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Intermolecular Forces and Physical Properties: Step-by-Step Guidance

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Q1. List all types of IMFs that would occur in each of the following molecules:

  • NH3

  • SO2

  • CCl4

  • HF

Background

Topic: Intermolecular Forces (IMFs)

This question tests your ability to identify the types of intermolecular forces present in different molecules based on their structure and polarity.

Key Terms and Concepts:

  • London Dispersion Forces: Present in all molecules, especially nonpolar ones.

  • Dipole-Dipole Forces: Present in polar molecules.

  • Hydrogen Bonding: Occurs when H is bonded to N, O, or F.

Step-by-Step Guidance

  1. For each molecule, determine if it is polar or nonpolar by considering its shape and electronegativity differences.

  2. Identify if the molecule contains N-H, O-H, or F-H bonds, which are necessary for hydrogen bonding.

  3. List all IMFs present: all molecules have London dispersion forces; polar molecules also have dipole-dipole forces; molecules with N-H, O-H, or F-H have hydrogen bonding.

  4. For each molecule, write down the types of IMFs you identified, but do not finalize your list yet.

Try solving on your own before revealing the answer!

Q2. List the dominant (strongest) type of IMF for the pure substances, then rank the strength of each compound based on IMFs within the samples. Rank #1 for the strongest and #4 for the weakest.

  • HBr

  • O2

  • CH3OH

  • NaCl

Background

Topic: Ranking Intermolecular Forces

This question asks you to identify the strongest IMF present in each compound and then rank the compounds by the strength of their IMFs.

Key Terms and Concepts:

  • Ionic Bonds: Present in ionic compounds (e.g., NaCl).

  • Hydrogen Bonding: Strong IMF present in molecules with O-H, N-H, or F-H bonds.

  • Dipole-Dipole Forces: Present in polar molecules without hydrogen bonding.

  • London Dispersion Forces: Present in all molecules, dominant in nonpolar molecules.

Step-by-Step Guidance

  1. Identify the type of bonding or IMF for each compound (ionic, hydrogen bonding, dipole-dipole, or dispersion).

  2. Recall the general order of IMF strength: ionic > hydrogen bonding > dipole-dipole > dispersion.

  3. Assign the dominant IMF to each compound based on its structure and composition.

  4. Rank the compounds from strongest to weakest IMF, but do not finalize the ranking yet.

Try solving on your own before revealing the answer!

Q3. Rank the following compounds from lowest to highest surface tension. Explain your ranking, assuming every molecule will be in the liquid phase.

  • C2H6

  • CH3NH2

  • KCl

  • H3C – O – CH3

Background

Topic: Surface Tension and IMFs

This question tests your understanding of how intermolecular forces affect surface tension in liquids.

Key Terms and Concepts:

  • Surface Tension: The energy required to increase the surface area of a liquid, which increases with stronger IMFs.

  • IMF Strength: Stronger IMFs lead to higher surface tension.

Step-by-Step Guidance

  1. Identify the dominant IMF present in each compound.

  2. Recall that stronger IMFs result in higher surface tension.

  3. Arrange the compounds in order of increasing IMF strength.

  4. Use this order to rank the compounds from lowest to highest surface tension, but do not finalize the ranking yet.

Try solving on your own before revealing the answer!

Q4. Rank the following compounds from weakest intermolecular forces to strongest. Explain your ranking.

  • I2

  • H2S

  • H2O

Background

Topic: Comparing Intermolecular Forces

This question asks you to compare the strength of IMFs in different molecules and rank them accordingly.

Key Terms and Concepts:

  • London Dispersion Forces: Dominant in nonpolar molecules like I2.

  • Dipole-Dipole Forces: Present in polar molecules like H2S.

  • Hydrogen Bonding: Present in molecules like H2O.

Step-by-Step Guidance

  1. Determine the polarity and possible hydrogen bonding for each molecule.

  2. Assign the dominant IMF for each compound.

  3. Recall the general order: dispersion < dipole-dipole < hydrogen bonding.

  4. Rank the compounds from weakest to strongest IMF, but do not finalize the ranking yet.

Try solving on your own before revealing the answer!

Q5. From the molecules in question 4, rank each molecule from lowest to highest boiling point. Explain your ranking.

Background

Topic: Boiling Point and IMFs

This question tests your understanding of how the strength of IMFs affects boiling points.

Key Terms and Concepts:

  • Boiling Point: The temperature at which a liquid becomes a gas; higher IMFs lead to higher boiling points.

Step-by-Step Guidance

  1. Recall your ranking of IMF strength from question 4.

  2. Understand that higher IMF strength generally means a higher boiling point.

  3. Use your previous ranking to order the molecules by boiling point, but do not finalize the ranking yet.

Try solving on your own before revealing the answer!

Q6. From the molecules in question 4, rank each molecule from lowest to highest vapor pressure. Explain your ranking.

Background

Topic: Vapor Pressure and IMFs

This question tests your understanding of how IMF strength affects vapor pressure.

Key Terms and Concepts:

  • Vapor Pressure: The pressure exerted by a vapor in equilibrium with its liquid; stronger IMFs result in lower vapor pressure.

Step-by-Step Guidance

  1. Recall your ranking of IMF strength from question 4.

  2. Understand that higher IMF strength means lower vapor pressure.

  3. Use your previous ranking to order the molecules by vapor pressure, but do not finalize the ranking yet.

Try solving on your own before revealing the answer!

Q7. For each compound given, first draw their Lewis structure. Then, determine whether the molecule is polar or non-polar. Then write the strongest intermolecular force present in the space provided.

  • CH3Br

  • CH3NH2

  • K2O

  • H3C – O – CH3

  • CO2

  • SF6

  • OCS

Background

Topic: Lewis Structures, Polarity, and IMFs

This question tests your ability to draw Lewis structures, determine molecular polarity, and identify the strongest IMF present.

Key Terms and Concepts:

  • Lewis Structure: A diagram showing the bonding between atoms and lone pairs.

  • Polarity: Determined by molecular geometry and electronegativity differences.

  • IMFs: Identify the strongest IMF based on structure and polarity.

Step-by-Step Guidance

  1. Draw the Lewis structure for each compound, showing all bonds and lone pairs.

  2. Analyze the molecular geometry and electronegativity to determine if the molecule is polar or nonpolar.

  3. Based on polarity and presence of N-H, O-H, or F-H bonds, identify the strongest IMF present.

  4. Fill in the table with your findings, but do not finalize your answers yet.

Try solving on your own before revealing the answer!

Q8. From each of the following sets, select the molecule that would be expected to have a higher viscosity. Explain your choice, assuming every molecule will be in the liquid phase.

  • C7H16 and C5H12

  • CCl4 and CBr4

  • H2O and H2S

  • CH3CH2OH and H3C – O – CH3

Background

Topic: Viscosity and IMFs

This question tests your understanding of how molecular structure and IMFs affect viscosity.

Key Terms and Concepts:

  • Viscosity: Resistance to flow; increases with stronger IMFs and larger molecular size.

Step-by-Step Guidance

  1. For each pair, compare molecular size and IMF strength.

  2. Recall that larger molecules and those with stronger IMFs generally have higher viscosity.

  3. Identify which molecule in each pair is expected to have higher viscosity, but do not finalize your choices yet.

Try solving on your own before revealing the answer!

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