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      • Introduction
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      • Writing Equilibrium Expressions
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      • Acids and Bases Worksheet + Answers
      • Arrhenius vs Bronsted-Lowry vs Lewis Acids
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      • Phase Diagrams
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      • Effects of Intermolecular Forces
      • Ranking by Boiling/Melting Point
      • Clausius-Clapeyron Equation
      • Heating Curves
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    • Organic Reactions >
      • Br2 + Alkene (Adding across a double bond)
      • HCl + Alkene (Adding across a double bond)
      • Reaction of OH with Alkyl Halide
      • What is Regioselectivity?
    • Moles and Mass >
      • Average Atomic Mass
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      • Percent Composition
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      • What's in an Atom?
      • Quantum Numbers
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      • Light: E h ν λ
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    • Organic Naming >
      • Naming Organic Molecules
      • How to Name Amines
      • How to Name Amides
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  • Lewis Structures
  • Home / Ask Me Stuff
  • Lessons
    • Thermodynamics >
      • Thermochemistry Worksheet + Answers
      • First Law of Thermodynamics
      • Pressure-Volume Work
      • Enthalpy
      • Hess' Law
      • Enthalpy of Formation
      • Heat Capacity
      • Calorimetry
      • Entropy
      • Third Law of Thermodynamics
      • Spontaneity: Gibbs Free Energy
      • Second Law of Thermodynamics
      • Spontaneity at Different Temperatures
    • Electrochemistry >
      • Redox Reactions
      • Introduction to Half-Reactions
      • Calculating Oxidation Number
      • Has a Redox Reaction Occurred?
      • How to Balance Redox Reactions (Acidic Solution)
      • How to Balance Redox Reactions (Basic Solution)
      • Galvanic Cells
      • Standard Reduction Potentials
      • Electrolytic Cells
      • Nernst Equation
    • Kinetics >
      • Introduction
      • Relative Rates of Reaction
      • Rate Laws
      • Zero-Order Reactions
      • First-Order Reactions
      • Second-Order Reactions
      • Half-Life Expressions
      • Arrhenius Equation
      • How Long will it Take to Decay?
      • What Order is this Reaction?
      • Find the Rate Constant
      • Find the Activation Energy
    • Gases >
      • Pressure, Volume, Temperature
      • Ideal Gas Law
      • Density of Gases
      • Ideal Gas Law and Changes in P, V, T
      • Kinetic Molecular Theory
      • van der Waals' Equation for Non-Ideal Gases
      • Partial Pressures
      • Kinetic Energy and Temperature
    • Equilibrium >
      • Writing Equilibrium Expressions
      • Le Chatelier's Principle
    • Acids and Bases >
      • Acids and Bases Worksheet + Answers
      • Arrhenius vs Bronsted-Lowry vs Lewis Acids
      • Solve Titration Questions
    • Intermolecular Forces >
      • Phase Diagrams
      • Phase Changes
      • Intermolecular Forces
      • Effects of Intermolecular Forces
      • Ranking by Boiling/Melting Point
      • Clausius-Clapeyron Equation
      • Heating Curves
    • Solids >
      • Ionic/Metallic/Covalent
      • Symmetry of Solids
      • Simple Cubic, fcc and bcc
      • How to Find Edge Length
    • Organic Reactions >
      • Br2 + Alkene (Adding across a double bond)
      • HCl + Alkene (Adding across a double bond)
      • Reaction of OH with Alkyl Halide
      • What is Regioselectivity?
    • Moles and Mass >
      • Average Atomic Mass
      • Solve for Isotopic Abundance
      • Limiting Reagents
      • Percent Yield
      • Actual Yield and Percentage Yield
      • Percent Composition
    • Atomic Structure >
      • What's in an Atom?
      • Quantum Numbers
      • Pauli, Aufbau, Hund
      • Light: E h ν λ
      • Energy Levels of Hydrogen
      • Energy Levels of Non-Hydrogen Atoms
    • Organic Naming >
      • Naming Organic Molecules
      • How to Name Amines
      • How to Name Amides
  • Privacy Policy
  • Lewis Structures

Effects of Intermolecular Forces


Intermolecular forces control how well molecules stick together. This affects many of the measurable physical properties of substances:

Melting and Boiling Points
  • If molecules stick together more, they'll be tougher to break apart
  • Stronger intermolecular forces → higher melting and boiling points

Viscosity
  • Viscosity is a measure of how well substances flow.
  • Stronger intermolecular forces → higher viscosity.

Surface Tension
  • Surface tension is a measure of the toughness of the surface of a liquid
  • Stronger intermolecular forces → higher surface tension.

Vapour Pressure
  • This is a small amount of gas that is found above all liquids. Refer to our lesson about vapour pressure to learn about it.
  • Stronger intermolecular forces → Lower vapour pressure.

Answering Questions about Intermolecular Force Strength

These are one of my favourite types of questions. If you are asked to rank molecules in order of melting point, boiling point, viscosity, surface tension or vapour pressure ... what they are actually asking is for you to rank them by strength of intermolecular forces (either increasing or decreasing).

Here is my strategy for this:

  1. Look for molecules with hydrogen bonding.  They will have the strongest intermolecular forces.

  2. Look for molecules with dipoles. These will have the next strongest intermolecular forces.

  3. Larger molecules will have stronger London dispersion forces. These are the weakest intermolecular forces but will often be the deciding factor in multiple choice questions.


I have created a worksheet showing how I answer these types of questions:
Sample Questions: Ranking Substances by Melting Point, Boiling Point, Surface Tension, Visoosity, or Vapour Pressure
File Size: 67 kb
File Type: pdf
Download File

Created by Nathan Oldridge (aka ChemistNATE).  All lessons here are Public Domain.