1.1.9

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.
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Principles of Science I

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Structure & Bonding

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Properties of Substances

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Cell Structure & Function

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Cell Specialisation

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Working with Waves

1.7

Waves in Communication

2

Practical Scientific Procedures and Techniques

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Science Investigation Skills

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Principles of Science II

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Extracting Elements

4.2

Relating Properties to use of Substances

4.3

Organic Chemistry

4.4

Energy Changes in Industry

4.5

The Circulatory System

4.6

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4.7

Urinary System

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4.9

Thermal Physics

4.10

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4.11

Fluids

5

Contemporary Issues in Science

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