Intermolecular Forces - Chapter 10

Intermolecular Forces Overview

• Intermolecular forces are attractions between molecules, influencing physical properties such as boiling points and solubility.

Types of Intermolecular Forces

• Hydrogen bonding: Strong type of dipole-dipole interaction when hydrogen is bonded to highly electronegative elements (N, O, F).
• Dipole-dipole interactions: Occur between polar molecules due to permanent dipoles.
• London dispersion forces (LDF): Weak forces present in all molecules, stronger in larger, more polarizable molecules.

Classification of Substances

• HF exhibits hydrogen bonding, dipole-dipole interactions, and London dispersion forces.
• HCl and CO show dipole-dipole interactions and London dispersion forces.
• CH4 is associated solely with London dispersion forces.

Molecular Properties and Interactions

• Only London dispersion forces are observed in He and Cl2.
• Only ClF and NF3 show polar interactions (dipole-dipole forces).
• Molecules that can hydrogen bond include HF and CH3OH.

Strength of Intermolecular Forces

• The strength of London dispersion forces varies by molecular size:
  • Largest molecules have the strongest interactions: C6H14 > C5H12 > C4H10.
• For small molecules with similar molar masses:
  • Hydrogen bonding is the strongest, followed by dipole-dipole interactions, then London dispersion forces.

Solubility in Different Solvents

• I2 is better solvated in carbon tetrachloride (CCl4), while Na2S and CH2O have better solubility in water (H2O).

Boiling Points and States of Matter

• The boiling point order for compounds is Hexane > Pentane > Neopentane.
• At 0 °C and 1 atm, ethanol exists as a liquid.

Behavior of Intermolecular Forces

• London dispersion forces generally increase in strength with increasing molecular weight.
• In compound H2NNH2, the strongest intermolecular force present is hydrogen bonding.

Key Molecular Comparisons

• CH3OH is the only molecule in certain groupings exhibiting hydrogen bonding, while CH3CH3 is expected to have the lowest boiling point among the listed compounds due to weaker intermolecular forces.

Test your knowledge on intermolecular forces in Chapter 10. This quiz covers the classification of substances like HF, CH4, and HCl based on the types of intermolecular forces they exhibit, including hydrogen bonding and London dispersion forces. Enhance your understanding of molecular interactions with these targeted questions.