Intermolecular Forces of Attraction

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Slide 1

Intermolecular Forces of Attraction

Slide 2

CA Standards

Students know the atoms and molecules in liquids move in a random pattern relative to one another because the intermolecular forces are too weak to hold the atoms or molecules in a solid form.

Slide 3

Intermolecular Forces

Forces that attract molecules to other molecules. These include:

Hydrogen bonding

Dipole-dipole attraction

London dispersion forces

Slide 4

Relative Magnitudes of Forces

The types of bonding forces vary in their strength as measured by average bond energy.

Covalent bonds (400 kcal)

Hydrogen bonding (12-16 kcal )

Dipole-dipole interactions (2-0.5 kcal)

London forces (less than 1 kcal)

Strongest

Weakest

Slide 5

Hydrogen Bonding

Bonding between hydrogen and more electronegative neighboring atoms such as oxygen and nitrogen

Base pairing in DNA by hydrogen bonding

Slide 6

Hydrogen Bonding in Water

Slide 7

Polarity

A molecule, such as HF, that has a center of positive charge and a center of negative charge is said to be polar, or to have a dipole moment.

H

F

+

-

Slide 8

Dipole-Dipole Attraction

Attraction between oppositely charged regions of neighboring molecules.

Dipole-dipole attraction in hydrogen chloride, a gas that is used to make hydrochloric acid

Slide 9

London (Dispersion) Forces

The weakest of intermolecular forces, these forces are proportional to the mass of the molecule

These are the only forces of attraction between completely nonpolar molecules

Large nonpolar molecules may have substantial dispersion forces, resulting in relatively high boiling points

Small nonpolar molecules have weak dispersion forces and exist almost exclusively as gases

Slide 10

London Forces in Hydrocarbons