CHEM 433 - 9/15/11

I. Introductory Topics

C. Intermolecular Forces (handout, 18.1.-18.5)

Conceptual overview cont.

—> Recognizing IMF

Quantitative Considerations

- Energy Scales

- Functional forms

-Structural Considerations

- Adding the repulsive Part

Read: Start Chapter 1 of Atkins

HW #2 via e-mail.. Today or tomorrow AM

Three key questions for identifying IMF?

1) Are ions present?

2) Are polar molecules present?

3) Are there molecules with OH, NH, or FH bonds?

DISPD-DH-B*

DISP* Ion-D*DISPD-DH-B

DISP*

Identify i) all and ii) the most significant IMF in the following liquids or mixtures?

CH3OH (l), C6H6 (l), O2(aq), KBr(aq), Kr(l)

D-ID*DISPD-DH-B

CO2

CCl4

Structural Considerations: Bond Radii

1) http://en.wikipedia.org/wiki/Covalent_radius

2) http://en.wikipedia.org/wiki/Van_der_Waals_radius

http://periodictable.com/Properties/A/VanDerWaalsRadius.v.html

Rvdw (Ar) =

A 2-minute H-Bonding Case Study: “HF Dimer”or (HF)2

R(HF) = 0.919 Å

• E(H-Bond) = 3.6 kcal/mol(15.1 kJ/mol)

• R(H…F) = 1.834 Å(non bond R is ~ 2.7 Å !!!)

• Donor Bond lengthens:R(HF, “A”) = 0.924 Å

• Charge rearrangement:- more polarity - partial e- transfer (0.05 e-)

AB

Data are from a quantum chemical computation… (MP4/aug-cc-pVTZ)