Lecture 11-IMF

Page 1: Lecture Overview

• Lecture 11: Introduction to Intermolecular Forces.

Page 2: Exam Results

• Exam 1 Results: Raw and scaled scores to be posted in the Atlas gradebook by afternoon.

• For missed questions summary, visit: Scantron results.

• Note: Incorrect UIN/NetID means no error sheet.

Page 3: Addressing Exam Struggles

• Talk Title: "My First Chemistry Exam Did Not Go Well, Now What?"

• Focus: Understanding why students struggle in chemistry; it may not be hard material but lack of preparation strategies.

• Details: Time management and application of study skills.

• Professor: Dr. Ray from Chem 104.

• Dates & Location: February 27 (4:00 pm, 1000 Lincoln Hall) and March 5 (4:00 pm, 1092 Lincoln Hall).

Page 4: Upcoming Assignments

• Quiz 3: Due March 9, covering intermolecular forces and assignments from week 7.

• Quiz 4: Due March 27.

• Lon Capa HW 6: Due March 4, focusing on intermolecular forces.

• HW 7: Due March 11.

Page 5: Boiling Points of Substances

• Substance Boiling Points:

  • NaCl: 1413°C

  • H2O: 100°C

  • CH4: -164°C

Page 6: Forces Overview

• Intramolecular Forces: Bonds within a molecule (hold atoms together).

• Intermolecular Forces (IMF): Attraction between neighboring molecules (keeps them together in liquid/solid phases).

Page 9: Physical States of Matter

• Physical State Determined by IMF Strength:

  • Gas: No IMF (e.g., N2 at 298 K).

  • Solid: Strong IMF (e.g., NaCl at 298 K).

  • Liquid: Intermediate IMF (e.g., H2O at 298 K).

Page 10: Phase Changes

• Phase Change Mechanism: Involves breaking/forming of intermolecular forces.

• Example: 15% IMF broken during solid to liquid transition; 85% during liquid to gas transition.

Page 12: Physical Properties Related to IMF Strength

• Key Physical Properties:

  • Normal Boiling Point: Temp where liquid to gas transition occurs at 1 atm.

  • Normal Freezing Point: Temp where liquid to solid transition occurs at 1 atm.

  • Molar Heat of Vaporization: Energy to boil 1 mole of a liquid (H2O: ΔHvap = 40.6 kJ/mol).

  • Molar Heat of Fusion: Energy to melt 1 mole of solid (H2O: ΔHfus = 6.02 kJ/mol).

  • As IMF strength increases, these properties increase.

Page 15-17: Vapor Pressure

• Definition: Equilibrium pressure of gas over liquid at given temperature.

• Relationship with IMF:

  • Inversely related to strength of IMF; stronger IM forces result in lower vapor pressure.

  • Directly related to temperature; higher temperature increases vapor pressure.

• Vapor Pressure Table for Water:

  • 25°C: 24 torr

  • 40°C: 55 torr

  • 70°C: 240 torr

  • 100°C: 760 torr

Page 20-22: Types of Intermolecular Forces

• A. Ionic Forces: Holds ionic compounds together, much stronger than other IM forces.

• B. Covalent Forces: Attractive forces for covalent compounds in solid/liquid phases.

  • Types include Dipole-dipole, Hydrogen bonding, and London Dispersion forces.

Page 24-26: Dipole-Dipole Forces

• Definition: Attractive forces between polar covalent compounds.

Page 27-30: Hydrogen Bonding

• Definition: Special type of dipole-dipole interaction, the strongest covalent IM force.

• Hydrogen must be covalently bonded to F, O, or N for H-bonding to occur.

• High boiling point and low vapor pressure are characteristic of substances able to hydrogen bond.

Page 33-35: London Dispersion Forces

• Definition: Due to accidental or induced dipoles; prevalent in all covalent compounds.

• Affect strength based on size and shape of the molecule; larger and more elongated molecules have stronger LD forces.