Slide 1 Intermolecular Forces: - Attractive forces between molecules and ions, based on polarity -...

Slide 1

Intermolecular Forces:Intermolecular Forces:

- Attractive forces between molecules and ions, based on polarity

- Determine bulk properties of matter example – solid vs. liquid vs. gas

- Much weaker than intramolecular forces such as covalent bonds and ionic bonds

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Intermolecular Forces 01Intermolecular Forces 01

Type of Intermolecular Forces:

Dipole–dipole

Hydrogen Bonds

London Force (instantaneous induced dipole)

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Intermolecular Forces 03Intermolecular Forces 03

Ion–Dipole: Between polar molecules and ions.“opposites attract”

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Intermolecular Forces 02Intermolecular Forces 02

Dipole–Dipole: Between polar molecules.

Polar molecules:

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Hydrogen Bond: Molecules containing N–H, O–H, or F–H groups, and an electronegative O, N, or F.

This type of dipole-dipole force is especially strong, since the partial positive charge on H is high.

The H on the electronegative element is δ+, and is strongly attracted to the lone pair of electrons in a different molecule.

Intermolecular Forces 05Intermolecular Forces 05

H-bonding is a special type of dipole-dipole force that is especially strong.

It is an intermolecular force,

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Hydrogen Bond: Molecules containing N–H, O–H, or F–H groups, and an electronegative O, N, or F.

Intermolecular Forces 05Intermolecular Forces 05

Strength of hydrogen bonds can be observed by looking at boiling points of various compounds.

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Boiling points for different compounds of Group 4A, 5A, and 6A.

Intermolecular Forces 05Intermolecular Forces 05

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Intermolecular Forces 04Intermolecular Forces 04

The element bromine is a liquid, composed of Br2 molecules.

A moleculeof Br2

Bromine is a liquid, but non-polar. What holds bromine molecules together as a liquid?

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Intermolecular Forces 04Intermolecular Forces 04

London Dispersion Forces: Attraction is due to instantaneous, temporary dipoles formed due to electron motion.

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What intermolecular forces will operate between molecules in the substances below?

Review:

Cl2 CH3OCH3 Cl-NH2

Ar

CH3CH2CH3 HO

H HS

H

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Intermolecular Forces 06Intermolecular Forces 06

veryveryweak

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Intermolecular Forces 07Intermolecular Forces 07

CH4 110 K

SiH4 160 K

GeH4 175 K

SnH4 215 K

H2O 373 K *

H2S 215 K

H2Se 225 K

H2Te 270 K

Effect on Boiling PointEffect on Boiling Point

Force:

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Intermolecular Forces 08Intermolecular Forces 08

Surface Tension is the resistance of a liquid to spread out and increase its surface area.

Surface tension results from intermolecular force differences between molecules in the interior of a liquid and those on the surface.

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Intermolecular Forces 09Intermolecular Forces 09

Viscosity is the measure of a liquid’s resistance to flow. It is related to the ease with which molecules move around and thus to intermolecular forces.

High Viscosity Low Viscosity

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Phase Changes 01Phase Changes 01

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Phase Changes 02Phase Changes 02

Molar Heat of Fusion (∆Hfus):

The energy required to melt one mole of solid (in kJ).

Molar Heat of Vaporization (∆Hvap):

The energy (in kJ) required to vaporize one mole of liquid.

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Phase Changes 02Phase Changes 02

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Phase Changes 04Phase Changes 04

Sublimation: The process in which molecules go

directly from the solid into the vapor phase.

Deposition: The process in which molecules go directly from the vapor into the solid phase.

Molar heat of sublimation (∆Hsub): The energy (kJ)

required to sublime one mole of solid.

Hsub = H fus + Hvap

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Phase Changes 06Phase Changes 06

Vapor Pressure: The pressure exerted by gaseous molecules above a liquid.