CHEM 121:General Chemistry II

Dr. Wanda Oehrli (Early)

Welcome back!

“All the world is a laboratory to the inquiring mind”

• Martin H. Fischer• (1879 - 1962)• German-American physician and writer

• An education in chemistry and science can be applied to a broad variety of problems.

Today’s Agenda• Roll sheet, please sign and note your TEAM #• Introductions• Start Chapter 11• Syllabus

Grew up in DeKalb

Kalamazoo College & MSU

B.A. Chemistry, 1992 Ph.D. Chemistry, 1997

Ph.D. Research

• Optical Sensors• Funded by the Air Force• Benzene, Toluene, Zylene

(BTEX) are used to clean jet engines

• BTEX leach into ground water

• Bioremediation

NRC Postdoctoral Research FellowCenter for Advanced Research in Biotechnology and

National Cancer Institute

1997-2004Protein FoldingGroEL GroESHow do heat shock proteins work?

Biopharmaceutical Development of drugs for cancer based on antibodies and other biomolecules

Teaching 2005-2008 & Ball Horticultural

KishwaukeeBeloitRock ValleyElmhurstHarper

Flower seed germination

Got Married

2009- Present

MBA – DePaulConsulting Work

Nanotechnology company in S. DakotaGreen Certification Company in CA

Investment Advisor FirmInternet Marketing

Back to teaching

I want to get to know you!

• Please fill out the info sheet as thoroughly as possible

• This information will help me get to know you and shape the course for your needs

Gen. Chem. Lab

• Lab begins next week! January 16!– Lab Safety and Math Review

• No class of January 20 (MLK Week) & no lab that week

• Lab resumes week following week

Office Hours

My office is Parmer 319• M,W, F 10:30 -11:30 (meet in 310 if 319 is

occupied)• Or by appointment (e-mail me)

• Office hours will be posted on the myDU page each week

Reading for Friday January 10:Sections 11.1-11.2

There will be a Reading Quiz at the beginning of class on Friday!

Pre-Class Reading Assignment

Chapter 11Intermolecular Forces

15

A Molecular Comparison of Liquids and Solids

A Molecular Comparison of Liquids and Solids• Converting a gas into a liquid or solid requires

the molecules to get closer to each other:– cool or compress.

• Converting a solid into a liquid or gas requires the molecules to move further apart: – heat or reduce pressure.

• The forces holding solids and liquids together are called intermolecular forces.

Intermolecular Forces

Intermolecular Forces• The covalent bond holding a molecule together is an

intramolecular forces.• The attraction between molecules is an intermolecular force.• Intermolecular forces are much weaker than intramolecular

forces • (e.g. 16 kJ/mol vs. 431 kJ/mol for HCl).• Ex. Less energy is required to vaporize liquid HCl than

to form an HCl bond

• When a substance melts or boils the intermolecular forces are broken (not the covalent bonds). When a substance condenses intermolecular forces are formed.

Intermolecular Forces

There are four types of intermolecular forces (IMF) for covalent molecules:

• London Dispersion Forces (LD)• Dipole-Dipole (D/D)• Hydrogen bonding (H-bond)• Ion-Dipole (I/D, only in water solutions)

We see evidence of these intermolecular forces as they affect the boiling point and melting point of compounds.– As IMF increase … bp and mp increase

• London Dispersion Forces (LD)• Dipole-Dipole (D/D)• Ion-Dipole (I/D, only in water solutions)• Hydrogen bonding (H-bonding)

• First two are called van der Waals

Strength of IM Forces

2-10 kJ/mol

15 kJ/mol

5-25 kJ/mol

Polarity of MoleculesDipole Moments of Polyatomic Molecules

Induced Dipoles or Instantaneous Dipoles

Neutral molecules and atoms can induce a charge in each other

London Dispersion Forces

The fluctuating charge distribution in an atom can give rise to an instantaneous dipole moment.

When two atoms are close, their fluctuating dipole moments are correlated, leading to attraction.

London Dispersion Forces

• These forces are present in all molecules, whether they are polar or nonpolar.

• The tendency of an electron cloud to distort in this way is called polarizability.

Factors Affecting London Forces

• The strength of dispersion forces tends to increase with increased molecular weight.

• Larger atoms have larger electron clouds that are easier to polarize.

Syllabus

• Go over syllabus with your “Team”– Introduce yourselves– Take a few minutes to read the syllabus– Then, with your team, come up with at

least 3 questions you have about the class that are NOT answered on the syllabus

– Write the questions down on a 4 x 6 card (one card per team)

– I will collect the cards when you are done and put together a handout answering the questions.