11

AnnouncementsAnnouncements & Agenda& Agenda (02/07/07)(02/07/07)Exam @ 11 am this Friday (Start = 10:45 am)Exam @ 11 am this Friday (Start = 10:45 am) Review Wed @ 3 pm, Here (SC 1019)Review Wed @ 3 pm, Here (SC 1019) Covers Ch 1-5 +Intermolecular Forces (Notes) + LabCovers Ch 1-5 +Intermolecular Forces (Notes) + Lab WILL NOT include Ch 7 except the notes from todayWILL NOT include Ch 7 except the notes from today

TodayToday Intermolecular Forces (Notes: Will be on Exam)Intermolecular Forces (Notes: Will be on Exam) Exam Procedures Exam Procedures Exam TopicsExam Topics

22

Last Time: Energy of Chemical RxnsLast Time: Energy of Chemical Rxns

• The activation The activation energy is the energy is the minimum energy minimum energy needed for a needed for a reaction to take reaction to take place.place.

• When a collision When a collision provides energy provides energy equal to or equal to or greater than the greater than the activation energy, activation energy, product can form.product can form.

33

Summary of Endo- & Exothermic RxnsSummary of Endo- & Exothermic Rxns

Reaction Reaction Energy Energy Heat Heat TypeType ChangeChange in in

ReactionReaction

Endothermic Heat absorbed Endothermic Heat absorbed ReactantReactant

Exothermic Heat released Exothermic Heat released ProductProduct

44

Summary of Reaction RatesSummary of Reaction Rates

State the effect of each on the rate of reaction as:State the effect of each on the rate of reaction as:1) increases 2) decreases1) increases 2) decreases 3) no change 3) no change

A. increasing the temperature. A. increasing the temperature. 11B. removing some of the reactants. B. removing some of the reactants. 22C. adding a catalyst. C. adding a catalyst. 11D. placing the reaction flask in ice. D. placing the reaction flask in ice. 22E. increasing the concentration of one of the E. increasing the concentration of one of the

reactants. reactants. 11

55

Intermolecular Forces (Notes Only)Intermolecular Forces (Notes Only)

Inter-Inter- vs.vs. Intra-Intra- Latin:Latin: Between Between AmongAmong moleculesmolecules moleculesmolecules

3 types: 3 types:

Dispersion ForcesDispersion ForcesDipolar ForcesDipolar ForcesHydrogen BondingHydrogen Bonding

66

Melting & Boiling PointsMelting & Boiling PointsBoth are indicators of the strengths of Both are indicators of the strengths of intermolecular forces:intermolecular forces:

freezing pointfreezing point (fp): the temperature at which a solid & (fp): the temperature at which a solid & liquid coexist at equilibrium under ‘normal’ pressuresliquid coexist at equilibrium under ‘normal’ pressures

boiling pointboiling point (bp): the temperature at which a liquid & (bp): the temperature at which a liquid & vapor coexist at equilibrium under ‘normal’ pressuresvapor coexist at equilibrium under ‘normal’ pressures

Exam Questions: Exam Questions:

(a)(a)Rank Compounds by BPs OR Rank Compounds by BPs OR

(b)(b)Explain why one compound has a higher bp/mp Explain why one compound has a higher bp/mp than another based on IM forces ORthan another based on IM forces OR

(c)(c)Be able to make a sketch showing interactions Be able to make a sketch showing interactions between two moleculesbetween two molecules

77

Intermolecular forces: Intermolecular forces: Actually all the same force!Actually all the same force!

ElectrostaticElectrostatic

Dispersion Forces: Dispersion Forces: From polarizability of atomsFrom polarizability of atoms

Dipolar Forces: Dipolar Forces: From permanent dipole momentsFrom permanent dipole moments

Hydrogen-bonding:Hydrogen-bonding: Special case of dipolar forcesSpecial case of dipolar forces

88

… … but remember that intermolecular but remember that intermolecular forces are weaker than covalent or ionic forces are weaker than covalent or ionic

bonds!!!!bonds!!!!

99

1. Dispersion Forces1. Dispersion Forces

Found in all molecular substancesFound in all molecular substances

Arise from attractions involving Arise from attractions involving induced dipoles.induced dipoles.

Magnitude depends on how easy it is to Magnitude depends on how easy it is to polarizepolarize the the electron cloud of a molecule.electron cloud of a molecule.

larger molecules have larger larger molecules have larger polarizabilitypolarizability..

Ask me about Ask me about Geckos?Geckos?

1010

Polarizability increases…. with increasing MM

p. 92

1111

1. Dispersion Forces:1. Dispersion Forces: Larger shapes are more polarizableLarger shapes are more polarizable

Higher boiling point

1212

Intermolecular ForcesIntermolecular Forces

Intermolecular forces not only hold small molecules in liquids and solids together, but also drive very large molecules to bind to each other - this is necessary for cell functions.

(Turn on a gene)

1313

Individually, dispersion (van der Waal’s) forces are thought of as very weak. However, these forces between large molecules can be very strong - e.g. motor oil, vaseline are entirely non-polar molecules.

In water “hydrophobic bonding” drives large non-polar molecules or parts of molecules together.

Sodium dodecyl sulfate (= sodium lauryl sulfate)

CH3-CH2 -CH2 -CH2 -CH2 -CH2 -CH2 -CH2 -CH2 -CH2 -CH2 -CH2-SO3-

Nonpolar Hydrophobic = “water-hating” Ionic

Hydrophillic = “water loving”

1. More on London Dispersion Forces1. More on London Dispersion Forces

1414

2.2. Dipolar ForcesDipolar Forces

Occur when one polar molecule encounters Occur when one polar molecule encounters another polar molecule.another polar molecule.The positive ends will be attracted to the The positive ends will be attracted to the negative ends.negative ends.Dipolar forces are typically Dipolar forces are typically strongerstronger than than dispersion forces.dispersion forces.Dipolar forces increase with an increase in the Dipolar forces increase with an increase in the polarity of the molecule.polarity of the molecule.NOTE: Ion-dipole forces stronger than dipolar NOTE: Ion-dipole forces stronger than dipolar forces.forces.

1515

2. Dipolar Forces: 2. Dipolar Forces: permanent dipole monents….permanent dipole monents….

Higher boiling point

1616

ExampleExampleExplain the trend in bp’s: butane (0°C), methyl ethyl Explain the trend in bp’s: butane (0°C), methyl ethyl ether (8°C) and acetone (56°C).ether (8°C) and acetone (56°C).

1717

• Special case of dipole-dipole forces.• By experiments: boiling points of compounds with

H-F, H-O, and H-N bonds are abnormally high.• Intermolecular forces are abnormally strong.

3. Hydrogen Bonding3. Hydrogen Bonding

1818

Hydrogen BondingHydrogen Bonding

1919

Hydrogen Bonding

Hydrogen BondingHydrogen Bonding

2020

-

+

Electron deficient H atom

Electronegative atom with lone pair

p. 94

2121

Exam Procedure (GOOD LUCK!!!)Exam Procedure (GOOD LUCK!!!)

When you arrive, leave ALL belongings to the side of the When you arrive, leave ALL belongings to the side of the room except pencils and a calculatorroom except pencils and a calculatorSit ONLY where an exam has been placedSit ONLY where an exam has been placedAcademic integrity is expectedAcademic integrity is expectedSome things you CANNOT do: Some things you CANNOT do: You CANNOT use the programming functions on calculatorsYou CANNOT use the programming functions on calculators You CANNOT temporarily loan your calculator to a neighborYou CANNOT temporarily loan your calculator to a neighbor You CANNOT use a cell phone or any other interactive deviceYou CANNOT use a cell phone or any other interactive device

Do not begin the exam until instructed to do so (10:45)Do not begin the exam until instructed to do so (10:45)To be fair to everyone, you must turn in your exam when To be fair to everyone, you must turn in your exam when instructed (11:50)instructed (11:50)I will provide a Periodic TableI will provide a Periodic Table

2222

Big-Picture Exam TopicsBig-Picture Exam TopicsCh 1 & 2 (~20-30 %)Ch 1 & 2 (~20-30 %)

Units, Sig. Figs., Prefixes, Problem SolvingUnits, Sig. Figs., Prefixes, Problem Solving Type of Energy, Energy in Nutrition, Specific Heat, Type of Energy, Energy in Nutrition, Specific Heat,

Heating/Cooling Curves (States of Matter)Heating/Cooling Curves (States of Matter)

Ch 3 (~20-30 %)Ch 3 (~20-30 %) Atomic Structure, Elemental Identity, Isotopes, Radioactivity, Atomic Structure, Elemental Identity, Isotopes, Radioactivity,

Periodic Table & Trends, Electron Energy LevelsPeriodic Table & Trends, Electron Energy Levels

Ch 4 (~20-30 %)Ch 4 (~20-30 %) Octet Rule, Ionic & Covalent Compounds and Naming, Lewis Octet Rule, Ionic & Covalent Compounds and Naming, Lewis

Dots, Bond Polarity (EN), Molecular Shapes & PolarityDots, Bond Polarity (EN), Molecular Shapes & Polarity

Ch 5 & IM Forces (~20-30 %)Ch 5 & IM Forces (~20-30 %) Balancing, Mass Conservation, Redox Reactions, Using the Balancing, Mass Conservation, Redox Reactions, Using the

Mole, Energy in Chemical ReactionsMole, Energy in Chemical Reactions Dispersion, Dipolar, and Hydrogen-bonding IM forces, Ranking Dispersion, Dipolar, and Hydrogen-bonding IM forces, Ranking

based on BP, Sketching Interactions, Compatibility of IM forcesbased on BP, Sketching Interactions, Compatibility of IM forces

MC (10-15%), Short Ans. (~70%), Problem Solving (15-20%) MC (10-15%), Short Ans. (~70%), Problem Solving (15-20%)