Lecture Notes: Intermolecular Forces - Focus on Water (H2O) and Carbon Dioxide (CO2)

Overview

• Objective: Analyze intermolecular forces (IMFs) in water (H2O) and carbon dioxide (CO2).
• Main Focus: Question six on worksheet concerning identification of IMFs.

Types of Intermolecular Forces (IMFs)

1. Dipole-Dipole Forces
2. Hydrogen Bonding: A subset of dipole-dipole forces.
3. London Dispersion Forces (LDF)

Conditions for IMFs

• Nonpolar Molecules: Experience only London dispersion forces.
• Polar Molecules: Can experience dipole-dipole forces or hydrogen bonding.
  • Hydrogen Bonding: Occurs when hydrogen (H) is bonded to nitrogen (N), oxygen (O), or fluorine (F).

Water (H2O) Analysis

Lewis Dot Diagram

• Oxygen (O) has 6 valence electrons.
• Structure: Bent with two hydrogen atoms bonded.

Polarity and Charges

• Polar Bonds: Due to a significant electronegativity difference between H and O.
  • Electrons are pulled toward the more electronegative oxygen, creating partial negative charges on oxygen and partial positive on hydrogens.
• Polar Molecule: Polar bonds do not cancel out.

Intermolecular Forces in Water

• IMF Present: Hydrogen bonding.
• Reasoning:
  • Polar molecule with H bonded to O.
  • Intermolecular forces involve attractions between opposite charges on separate molecules.

Carbon Dioxide (CO2) Analysis

Lewis Dot Diagram

• Carbon (C) has 4 valence electrons.
• Structure: Linear with double bonds between C and each O.

Polarity and Charges

• Polar Bonds: Electrons are pulled towards oxygen due to higher electronegativity.
• Nonpolar Molecule: Polar bonds cancel out due to linear structure (opposite directions).

Intermolecular Forces in CO2

• IMF Present: London dispersion forces.
• Reasoning:
  • Nonpolar molecule, thus only LDFs are present as no dipole-dipole or hydrogen bonding can occur.

Conclusions

• Water (H2O): Exhibits hydrogen bonding due to its polar nature and presence of H-O bonds.
• Carbon Dioxide (CO2): Exhibits only London dispersion forces due to its nonpolar nature despite having polar bonds.