Water and Intermolecular Forces: In-depth Notes

Understanding Water and its Molecular Properties

• Molecular Geometry of Water
  • Water (H2O) has a bent geometry, resulting from the arrangement of its hydrogen and oxygen atoms.
  • Water is a polar molecule, meaning it has a partial positive charge on one end (hydrogens) and a partial negative charge on the other end (oxygen).

Forces of Attraction in Water

• Intermolecular Forces of Attraction (IMFA)
  • IMFA refers to the attractive forces between molecules, also known as van der Waals forces.
  • There are three primary types of IMFA in water:
  1. London Dispersion Forces (LDF):
     • Present in all molecules.
     • Caused by fluctuations in electron distribution.
     • Weakest type of intermolecular force.
  2. Dipole-Dipole Forces:
     • Attractive forces between polar molecules due to dipole interactions.
     • Moderately strong type of IMFA.
  3. Hydrogen Bonding:
     • Stronger form of dipole-dipole interaction between hydrogen and electronegative atoms like O, N, or F.
     • Key in properties of water.

Water as a Universal Solvent

• The principle of solubility states that "like dissolves like."
• Polar solutes dissolve in polar solvents - e.g., sucrose in water.

Properties of Water Compared to Other Compounds

• Melting and Boiling Points
  • Water Melting Point: 0°C
  • Water Boiling Point: 100°C
  • Compared to carbon dioxide:
    • Melting Point: -56.6°C
    • Boiling Point: 78.5°C

Effects of IMFA on Physical Properties

• Melting Point:
  • Stronger IMFA lead to higher melting points; more energy required to break molecular bonds.
• Boiling Point:
  • Analogous to melting point, stronger IMFA means higher boiling points.
• Surface Tension:
  • Liquid with stronger IMFA exhibits higher surface tension due to greater cohesive forces.

Application of IMFA in States of Matter

• Strong IMFA lead to condensed phases (solids or liquids) while weak IMFA promote gases at room temperature.

Biomolecules Related to Water Properties

• Various biomolecules like proteins, carbohydrates, lipids, and nucleic acids exhibit properties impacted by water and intermolecular attraction.

Example of Biomolecules

• Proteins: Enzymes are proteins that catalyze chemical reactions and depend on water's properties for functioning.
• Carbohydrates: Provide energy and are impacted by the solubility in water.
• Lipids: Nonpolar biomolecules that interact with water differently, affecting biological membranes.
• Nucleic Acids (DNA/RNA): Structure and function rely on interactions with water under biological conditions.