04/19/23

One Point Quiz

One quiz per table, list everyone’s name Agree on an answer You have two minutes

Exam 3 Results

0

2

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50-59%

60-69%

70-79%

80-89%

90-100%

Exam 1 Exam 2 Exam 3

Nomenclature

Average = 95/110

Hardest Questions?

Why is the first ionization energy of nitrogen greater than carbon, oxygen or phosphorous?

Li Be B C N O F Ne124 215 191 260 335 314 402 497 kcal

Primary reason:Change of nuclear charge.

Secondary reason:Electronic configuration effects.

Hardest Questions?

Why is the melting point of magnesium oxide 2000 degrees greater than potassium bromide? (two factors)

Ionic bonding lattice energy q1 x q2 / r

Orbital HybridizationEdward A. Mottel

Department of Chemistry

Rose-Hulman Institute of Technology

04/19/23

Bonding Theories

Ionic Model Skeleton Diagrams Lewis Dot Diagrams Molecular Orbital Theory Orbital Hybridization

• Extends molecular orbitals concepts to atoms

04/19/23

Beryllium Hydride

Be: 1s2 2s2 2p0

H: 1s1Be••H •• H

Impossible to fulfill the octet ofberyllium because there are onlyfour valence electrons available.

Draw a Lewis Dot structure for BeH2

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Beryllium Hydride

Be

BeH

2zb

2sb

HUsing molecular orbitalbonding theory thep-orbitals of berylliummust be used.

This would indicatethat each hydrogen isbound to beryllium bya different type of bond.

Experimentally, the two Be-H

bonds are identicalsame length,

same bond energy (strength)

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Beryllium Hydride

BeH

2zb

2sb

Be H

It is unlikely that2s

b and 2zb

would be exactlyequivalent.

And, there’s another problem ...

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2sb)3

2zb)1

Beryllium Hydride

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

What’s a solution?

HBe

H Be

Be H 2zb)2

H Be 2sb)2

One overlap hasone electron

One overlap hasthree electrons

hybridization

Each overlap hastwo electrons

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Hybridization

The 2s and the 2p orbitals of beryllium have become equivalent to each other by merging or blending or "hybridizing".

These two new orbitals are called sp hybrid atomic orbitals (hao)• Arises from one s orbital and one p orbital.

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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°.

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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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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

HH Be z

y

x

H two sigmabonds

BeH H

Why is it a linear molecule?

H

04/19/23

Ethene

C••••H

••

H••

CH

• •

H • •

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

04/19/23

One Point Quiz

One quiz per table, list everyone’s name Agree on an answer You have two minutes

04/19/23

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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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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Predicting Hybridization

The number of hybrid orbitals an atom formsequals the number of unique directions

that the electron pairs point,as determined by the Lewis Dot structure.

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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 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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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?

04/19/23

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°).

04/19/23

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.

Groups of ElectronsEdward A. Mottel

Department of Chemistry

Rose-Hulman Institute of Technology

Groups of Electrons

H

HN

C O

H

Predicts

bond angles

hybridization ofnon-metal atomsin a molecule or ion

Requires

properly drawnLewis Dot

diagram

04/19/23

Procedure

Draw the proper Lewis Dot diagram. Determine the number of "groups of

electrons" (“effective electron pairs”) around the central atom.• All electrons pointing in the same direction

are considered one group. If only s and p orbitals are involved then the

• correct hybridization and• ideal bond angle is predicted by the number of groups.

04/19/23

Groupsof

ElectronsHybridization

IdealBondAngle

2 sp 180º

3 sp2 120º

4 sp3 109.5º

Groups of ElectronsFormamide

H

HN

C O

H

bond angle

hybridization

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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)

04/19/23

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?

04/19/23

Nitrite IonN••••

• •• •O O• •

• •••••

••

pi bond formation

How could resonance in this molecule be explained?

04/19/23

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°

04/19/23

EtheneC••••

H

••

H••

CH

• •H • •

How many sigma bonds andhow many pi bonds are formed?

04/19/23

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°

04/19/23

Ethane••C

• •• •

••H

H

H••C

•••• ••H

H

H

What kind of bonds are formed?

Dipole MomentsEdward A. Mottel

Department of Chemistry

Rose-Hulman Institute of Technology

04/19/23

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.

04/19/23

Dipole Moment

H Cl••

• •• •

Chlorine is more electronegative than hydrogen.

The dipole moment is drawnpositive (+) to negative(-)

(note: physics texts draw it the opposite way!)

04/19/23

O

••

H

• •

H

Net Dipole Moment

The (net) molecular dipole momentis the vector sum of the individual bond dipoles.

04/19/23

F BF

FBF

F

F

Canceling Dipole Moments

the net dipolemoment of

boron trifluorideis zero

Sometimes a set ofindividual bondmoments canceleach other.

04/19/23

Boron Trifluoride

F BF

F

What is thehybridizationof boron in

borontrifluoride?

Can an alternate Lewis Dot diagram be drawn that obeys the octet rule?

04/19/23

Boron Trifluoride

B••••

• •• •F

F ••••

•• ••

F

••

••••

••

B••••

• •• •F

F ••••

••••

F

••

••••

••

B••••

• •• •F

F ••••

••

F ••••

••••••

What would be the hybridization andbond angles of the resonance structures?

sp2, F-B-F = 120°

04/19/23

H

CH

HH

Canceling Dipole Moments

the hydrogen atomsin methane arearranged in a

tetrahedral shape

the four vectorscancel

each other

The cancellation ofindividual bond momentscan also occurin three dimensions.

04/19/23

Carbon Monoxide

C O•• •••• ••••

negative formalcharge

moreelectronegative

Which way does the dipole ofcarbon monoxide point?

Electronegativity and formal chargeboth contribute to the dipole moment.

04/19/23

Carbon Monoxide

The actual dipole is very small 0.11 D, and points in the direction of carbon!• A debye is 3.336 x 10-30 C·m

C O•• •••• ••••O

••

H

• •

H The dipole moment of thewater molecule is 1.87 D.

04/19/23

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

04/19/23

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.

04/19/23

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.

04/19/23

Polarity Predictions

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

O

••

H

• •

H ClClC

H

Cl

04/19/23

Polarity Predictions

[Cu(py)2(SCN)2] dissolves in chloroform but not water.• Rationalize this behavior.

04/19/23

Electronegativity

04/19/23

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Exam 3 Results

0

1

2

3

4

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6

<60 60-69 70-79 80-89 90-100

Exam 1 Exam 2 Exam3

Nomenclature

Average 89/110 ± 10

Hardest Question?

Rank the following in order of decreasing melting point: CaS, MgO, KCl

Ionic bonding lattice energy q1 x q2 / r2