1.3.9

Intermolecular Forces 2

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Permanent Dipole-Dipole Interactions

Permanent dipole-dipole interactions exist between two permanently polar molecules.

Permanent dipoles

Permanent dipoles

  • Permanent dipoles have a δ- on one side and a δ+ on the other.
  • The δ+ of one molecule will attract the δ- of another molecule.
    • This means that the molecules will line up throughout a liquid or solid in this fashion.
    • Permanent dipole-dipole forces are the second strongest molecular interaction.
Polar molecules

Polar molecules

  • Permanent dipole-dipole interactions are only possible in molecules that contain a permanent dipole.
    • So they are only found between polar molecules.

Hydrogen Bonds

Hydrogen bonds only exist between some specific types of molecules. These intermolecular forces are stronger than induced and permanent dipole-dipole interactions.

Hydrogen bonds

Hydrogen bonds

  • A hydrogen bond is the name given to a very strong permanent dipole-permanent dipole force.
  • With some elements, hydrogen can form extremely strong dipole-dipole interactions.
    • When these are strong enough to be considered a bond, it is called a hydrogen bond.
Where are hydrogen bonds found?

Where are hydrogen bonds found?

  • Hydrogen bonds are found when you have a hydrogen atom bonded to either oxygen, nitrogen, or fluorine.
  • That hydrogen atom will form a strong permanent dipole-dipole interaction with another oxygen, nitrogen, or fluorine atom.
  • Examples of liquids with hydrogen bonds are:
    • Water.
    • Hydrogen fluoride.
    • Ammonia.
Why do hydrogen bonds form?

Why do hydrogen bonds form?

  • When hydrogen is bonded to an extremely electronegative element, it develops a strong δ+ charge.
  • Hydrogen is a very small atom, so it has a high charge density in this situation.
    • This allows it to form a strong bond with any highly δ- charged atom.
Jump to other topics
1

Physical Chemistry

1.1

Atomic Structure

1.2

Amount of Substance

1.3

Bonding

1.4

Energetics

1.5

Kinetics

1.6

Equilibria

1.7

Redox

2

Physical Chemistry 2 (A2 Only)

3

Inorganic Chemistry

4

Inorganic Chemistry 2 (A2 Only)

5

Organic Chemistry 1

6

Organic Chemistry 2 (A2 Only)

6.1

Optical Isomerism (A2 Only)

6.2

Aldehydes & Ketones (A2 Only)

6.3

Carboxylic Acids & Esters (A2 Only)

6.4

Aromatic Chemistry (A2 Only)

6.5

Amines (A2 Only)

6.6

Polymers (A2 Only)

6.7

Biological Organic (A2 Only)

6.8

Organic Synthesis (A2 Only)

6.9

NMR Spectroscopy (A2 Only)

6.10

Chromatography (A2 Only)

6.11

A-A* (AO3/4) - Organic 2

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