4: Secondary Bonding

Secondary Bonding

Overview

• Secondary bonding refers to interactions that occur between molecules due to dipolar attractions.

  • Includes van der Waals forces.

  • Can involve instantaneous, induced, or permanent dipoles.

  • Hydrogen bonding is a significant type of secondary bonding.

Hydrogen Bonding

• Hydrogen bonds occur when hydrogen combines with highly electronegative elements, resulting in strong dipoles.

  • Example: Water (H2O).

  • Strong dipoles are formed due to the difference in electronegativity between hydrogen and oxygen.

  • Electronegativity difference calculation: 3.16 (Cl) - 2.20 (H) = 0.96.

Water Molecule Structure

• Water is an example of a molecule exhibiting hydrogen bonding.

  • Structure is described as H-O-H (two hydrogen atoms bonded to one oxygen atom).

  • Illustrates how hydrogen bonds form between water molecules due to strong dipole interactions.

Polar and Non-Polar Molecules

• Molecules can be classified as polar or non-polar based on their dipole moments.

  • Polar molecules occur when there is a significant difference in electronegativity, creating a permanent dipole.

  • Non-polar molecules occur when the electronegativity difference is negligible, resulting in uniform electron distribution.

Characteristics of Secondary Bonds

• Secondary bonds are generally much weaker than primary bonds (covalent and ionic bonds).

  • Features include:

    • Low bond stiffness.

    • Lower melting points.

• Secondary bonding plays a vital role in the behavior of thermoplastic polymers, influencing their material properties.

Summary of Secondary Bonding

• Secondary bonds, specifically hydrogen bonding, are crucial for understanding molecular interactions.

• Despite being weaker than primary bonds, they have significant implications in material behavior and properties.