _sp2 p1s

_ _ _ _ _sp31s

-1 charge

Nitrite IonN••••

• •• •O O• •

• •

••••

••

What other kind of bond is formed?

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Nitrite IonN••••

• •• •O O• •

• •••••

••

Where is the pi bond located?

O ON

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Nitrite Ion

N OO

How would the bonding changeif O2 was unhybridized?

N••••

• •• •O O• •

• •••••

•• 3 groups of electrons around nitrogen

sp2 hybridization O-N-O @ 120°

Nitrite IonN••••

• •• •O O• •

• •

••••

••

1s2 2s2 2p41s2 2s2 2p4

_ _ _ _ _sp2 p1s

1s2 2s2 2p3

_ _ _ _ _sp2 p1s

-1 charge

_ _ _ _ _2p1s 2s

Nitrite IonN••••

• •• •O O• •

• •

••••

••

What other kind of bond is formed?

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Nitrite IonN••••

• •• •O O• •

• •••••

••

pi bond formation

How could resonance in this molecule be explained?

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EtheneH

HC C

H

H

C••••H••

H••

CH

• •H • •

3 groups of electrons around carbon

sp2 hybridization C-C-H @ 120° H-C-H @ 120°

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EtheneC••••

H

••

H••

CH

• •H • •

How many sigma bonds andhow many pi bonds are formed?

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Ethane

C

H

H

H

C

H

H

H

••C

• •• •

••H

H

H••C

•••• ••H

H

H4 groups of electrons around carbon

sp3 hybridization

C-C-H @ 109.5° H-C-H @ 109.5°

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Ethane••C

• •• •

••H

H

H••C

•••• ••H

H

H

What kind of bonds are formed?

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Dipole Moments

Charge is not always equally distributed in a molecule.

There can be a region of positive charge and of negative charge.

The vector connecting these regions is called the dipole moment.

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Predictions

For molecular compounds• solubility and miscibility are related to the

polarity (i.e., dipole moment) of the molecule.

"Like dissolves like" is a rule of thumb for solubility• polar molecules dissolve in polar solvents

• nonpolar molecules dissolve in nonpolar solvents

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Carbonate Ion

O C

O

O

2-The concept of dipole momentscan also be applied to ions,although they generallydissolve in polar solvents(e.g., water) becauseof their charge.

Although carbonate ionhas no net dipole moment,

it dissolves in polar solventsbecause of its ionic charge.

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Like Dissolves Like

The rule "like dissolves like" is not perfect; However, it does serve as a starting point in

determining what type of solvent to use when attempting to dissolve a solid.

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Polarity Predictions

Rank the following molecules in terms of polarity:• water, benzene, chloroform

O

••

H

• •

H ClClC

H

Cl

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Electronegativity

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