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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

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Chem 433 9 15 11

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?

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*

DISP

D-D

H-B

Ion-D*

DISP

D-D

H-B

DISP*

DISP

D-D

H-B*

DISP*


CO2

CCl4


Structural Considerations: Bond Radii

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

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-)

B

A

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


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