To Do… Electronic homework (Lon-Capa) HW8 Type 1: due Wed., April 30 by 7 pm Exam 3 review: due...

To Do… Electronic homework (Lon-Capa)

HW8 Type 1: due Wed., April 30 by 7 pm Exam 3 review: due Wed., April 30 by 7pm

Review Sessions Tuesday: 161 Noyes Lab; 6:00-7:50 pm Wednesday: 161 Noyes Lab; 8:00-9:20 pm

Exam #3: Thursday, May 1, 7 pm 114 David Kinley Hall

Intermolecular Forces (IMFs)

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London Dispersion Forces

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London dispersion forces• All molecules exhibit these forces.• Due to temporary and induced dipoles.

• Strongest IMFs for non-polar molecules

• Examples include nitrogen (N2) and methane (CH4).

• With more electrons, more chance of an induced dipole. 4

Dipole-dipole interactions

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Dipole-dipole interactions• Polar molecules exhibit these forces.

• (also exhibit LDFs)• Due to permanent dipoles.• Stronger IMFs than LDFs (given similar sized molecules).

• Some polar molecules (such as H2O) exhibit a special kind of dipole-dipole interaction.

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Water is a Liquid!

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Hydrogen Bonding in Water

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Clicker QuestionHow many of the following interactions does CH3CH2CH3 exhibit?

London dispersion

dipole-dipolehydrogen bonding

A) 0 B) 1C) 2D)3

Clicker QuestionHow many of the following interactions does CH3CH2OH exhibit?

London dispersion

dipole-dipolehydrogen bonding

A) 0 B) 1C) 2D)3

Clicker QuestionHow many of the following interactions does CH3OCH3 exhibit?

London dispersion

dipole-dipolehydrogen bonding

A) 0 B) 1C) 2D)3

Clicker Question

How do you think the molecules rank with respect to boiling point?

A) CH3CH2CH3 > CH3OCH3 > CH3CH2OH

B) CH3CH2CH3 > CH3CH2OH > CH3OCH3

C) CH3CH2OH > CH3CH2CH3 > CH3OCH3

D) CH3CH2OH > CH3OCH3 > CH3CH2CH3

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Ion-ion interactions• Ionic compounds exhibit these forces.

• Due to ions.• Strongest of the IMFs (given similar sized molecules).

• Example includes sodium chloride (NaCl).

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Clicker QuestionWhich of the following molecules exhibits dipole-dipole interactions?

a) OF2

b)SF6

c) XeF4

d)C2H2

e) At least two of the above molecules (a-d) exhibit dipole-dipole interactions. 14

Clicker QuestionWhich of the following molecules would be expected to have the lowest boiling point?

a) C4H10

b) NH3

c) H2O

d) C2H6

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Clicker QuestionMethane (CH4) is a gas, but carbon tetrachloride (CCl4) is a liquid at room conditions. Which of the following explains this phenomenon?

a) CCl4 is a polar molecule and CH4 is not.

b) CCl4 and CH4 have different geometries and shapes.

c) CH4 exhibits hydrogen bonding and CCl4 does not.

d) Cl is more electronegative than H. e) None of the above explanations explains this.

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Clicker QuestionWhich of the following molecules would be expected to have the highest melting point?

a) CO2

b)N2

c) SO2

d)H2

e) H2O 17