vs
vs
vs
CSUMB
ESSP 311 Organic Chemistry I
Ronald W. Rinehart, Ph.D.
Chapter 1 Chemical Bonding
| Blackwell's "11th Hour" tutorial on
structure, bonding, and properties http://www.blackwellpublishing.com/11thhour/book6/oc1ch1.html http://www.blackwellpublishing.com/11thhour/book6/index.html > Chapter 1 |
| Dr. Robert Wiley's tutorial on bonding
and isomerism http://www.amug.org/~rwiley/Organic_Chemistry_Site/bonding_and_isomerism.htm |
| Organic Chemistry Online by Paul R.Young
at the University of Illinois at Chicago Structure and Bonding tutorials [requires MDL Chime™; use Netscape™] http://www.chem.uic.edu/web1/OCOL-II/WIN/STRUCT.HTM |
|
From Oxford University, there is a really good tutorial on chemical bonding in
organic molecules, based on Foundations of Chemistry by Richard E.
Dickerson and Irving Geis. [requires MDL Chime™; use Netscape™] go to: http://www.chem.ox.ac.uk/vrchemistry/orbitals/html/page01.htm |
| Carey PowerPoint slides for chapter 1 [1.1 to 1.6, atoms,
orbitals, bonds, polarity, formal charge] from Columbia University can be
seen at http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/01_01_06.html |
| Carey PowerPoint slides for chapter 1 [1.7 to 1.9,
structural formulas, constitutional isomers, resonance] from Columbia
University can be seen at http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/01_07_09.html |
| Carey PowerPoint slides for chapter 1 [1.10 to 1.11,
molecular shapes, molecular dipole moments] from Columbia University can be
seen at http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/01_10_11.html |
| Carey PowerPoint slides for chapter 1 [1.12 to 1.14,
electron waves, bonding, VB and MO models] from Columbia University can be
seen at http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/01_12_14.html |
| Carey PowerPoint slides for chapter 1 [1.15 to 1.19,
hybridization and bonding] from Columbia University can be seen at http://www.columbia.edu/itc/chemistry/c3045/client_edit/ppt/01_15_19.html |
| A set of 154 PowerPoint slides on structure and bonding
in PDF format by Paul R. Young of the University of Illinois at Chicago can be seen at http://www.chem.uic.edu/web1/PDF/CH1.PDF You will need both Adobe Acrobat™ Reader 4.0 and Apple's QuickTime™ to view these presentations |
| Introduction to organic
chemistry [including chemical bonding] by Gary Trammell and Srinivas Vuppuluri at the University of Illinois at Springfield http://people.uis.edu/gtram1/organic/introtoorgchem.htm |
Chapter
1. Chemical Bonding
I. Review of Orbitals and Bonding
A. Orbitals
1. Orbitals represent probability regions of
high electron density about the nucleus.
2. Atomic orbitals can be s, p, d, f.
3. Valence electrons are electrons in the
outermost energy levels.
4. Electrons of an atom can be described in
terms of its electron configuration.
5. Atoms and ions tend to be most stable in a
noble gas configuration (an "octet").
a) Ionization energy.
Na. + energy ----> Na+ +
e-
b) Electron affinity.
Cl + e- ----> Cl¯ +
energy
B. Bonding.
1. Ionic Bonds: Electron
transfer.
a) Metal - Nonmetal
b) Example: NaCl
Na 1s22s22p63s1
Cl 1s22s22p63s23p5
Na+ 1s22s22p6
Cl- 1s22s22p63s23p6
2. Covalent Bonds: Sharing of electrons.
a) Nonmetal - Nonmetal or
Nonmetal - Metalloid
b) Nonpolar Covalent Bonds- Equal (or nearly equal) sharing of
electrons.
The two bonding atoms have equal (or nearly equal)
electronegativities:
less than 0.5 units difference in electronegativity.
c) Polar Covalent Bonds- Unequal
sharing of electrons: greater than 0.5
units difference in electronegativity.
i) Classify the following
bonds:
C-H O-H C-O
Mg-I
d) Dipole moment:
m
= e ∙ d
where e is the charge in
esu (electrostatic units), d is the
distance separated in cm, and
m
is the dipole moment in Debyes.
3. Hybridization
|
see the
Hybrid Orbital Tutorial at Colby College [you need Shockwave™]
|
a) sp3
hybrids: CH4 C2H6
i) 109.5o
bond angles
ii) 25% s
character
iii) sigma bonds
iv) tetrahedral
b) sp2
hybrids: CH2=CH2
i) 120o bond
angles
ii) 33.3% s
character
iii) sigma bonds and pi
bonds
iv) trigonal planar
center
c) sp hybrids:
HC≡CH
i) 180o bond
angles
ii) 50% s
character
iii) sigma bonds and pi
bonds
iv) linear
4. Molecular Orbitals
a) Combinations of atomic orbitals
result in molecular orbitals.
b) In-phase overlap of atomic
orbitals result in bonding molecular orbitals.
c) Out-of-phase overlap of atomic orbitals result in antibonding
molecular orbitals.
d) End-to-end overlap of s,
sp, sp2, sp3 results in sigma
(s)
bonds.
e) Sideways overlap of p-orbitals
results in pi
(p)
bonds.
f) Examples: H2
H2-
He2
O2
O2+
O2-
II. Lewis Structures.
|
See
Colby College's Shockwave tutorial "Representing Compounds"
See the page on
Lewis Structures by Brenda Wojciechowski and Paul Cerpovicz
Lewis Structures by Steven Hardinger at UCLA |
A. Drawing Lewis Structures.
1. Add all valence electrons and divide by 2. This gives the number of
electron pairs for bonding
and nonbonding (lone pairs) purposes.
2. First connect the atoms with single bonds,
then distribute the other pairs as lone
pairs.
3. If some atoms lack an octet try using
multiple bonds.
4. Examples: H2 F2
O2 N2 CH2O H2O
CH4 C2H6
C2H4 C2H2
5. Calculate
formal charges:
FC = Group # - (# unshared electrons +
bonds)
a) Examples: CH3+
CH3¯ CH3∙
H3O+ H2SO3
|
See the page on
formal charge by Brenda Wojciechowski and Paul Cerpovicz at Georgia
Southern University at
See the page on
formal charge by Linda M. Sweeting at Towson State University at
Formal Charge
by Steven Hardinger at UCLA
See my page on common covalent bonding patterns
including the associated formal charges at |
B. Valence Shell Electron Pair Repulsion: VSEPR
|
I have
compiled an extensive list of great websites devoted to atomic orbitals and
VSEPR at
See the page on
VSEPR by Brenda Wojciechowski and Paul Cerpovicz at Georgia Southern
University at |
1. Used to predict the shape of a molecule based upon the number of electron pairs about the central atom.
|
Total Pairs on |
Bonding |
Nonbonding |
Shape |
Example |
Approximate Bond Angle |
|
4 |
4 |
0 |
tetrahedral |
CH4 |
109.5o |
|
4 |
3 |
1 |
trigonal pyramid |
NH3 |
109.5o |
|
4 |
2 |
2 |
angular |
H2O |
109.5o |
|
3 |
3 |
0 |
trigonal planar |
BCl3 |
120o |
|
3 |
2 |
1 |
angular |
NO2— |
120o |
|
2 |
2 |
0 |
linear |
CO2 |
180o |
2. Treat multiple bonds as a single electron
pair about the central atom.
3. Hierarchy of repulsion between electron
pairs (from highest to lowest):
a) lone-pair - lone-pair
b) lone-pair - bonded pair
c) bonded pair - bonded pair
4. Electrons in multiple bonds take up more
space than those in a single bond. For this
reason the bond angle between H-C=O in formaldehyde is greater than 120o
and less
than 120o for
H-C-H.
5. Predict the shape for the following
examples:
CH3:¯
CH2O
CH3+ C2H4
C2H2
H2O2 CO32-
C. Resonance.
|
See the page on
Resonance Structures by Brenda Wojciechowski and Paul Cerpovicz
See the page on
resonance structures by Linda M. Sweeting at Towson State University at
Resonance
practice problems by Jim Puckett at Harvard University
Drawing Resonance
Structures by Steven Hardinger at UCLA |
1. Lewis structures show electrons in specific
localized regions between two nuclei in a
covalent bond or on a single atom as a lone pair.
2. In certain cases more than one Lewis
structure can be drawn for a particular
molecule or polyatomic ion: resonance structures.
3. Pay particular attention to the meaning of:
↔
vs
vs
vs
vs
|
|
|
|
|
|
|
resonance arrow |
reaction arrow |
equilibrium arrows |
curly arrow |
half-curly arrow |
|
Used to join two or more different resonance structures for the same molecule |
Indicates a chemical reaction |
Indicates a reversible chemical reaction |
Indicates origin and movement of a pair of electrons when showing the
mechanism of a reaction. |
Indicates origin and movement of a single electron when showing the
mechanism of a reaction. |
|
See the Curly Arrows tutorial by
Mary Masson at the University of Aberdeen at |
|
Curved Arrows tutorial by Steven Hardinger at
UCLA |
4. Resonance hybrids.
5. Resonance represents a breakdown of the Lewis concept since it
implies a delocalization of electrons.
6. Best structures have:
a) octets for each atom.
b) least formal charge.
c) no adjacent like charges.
d) charge on proper element (with
respect to electronegativity).
7. Examples: SO2 CO32¯
C6H6 OPN CH3CO2¯
D. Molecular Dipole Moments.
|
See
Intermolecular Interactions by Roberta Kleinman at Lockhaven University of
PA at
and Polarity and
Intermolecular Forces by Roberta Kleinman at Lockhaven University of PA at |
1. Compounds with only nonpolar covalent bonds
consist of nonpolar molecules.
2. Compounds with only polar covalent bonds may
consist of either polar or nonpolar
molecules, depending upon the shape of the molecule.
a) Asymmetric molecules (with polar
covalent bonds) have dipole moments:
HCl H2O CH2O
b) Symmetrical molecules (with or
without polar covalent bonds) lack dipole
moments:
CO2 CF4
BCl3
|
For greater
appreciation of the importance of dipolar attractions (and other intermolecular
attractive forces) |
III. Structural Formulas
A. Constitutional Isomers (Structural Isomers).
1. Compounds which share the same molecular
formula but differ in structure, specifically
in their atomic connections.
2. Example: C2H6O
Ethyl Alcohol
Dimethyl Ether
b.p. 78.3 oC
b.p. -24.9 oC
Liquid at RT
Gas at RT
Reacts with Na No
reaction with Na
3. Structure is extremely important since it
determines the chemical and physical
properties of a compound. Other examples:
a) Proteins.
b) Vitamin C.
B. Writing Structural Formulas.
|
See
Colby College's Shockwave tutorial "Representing Compounds"
See Drawing
Organic Molecules by Jim Clark at
The
different ways of depicting organic structures are discussed by Bill
Robinson of Purdue University at
Guide to drawing organic molecules by Joan Cheng at Harvard University
Connectivity: What is attached to what by Roberta W. Kleinman at Lock
Haven University of PA
SODAR: Sum Of Double
Bonds And Rings |
1. Lewis Structure.
2. Condensed Structural Formula. CH3CH2CH2CH2CH3
3. Carbon Skeleton Formula (Bond-line
Formulas).
4. Write condensed structural formulas for the
following compounds expressed in
carbon skeleton formulas:
a)
b)
c) 
d)
Many thanks to Rod Oka of
MPC for generously sharing his "Lecture Companion" outline, reproduced here
by permission with
web references and other goodies added by me.
Structures redrawn using ACD Labs ChemSketch™ and MDL IsisDraw™
updated 9/15/07
