Chem 1011 – Intersession 2011
Class #16
25-May-11
1
Class 16: Midterm #1 Review
• Section 18.2 – Oxidation Reduction Reactions
• Chapter 9 – Lewis Theory
• Chapter 10 – VSEPR Theory and Valence Bond
Theory
• Chapter 11 – Liquids, Solids and
Intermolecular Forces
• Chapter 12 – Solutions
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Redox Reactions
• Rules for Assigning Oxidation Numbers
• Identifying oxidation, reduction, oxidizing
agents and reducing agents
• Using the half reaction method of balancing
▫ Acidic Solution
▫ Basic Solution
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Lewis Theory
• What is Lewis Theory?
• Arrangement of electrons in Lewis Structures
▫ Covalent Bonds (Bonding Pairs)
 Single, Double and Triple Bonds
▫ Lone Pairs
• The Octet Rule
Review for Midterm #1
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Chem 1011 – Intersession 2011
Class #16
25-May-11
4
Lewis Theory
• Electronegativity
▫ General trend based on periodic table placement
• Bond Polarity
▫ Non-Polar, Polar, Ionic
 Depends on ∆EN
▫ Drawing Bond Dipoles
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Lewis Structures
• Steps to drawing Lewis Structures for molecules /
polyatomic ions
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Valence e–?
Terminal / Central Atoms?
Make the Skeletal Structure with single bonds
Complete the Octets (Terminal Atoms first)
• Is this the best structure?
▫ Assign Formal Charges
• Can I draw this differently?
▫ Check for Resonance
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Lewis Structures
• Where resonance exists, the average of all
structures yields the resonance hybrid
• Will the Octet Rule apply?
▫ Incomplete Octets
▫ Odd-Electron Species
▫ Expanded Octet (3rd row and onwards)
Review for Midterm #1
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Chem 1011 – Intersession 2011
Class #16
25-May-11
7
Bonding in Metals
• Metallic atoms lose their valence electron(s),
which become delocalized
▫ Metal cations are held together by attractions to
the ―electron sea‖
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VSEPR Theory
• What is VSEPR Theory? How does it rationalize
molecular shapes?
• The Five Basic Electronic Shapes
▫ Depend only on the number of electron groups
surrounding the central atom (bonding or lone pairs)
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2 groups – Linear
3 groups – Trigonal Planar
4 groups – Tetrahedral
5 groups – Trigonal Bipyramidal
6 groups – Octahedral
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VSEPR Theory
• What constitutes and electron group?
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Lone Pair
Single (Odd) Electron
Single Bond
Double Bond
Triple Bond
• If all electron groups are bonding, then the
electronic and molecular shape will be the same
Review for Midterm #1
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Chem 1011 – Intersession 2011
Class #16
25-May-11
10
VSEPR Theory
• If some electron groups are lone pairs (or odd
electrons), they will impact molecular shape
▫ Serve as ―placeholders‖ in the electronic geometry.
The atoms take up the remaining positions,
leading to distinct molecular shapes
• Lone pairs provide a stronger repulsive force
than bonding groups
▫ Molecules containing lone pairs generally have
bond angles less than ideal
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Effect of Lone Pairs
• 3 Electron Groups – Trigonal Planar
▫ 3 Bonding, 0 Lone Pairs – Trigonal Planar
▫ 2 Bonding, 1 Lone Pair – Bent
• 4 Electron Groups – Tetrahedral
▫ 4 Bonding, 0 Lone Pairs – Tetrahedral
▫ 3 Bonding, 1 Lone Pair – Trigonal Pyramidal
▫ 2 Bonding, 2 Lone Pairs – Bent
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Effect of Lone Pairs
• 5 Electron Groups – Trigonal Bipyramidal
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5 Bonding, 0 Lone Pairs – Trigonal Bipyramidal
4 Bonding, 1 Lone Pair – See-Saw
3 Bonding, 2 Lone Pair – T-Shaped
2 Bonding, 3 Lone Pairs – Linear
• 6 Electron Groups – Octahedral
▫ 6 Bonding, 0 Lone Pairs – Octahedral
▫ 5 Bonding, 1 Lone Pair – Square Pyramidal
▫ 4 Bonding, 2 Lone Pairs – Square Planar
Review for Midterm #1
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Chem 1011 – Intersession 2011
Class #16
25-May-11
13
VSEPR Theory
• Draw Molecules in 3D using
▫ Straight Lines (in line with the page)
▫ Dashed Wedges (in to the page)
▫ Solid Wedges (out of the page)
• These shapes can be used to describe the geometry
around each central atom in larger molecules
• Determine the Polarity of Molecules based on the sum of
the individual bond dipoles in the molecule
▫ Generally, a perfectly symmetrical molecule made of all the
same bonds will be non-polar
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Valence Bond Theory
• Describe the basic concept of Valence Bond Theory
• Hybridization of Atomic Orbitals
▫ Related to the number of electron groups around the
central atom
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2 Electron Groups = 2 Hybrid Orbitals = sp
3 Electron Groups = 3 Hybrid Orbitals = sp2
4 Electron Groups = 4 Hybrid Orbitals = sp3
5 Electron Groups = 5 Hybrid Orbitals = sp3d
6 Electron Groups = 6 Hybrid Orbitals = sp3d2
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Valence Bond Theory
• Differentiate between sigma (σ) and pi (π) bonds
▫ σ – ―head-to-head‖ overlap of orbitals
▫ Hybrid Orbitals form σ bonds
▫ All Single Bonds are σ, as well the the ―first‖ bond in
double or triple bonds
▫ π – ―side-to-side‖ overlap of orbitals
▫ Valence orbitals remaining after hybridization form π
bonds
▫ After the first bond is formed, all remaining bonds in
double or triple bonds are π
Review for Midterm #1
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Chem 1011 – Intersession 2011
Class #16
25-May-11
16
Solids, Liquids and Gases
• Comparison Table Between each phase
▫ Shape, flow, compressibility, etc.
• Phase Changes
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Solid to Liquid – Melting (Fusion)
Liquid to Solid – Freezing (Solification)
Liquid to Gas – Vaporization (Evaporation)
Gas to Liquid – Condensation
Solid to Gas – Sublimation
Gas to Solid – Deposition
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Intermolecular Forces
• Dispersion Force
▫ Present in all molecules
▫ From a ―temporary‖ dipole based on uneven distribution of
electrons
▫ Dispersion forces increase with:
 Greater number of Total Electrons in the molecule
 If total electrons are equal, the molecule with greater surface
area
• Dipole-Dipole
▫ Present in polar molecules
▫ Based on the attraction of positive to negative ends of
molecular dipoles
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Intermolecular Forces
• Hydrogen Bonding
▫ Very strong dipole force, created by a large
difference in electronegativity
▫ Found in molecules with a hydrogen atom bonded
directly to F, N or O
• Ion-Dipole
▫ Only found in mixtures – not pure molecules
▫ The attraction of an ion to the applicable dipole of
a neighbouring molecule
Review for Midterm #1
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Chem 1011 – Intersession 2011
Class #16
25-May-11
19
Intermolecular Forces
• Within pure molecular samples, IMF’s can be used
to judge boiling / melting points
• Molecules with stronger IMFs will boil at higher
temperatures
• The relative strength of IMFs are (strongest first):
▫ Hydrogen Bonding
▫ Dipole Dipole
▫ Dispersion Forces
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More Phase Changes
• ∆H values for respective changes
• Vaporization of Liquids
▫ Effected by temperature, exposed surface area of the liquid,
strength of IMFs
• Calculating q based on a temperature change or a phase
change
• Vapor Pressure and Boiling Points
▫ Factors affecting both
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Phase Changes
• Phase Diagrams
▫ Describe and Interpret
▫ ―Critical Point‖
• Heating Curve for Water
▫ 5 distinct phases
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Heat Solid Ice
Melt Ice (Convert to Water)
Heat Liquid Water
Boil Water (Convert to Steam)
Heat Gaseous Steam
Review for Midterm #1
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Chem 1011 – Intersession 2011
Class #16
25-May-11
22
Types of Solids
• Molecular Solids
▫ Composed of Individual Molecules
▫ Held together by IMFs
• Ionic Solids
▫ Composed of Cations and Anions
▫ Held together by Ionic Attractions
• Atomic Solids – 3 types
▫ Non-bonding (ie, Noble Gases)
▫ Metallic (all metal elements – ―Sea of Electrons‖)
▫ Network Covalent – all atoms covalently bonded together
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Solutions
• Terminology
▫ Solute, Solvent and Solution
• Types of solutions
▫ Some Phase of Solute dissolved in Some Phase of
Solvent
• Spontaneous Mixing
▫ Spreading out energy to decrease the entropy
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Solutions
• Forming Solutions
▫ Overcoming Intermolecular Forces between
 Solute—Solute
 Solvent—Solvent
▫ And forming new interactions between
 Solute—Solvent
• Will the formation of a solution be favored?
▫ Like Dissolves Like (polar in polar, non-polar in
non-polar)
Review for Midterm #1
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Chem 1011 – Intersession 2011
Class #16
25-May-11
25
Solutions
• Solution Types
▫ Saturated
▫ Undersaturated
▫ Supersaturated
• Describing the make-up of a solution
▫ Molarity
▫ Mole Fraction / Mole Percent
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Solutions
• Colligative Properties
▫ Osmotic Pressure
 π = MRT
• Cellular applications
▫ Hypotonic, Hypertonic and Isotonic
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Good Luck!
• Remember:
▫ No Programmable Calculators!
• The exam begins at 9:00am on Friday in C-4002
• Review Session Thursday at 10:00am in C-3033
• Ask questions! Office or email: [email protected]
▫ Or don’t forget about the Resource Room!
Review for Midterm #1
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