Molecular Orbital Theory 2 -...

Chemistry 201 � Final Exam 1

(C) Pavel SedachLearnfaster.ca

Questions? Suggestions? E-mail me and I will try to find time to reply. [email protected]

All the best!

� Lecture Slides� Booklet Solutions� Test Solutions� Extra notes and advice� Advice on which exams and questions to write� Corrections

Available December 15th at:http://learnfaster.ca/blog/chem-201-final/

Friday, April 14

11:00 to 12:30 Molecular Orbital Theory

12:30 to 13:00 Break

13:00 to 14:15 Functional Groups through VSEPR

14:15 to 14:30 Break

14:30 to 16:00 Hybridization and VSEPR

Saturday, April 15

11:00 to 12:30 Intermolecular Forces in Detail

12:30 to 13:00 Break

13:00 to 14:15 Isomers and Review

14:15 to 14:30 Break

14:30 to 16:00 Review

Molecular Orbital Theory 2

(C) Pavel Sedach Learnfaster.ca

Hybridization vs. Molecular Orbitals(VSEPR)

MO Theory � �� 3


Ener

gy

1s

2s

F F

2p

1s

2s

2p

Linear Combination of Atomic Orbitals (LCAO) is simply Molecular Orbital Theory for two atoms

��



*we assume here that our bond forms along the x-axis

��

�

B.O.=

Ener

gy

2s

F F

2p

2s

2p

��

��

��

��

��

��

�

��



*we assume here that our bond forms along the x-axis

��

��

ABMO

Anti-Bonding Molecular Orbital

Ener

gy

2s

F F

2s

��

�� BMOBonding Molecular Orbital

NBMONon-Bonding Molecular Orbital

2s 2s

2s 2s

MOs of �� 6


�-bonding interaction

�-bonding interactionEner

gy

F F

2p

��

��

��

��

�

2p



F F

Ener

gy

2s

2p

2s

2p

FF



F F

Ener

gy

2s

2p

2s

2p

FF

MO Theory � �� along z-axis 9


VSEPR Predicts

O O

MO Theory Predicts

O O

Ener

gy

2s

2p

2s

2p

OO

MO Theory �� along y-axis 10


2s

2p

2s

2p

ON

VSEPR Predicts

N O

MO Theory Predicts

N O

Ener

gy

MO Theory � �� along y-axis 11


2s

2p

2s

2p

OF

VSEPR Predicts

F O

MO Theory Predicts

F O

Ener

gy

MO Exceptions � Homonuclear Diatomics �� and smaller � along x-axis 12


VSEPR Predicts

MO Theory Predicts

All exceptions:

��

Literally every homonucelardiatomic smaller and including ��.

2s

2p

2s

2p

NN

N N

Ener

gy

MO Theory � Does �� exist? 13


VSEPR Predicts

MO Theory Predicts

All exceptions:

��

Literally every homonucelardiatomic smaller and including ��.

2s

2p

2s

2p

BB

B B

Ener

gy

VSEPR or Valence Bond Theory


14

Intramolecular Bonding 15


The type of bond a compound forms is based on electronegativityElectronegativity is a measure of how much an atom attracts electrons in the bond in molecule

Ionic BondingCovalent Bonding0 1.7 3.4

��

homonucleardiatomics

electron sharing electron transfer

� ��

dipole moment

� � � �

��

�� Covalent

0.5

VSEPRSummary

16

© Pavel SedachLearnfaster.ca

�� / ��

E Shape: linearM Shape: linear

�� / ��

�� / ��

E Shape: trigonal planarM Shape: trigonal planar

E Shape: trigonal planarM Shape: bent, < 120°

�� / ��

�� / ��

E Shape: tetrahedral or TdM Shape: tetrahedral or Td

E Shape: tetrahedral or TdM Shape: trigonal pyramidal

�� / ��

E Shape: tetrahedral or TdM Shape: bent, < 109.5°

�� / ��

E: trigonal bipyramidalM: trigonal bipyramidal

�� / ��

E: trigonal bipyramidalM: see-saw

�� / ��

E: trigonal bipyramidalM: T-shaped

�� / ��

E: Octahedral (Oh)M: Octahedral (Oh)

�� / ��

E: Octahedral (Oh)M: Square Pyramidal

�� / ��

E: Octahedral (Oh)M: Square Planar

�� / ��

E: trigonal bipyramidalM: linear

��

��

��

��

��

Systematic Lewis Structures 17


Step 1 � Count the total number of valence electrons in the structureStep 2 � Arrange the peripheral atoms around the central atom/structure and single bond themStep 3 � Place remaining electrons around peripheral atoms. Place any extra electrons around the central atom.Step 4 � Calculate the formal charges and minimize it by preparing resonance structures

Formal Charge = Valence electrons � lone pair electrons � bonds

Incomplete Valence: �� Expanded Valence: ��

Systematic Lewis Structures 18


Step 1 � Count the total number of valence electrons in the structureStep 2 � Arrange the peripheral atoms around the central atom/structure and single bond themStep 3 � Place remaining electrons around peripheral atoms. Place any extra electrons around the central atom.Step 4 � Calculate the formal charges and minimize it by preparing resonance structures

Formal Charge = Valence electrons � lone pair electrons � bonds

Expanded Valence: ��

Understanding Line Diagrams 19


C has 4 bonds, N has 3 bonds, O has 2 bonds.

To save time drawing structures, we form line diagrams

Because C behaves so reproducibly and forms 4 bonds, we can use line diagrams to represent organic structures. Every vertex(intersection of 2 or more lines) is a carbon atom and it is assumed that C forms 4 bonds

Functional Groups 20Priority Group

1Carboxylic Acids

2Esters

3Amides

4Aldehydes

5Ketones

6 Alcohols

7Amines

8 Ethers

9Alkenes

10 Alkynes

11 Alkyl Halides

12 Alkanes ��

What functional groups are in the following compound?Are there lone pairs missing?Draw a condensed diagram (e.g. where there is a carbon and hydrogen, write CH)


Drawing Proper Tetrahedral Shapes 21


There are VERY few ways to draw a proper tetrahedral structure. Fundamental structures are circled above in the same color.

For organic structures, we typically put a straight chain and just have wedge/hash poking out to one side:

All of these drawings represent EXACTLY the same molecule viewed from different angles

What is wrong with the structures below?

Drawing Proper Trigonal Planar Shapes: 22


Name the functional group, name the structure and draw 3 different VSEPR diagrams:

Resonance, Bond Order and Average Charge 23


Identify the major, minor and intermediate resonance contributors:

��

Does the above compound have an effective resonance hybrid?



Identify the major, minor and intermediate resonance contributors:

��

Does the above compound have an effective resonance hybrid?



��



��

Organic Compounds and Valence Bond Theory


27

Organic Structures � Adding Missing Bonds and Electron Pairs 28


Single, Double and Triple Bonds 29


Bond Strength and Bond Dissociation Energy (Bond Energy)

Bond Length

Single Bond Double Bond Triple Bond

< <

> >Arrange the following bonds according to their bond order (high to low)

i

iiC-N bond

iii, N-O bond

Arrange them again, this time from long to short length

Single Bond Double Bond Triple Bond

Orbital Hybridization (Valence Bond Theory) 30


Count the number of things attached, count the number of orbitals used!

s

p

d

s

p

s

p

s

p

+

Energy diagrams for hybridized atoms 31


Energy diagram ofUnhybridized C

Unhybridized N

Unhybridized O

2s

2p

2s

2p

2s

2p

� bonds are made from sp orbitals� bonds are made from p orbitals � they are any bond above a sigma bond

= __ �, __ � = __ �, __ � = __ �, __ � = __ �, __ �

How many pi bonds are there in the following molecule?

� and � Bonding Frameworks � aka. Valence Bond Theory 32


Valence bond theory is an extension of VSEPR. The two are distinct from MO theory.

� Bonding Framework � Bonding Framework

X

X

X

X

x-axis




X X




y y

VSEPR Structure Hybridization Electronic Shape Molecular Shape Bond Angles Notes

�� linear linear 180�

�� trigonal planar trigonal planar 120�

�� trigonal planar bent, < 120� < 120� Always has a net dipole

�� tetrahedral or Td tetrahedral or Td 109.5�

�� tetrahedral or Td trigonal pyramidal < 109.5� Always has a net dipole

�� tetrahedral or Td bent, < 109.5� < 109.5� Always has a net dipole

�� trigonal bipyramidal

trigonal bipyramidal 120�, 90� *180� is also a possible angle if looking axial to axial


see-saw 120�, 90�, 180� Always has a net dipole. 180� is axial to axial. Equator has more room so lone pairs go there (120� > 90� so more room at equator)


t-shaped 90�, 180� Always has a net dipole. 180� is axial to axial


linear 180� 180� is axial to axial

�� octahedral or Oh octahedral or Oh or square bipyramidal

90�

�� octahedral or Oh square pyramidal 90�, < 90� Always has a net dipole

�� octahedral or Oh square planar 90�

�� unlikely �� octahedral or Oh t-shaped < 90� Always has a net dipole. Never experimentally observed.

�� unlikely �� octahedral or Oh bent, < 90� < 90� Always has a net dipole. Never experimentally observed.

35© Pavel Sedach Learnfaster.ca

Does the molecule have resonance? 36


Resonance is movement of electrons through � bonds

Show possible Resonance Structures for the following compounds 37


IsomersGood place to take a break for Day 1


38

ISOMERS39

Look for a carbon atom with 4 different groups

Not Isomers

IsomersDo the compounds have the same molecular formula?

ConstitutionalStereoisomers

Can the compounds be interconverted by rotation about single bonds?

Conformational Configurational

Is the isomerism at a double bond?

Geometric

YESNO

YES NO

Are the atoms connected the same way?

YES NO

YES NO

Optical

Constitutional

Conformational

Geometric

Optical

Same formula (��), different skeleton!

E-but-2-en-1-olZ-but-2-en-1-ol


Rotate around single bond

Isomers

trans-but-2-en-1-ol

Not Isomers

Isomers

Do the compounds have the same

molecular formula?

Constitutional

StereoisomersCan the compounds be interconverted

by rotation about single bonds?

Conformational

Configurational


GeometricOptical

YES

NO

YES

NO

Are the atoms connected the

same way?

YES

NO

YESNO

e.g. ��vs. ��

��

cis-but-2-en-1-olLook for a carbon atom with4 different groups attached

Constitutional Isomers of �� 41


Draw a molecule that is a ketone, name it:

Draw a molecule that is an aldehyde, name it:

Draw a molecule that is an ether:

Draw a molecule that is an alcohol, name it:

Newman Projections and Conformational Isomers (conformers) of Ethane

© Pavel Sedach Learnfaster.ca

42

Eclipsed

�

� �

Ener

gy

�

� �

�

� �Staggered

Eclipsed

Staggered

�

�

�

�

� �

�

�

�

Isomers

trans-but-2-en-1-ol

Not Isomers

Isomers

Do the compounds have the same

molecular formula?

Constitutional

StereoisomersCan the compounds be interconverted

by rotation about single bonds?

Conformational

Configurational


GeometricOptical

YES

NO

YES

NO

Are the atoms connected the

same way?

YES

NO

YESNO

e.g. ��vs. ��

��

cis-but-2-en-1-olLook for a carbon atom with4 different groups attached

Configurational Isomers - Optical Isomers 44


4 different groups bonded to one atom (usually Carbon)

Is the following molecule chiral? (optically active)? If so, draw its optical isomer.

Configurational Isomers � Geometric Isomers 45


cis/trans

longest carbon chain

E/Zlargest atom (Cahn Ingold Prelog Rules)

Which molecule is the most stable? Why? 46


Does the following compound have a geometric isomer?

Does the following compound have a conformational isomer? A geometric isomer?

Intermolecular ForcesGood place to take a break for Day 1


47

Functional Groups 48(C) Pavel Sedach Learnfaster.ca

Name the functional group. Draw any missing lone pairs. Name the compound.Give the shape around each atom AND state whether it is drawn correctly according to VSEPR:

correct? correct? correct? correct?



correct? correct? correct? correct?



correct? correct? correct?

Basic Intermolecular Forces 51


London Dispersion Forces (Van Der Waals Forces) Dipole-Dipole Bonding

�� - GAS

�� - LIQUID

�� - SOLID

Compound � State at 25° C

Basic Intermolecular Forces 52


Hydrogen Bonding � occurs in the FON elements (HF, OH, NH)

The relative strength of London Dispersion (temporary dipole) forces to Dipole Forces to Hydrogen Bonding isLDF : DD : HB of 1:10:1000

Effects of Intermolecular Forces on Boiling Point 53


Arrange the following from high to low boiling point

Review 54


Methyl ethyl ether is a gas at room temperature (boiling point = 8°C), but 1-propanol is a liquid (boiling point = 97°C). This

difference can be explained mostly by:

a) Covalent bonding

b) London Dispersion forces

c) Dipole-dipole interactions

d) Hydrogen bonding

Review 55


Which of the following has the highest boiling point at 1 atm?

��

��

��

��

Review 56


Rank the following compounds on the basis of decreasing boiling point:

��

��

��

��

��

��

��

��

The ability to stack and London dispersion forces: 57


There is a relationship between some of the compounds below. What is the relationship and which compounds share it?

Arrange all of the above compounds in order of boiling point (high to low)

Expanded Intermolecular Forces for Mixed Solutions 58


Interaction Factors of Interaction

(London dispersion forces)Induced dipole-induced dipole

Polarizability

Dipole-induced dipole

Dipole moment of polar molecule and polarizability of nonpolar molecule.

Dipole�dipole

Dipole moment

Ion-induced dipole

Ion and a compound that has LDF only

Ion-dipole

Ion charge, magnitude of dipole

Hydrogen bonding

Molecule contains H-F or O-H or N-HCan hydrogen bond to secondary molecule that has F, O or N with a free lone pair and no Hs

Intermolecular Forces 59


name



name



Can apply to materials � e.g. hydrophilic vs. hydrophobic 62


hydrophilic

Reactions 63


Show the reaction of lithium hydroxide with ethanoic acid

Show the reaction of ammonia with boron trifluoride

Reactions 64


Show the reaction of triethylamine with butanoic acid

Show the reaction of sodium oxide with water

Cumulative Review


65

Electronic Configurations and Quantum Numbers 66


p

n

+

e-n=1

n=2

n=3

n=4n=5

n=�

Zinc

Cadmium

Arsenic

Copper

*What are all the exceptions to electron filling?

Vanadium (V): ��

OR [Ar] ��

Ge:

Ti:

As ��

Zn:

Ag:

The Valence Electrons are the highest n-value and highest energy orbitals, including the d-orbitals ONLY if they are unfilled!

Put a square around core electrons and circle the valence electrons 67(C) Pavel Sedach Learnfaster.ca

s orbitals

p orbitals

d orbitals

Electronic Configurations 68


Which element is depicted in the diagram below?

Energy

n = 1

n = 2

n = 3

n = 4

n = 5

1s

2s

3s

4s

5s

2p

3d

3p

n = �

Aufbau Principle (Low to High Energy)Hund�s Rule (Single before Pairing)Pauli Exclusion Principle

Diamagnetic? Paramagnetic?

Draw the Electronic Configuration for Co 69


Is cobalt paramagnetic or diamagnetic?

Energy

n = 1

n = 2

n = 3

n = 4

n = 5

1s

2s

3s

4s

5s

2p

3d

3p

Quantum Numbers 70

(C) Pavel Sedach learnfaster.ca

Symbol Possible values

Principal Quantum Number �� (Shell/Energy Level) � ��

Angular Momentum QN (�) (Subshell or Orbital Shape) � ��

Magnetic QN (��) (Specific Orbital in Subshell) ��

Electron spin (��) (Orientation of e- whether up or down) ��

� � ��

��

��

SHAPE

SIZE

ORIENTATION

Electronic Configurations 71


What are the quantum numbers of the circled electrons?

Energy

n = 1

n = 2

n = 3

n = 4

n = 5

1s

2s

3s

4s

5s

2p

3d

3p

n = �

What atom can this possibly be?

Periodic Properties 72


��

Atomic Radius

��

Ato

mic R

adiu

s

Effective Nuclear Charge �� 73


Effective nuclear charge = # protons - # core electrons.

It�s essentially an estimate of the number of protons pulling that electron in towards the atom.If an electron feels a higher effective nuclear charge, it is HARDER to remove.

�� Increases left to right across the periodic table. Due to the way �� is calculated in Chem 201, we don�t see a decrease going down a Group but we should. �� for the d-block is generally not discussed but even unfilled d acts as core ��.

B C N O

Protons 5 6 7 8

Core Electrons 2 2 2 2

�� 3 4 5 6

��

Ionization Energy is the energy needed to remove an e- from an atom (endothermic) 74


Explain why the ionization energy of Mg is greater than Al?

F is greater than O?

Ne is greater than F?

Why does period 3 have a greater ionization energy than period 4?

+475

+675

+875

+1075

+1275

+1475

+1675

+1875

+2075

1 2 3 4 5 6 7 8

1st

Ion

izat

ion

En

ergy

(kJ

/mo

l)

Column/Group (not including the d-block)

Period 2

Period 3

Ionization energy (kJ/mol) is ALWAYS endothermic (it always takes energy to remove electrons from an atom!)

Equation for Ionization: � � ��

Successive Ionization Energies of Carbon 75


The second ionization energy for an atom is always greater than the first. Why?

Where is there an enormous jump in ionization energy and why?

Ionization energy Enthalpy��

��Beginning Shorthand

ConfigurationEquation Final Shorthand

Configuration

1st 1087[He]

� � �� [He]

2nd 2353[He]

�� [He]

3rd 4621[He]

�� [He]

4th 6223 ��

5th 37831 ��

Electron Affinity - Magnitude of how exothermic the absorption of an electron is. 76


Why does Nitrogen have a lower electron affinity than Oxygen?

What process is described by the enthalpy of attachment of the second electron of Aluminum?

Electron Affinity (kJ/mol)

Review 77


What is the �� of the Group 1 elements and the Group 2 elements?

Why is the ionization energy of the Group 15 elements higher than that of the Group 16 elements?

Why is the ionization energy of N bigger than Sulfur?

N, +1402

P, +1012As, +947

O, +1314

S, +1000

Se, +941+925

+1050

+1175

+1300

+1425

2 3 4

1st

Ion

izat

ion

En

ergy

(kJ

/mo

l)

Period/Row (n=2,3,4)

Group 15

Group 16

Large Radii

Atomic Radius is the distance from the nucleus to the outermost electrons. 78

Atomic radius decreases from left to right and across the periodic table.Atomic Radius increases from top to bottom of the periodic table.

Increasin

g Size

Increasing Size

Small Radii


Ionic Radius

Cations are ALWAYS smaller than their neutral atomsAnions are ALWAYS larger than their neutral atoms

Loses Electron

Gains Electron

Anion

��

Cation Neutral

Review 79


1. What are the four periodic trends and how do they vary on the periodic table?

2. What are the exceptions to some trends and why do they occur?

3. Rank the following in order of ionic radius:

��

Orbital Diagrams of the 2s 80

© Pavel Sedachlearnfaster.ca

+r

��

�

��

-r

BOUNDARY DIAGRAMs(also known as LOBE DIAGRAMs)

RADIAL PROBABILITY DIAGRAM

ELECTRON DENSITY DIAGRAM(also known as SCATTER or DOT DIAGRAMs)

r

��

RADIAL PROBABILITY DIAGRAM(typical view)

�spherical� or �radial� node

subshell 1s 2s 3s 2p 3p 3d

� 1 2 3 2 3 3

� 0 0 0 1 1 2

spherical nodes

0 1 2 0 1 0

Radial Probability

Diagram

Scatter Dot Diagram

The following shows the shapes of the radial distribution functions of the atomic orbitals 81


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Molecular Orbital Theory 2 -...

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