AP Chemistry / Topic
Intermolecular Forces and Properties
Unit 3 connects particle-level forces to bulk properties: London dispersion, dipole-dipole, and hydrogen bonding, plus the gas laws, kinetic molecular theory, solutions and molarity, and spectroscopy. It is one of the most-weighted units on the exam.
What the exam asks
- Rank substances by boiling point, vapor pressure, viscosity, or surface tension using IMF strength
- Identify when hydrogen bonding applies (H bonded directly to N, O, or F)
- Apply the ideal gas law and Dalton's law of partial pressures
- Explain non-ideal gas behavior at high pressure and low temperature
- Work with molarity, dilutions, and particle diagrams of solutions
- Connect photon energy and wavelength to spectroscopy regions (Beer-Lambert law for absorbance)
Key formulas and rules
PV = nRT
P(total) = P1 + P2 + ...; Pi = Xi·P(total)
M = mol/L; M1V1 = M2V2
average KE ∝ temperature (K); lighter gases move faster at the same T
A = εbc — absorbance is proportional to concentration
H-bonding > dipole-dipole > London dispersion (but dispersion grows with molar mass and surface area)
Question bank breakdown
54
2
19 easy · 22 medium · 13 hard
Skills covered
Every question in the bank comes with a per-choice explanation, so you learn why each wrong answer is wrong — not just the key.
Sample question
From the free tier of the ScoreMint AP Chemistry bank — try it, then check the answer.
A sealed, rigid container holds 2.00 mol of an ideal gas at 300 K and 1.00 atm. If the temperature is increased to 450 K, what is the new pressure in the container?
- A. 0.67 atm
- B. 1.00 atm
- C. 1.50 atm
- D. 2.25 atm
Show answer and explanation
Answer: C. Correct. Since the container is rigid (constant volume) and sealed (constant moles), we use Gay-Lussac's Law: P₁/T₁ = P₂/T₂. P₂ = P₁ × (T₂/T₁) = 1.00 atm × (450 K / 300 K) = 1.00 × 1.50 = 1.50 atm. Alternatively, from PV = nRT with constant V and n: P is directly proportional to T. T increases by a factor of 1.5, so P does too. ✓
Study tip
Never say 'hydrogen bonds break inside the molecule' — on ranking questions, name the specific IMF between molecules and compare its strength; breaking covalent bonds is a different (and wrong) claim.