AP Chemistry (College Board): complete guide to the nine units, the science practices and the exam
A complete guide to College Board AP Chemistry. Covers the nine units (from atomic structure to equilibrium and acids and bases), the six science practices, how Section I (multiple choice) and Section II (free response) work, the equations and periodic table you are given, and how to study each unit for a 5.
College Board AP Chemistry is designed to be the equivalent of a first-year, two-semester general chemistry course for science majors. The course is built on a set of big ideas and six science practices, and the content is organized into nine units. There is no coursework, but laboratory and quantitative skills are examined directly in both sections of the exam. This page is the index: below is a map of the nine units, the exam structure, and how to study each one. This release covers all nine units in full.
The nine AP Chemistry units
The College Board organizes the content into nine units. Each carries an exam weighting (the share of multiple-choice questions it tends to contribute).
- Unit 1 Atomic Structure and Properties (7 to 9%)
- The mole and molar mass, mass spectra and average atomic mass, percent composition and empirical and molecular formulas, the composition of mixtures, electron configuration and the Coulombic model, photoelectron spectroscopy, periodic trends, and valence electrons and the ions elements form.
- Unit 2 Molecular and Ionic Compound Structure and Properties (7 to 9%)
- Ionic, covalent and metallic bonding, electronegativity and bond polarity, the potential-energy curve and bond strength, the structure of ionic solids and lattice energy, the electron-sea model and alloys, Lewis diagrams, resonance and formal charge, and VSEPR geometry and hybridization.
- Unit 3 Intermolecular Forces and Properties (18 to 22%)
- Intermolecular forces, solids, liquids, gases, the ideal gas law, solutions and concentration, and spectroscopy and the interaction of light with matter.
- Unit 4 Chemical Reactions (7 to 9%)
- Types of reactions, net ionic equations, representations of reactions, physical and chemical changes, stoichiometry, and oxidation-reduction reactions.
- Unit 5 Kinetics (7 to 9%)
- Reaction rates, rate laws, the rate-determining step, reaction mechanisms, collision theory, catalysis, and the effect of temperature.
- Unit 6 Thermodynamics (7 to 9%)
- Endothermic and exothermic processes, enthalpy, heat transfer and calorimetry, Hess's law, and bond and lattice energies.
- Unit 7 Equilibrium (7 to 9%)
- Dynamic equilibrium, the equilibrium constant, the reaction quotient, Le Chatelier's principle, and solubility equilibria.
- Unit 8 Acids and Bases (11 to 15%)
- pH and pOH, acid and base strength, buffers, titrations, and the acid-base properties of salts.
- Unit 9 Applications of Thermodynamics (7 to 9%)
- Entropy, Gibbs free energy and spontaneity, the relationship between free energy and equilibrium, and electrochemistry.
Exam structure
The AP Chemistry exam is 3 hours and 15 minutes and has two equally weighted sections. A calculator is allowed throughout, and you are given a periodic table and a formula and constants sheet.
- Section I, multiple choice - 60 questions, 1 hour 30 minutes, 50%. Discrete questions and question sets, many built on data, particulate diagrams or graphs.
- Section II, free response - 7 questions, 1 hour 45 minutes, 50%. Three long FRQs and four short FRQs, drawing on the six science practices.
The free-response questions ask you to represent and interpret models, design investigations, represent and analyze data, carry out calculations, and construct evidence-based arguments using AP task verbs (Justify, Calculate, Explain, Predict, Identify, Represent).
How to study AP Chemistry
AP Chemistry rewards particulate-level reasoning, structure-to-property thinking, and confident quantitative work.
- Work from the Course and Exam Description. Each topic (for example 1.7 Periodic Trends) maps to specific learning objectives and essential-knowledge statements that exam questions are written from.
- Reason from structure to properties. The recurring move is to explain a macroscopic property (melting point, conductivity, polarity) from the underlying atomic or molecular structure.
- Master the quantitative toolkit. The mole, molar mass, percent composition, and stoichiometry recur everywhere; get them automatic now.
- Use Coulomb's law as a thread. Effective nuclear charge, bond strength and lattice energy all come back to the attraction between charges.
- Rehearse the FRQ format. Time yourself on long and short free-response questions, and make every claim include evidence and chemical reasoning.
The units, topic by topic
Each topic has a Course-and-Exam-Description-level answer page with worked exam questions and cross-links, plus an overview guide and quiz. This release covers all nine units in full:
- Unit 1: moles and molar mass, mass spectra of elements, elemental composition of pure substances, composition of mixtures, atomic structure and electron configuration, photoelectron spectroscopy, periodic trends, valence electrons and ionic compounds.
- Unit 2: types of chemical bonds, intramolecular force and potential energy, structure of ionic solids, structure of metals and alloys, Lewis diagrams, resonance and formal charge, VSEPR and bond hybridization.
- Unit 3: intermolecular forces, properties of solids, solids, liquids and gases, ideal gas law, kinetic molecular theory, deviation from ideal gas law, solutions and mixtures, representations of solutions, separation of solutions and mixtures, solubility, spectroscopy and the electromagnetic spectrum, photoelectric effect, Beer-Lambert law.
- Unit 4: introduction for reactions, net ionic equations, representations of reactions, physical and chemical changes, stoichiometry, introduction to titration, types of chemical reactions, introduction to acid-base reactions, oxidation-reduction reactions.
- Unit 5: reaction rates, introduction to rate law, concentration changes over time, elementary reactions, collision model, reaction energy profile, introduction to reaction mechanisms, reaction mechanism and rate law, pre-equilibrium approximation, multistep reaction energy profile, catalysis.
- Unit 6: endothermic and exothermic processes, energy diagrams, heat transfer and thermal equilibrium, heat capacity and calorimetry, energy of phase changes, introduction to enthalpy of reaction, bond enthalpies, enthalpy of formation, Hess's law.
- Unit 7: introduction to equilibrium, direction of reversible reactions, reaction quotient and equilibrium constant, calculating the equilibrium constant, magnitude of the equilibrium constant, properties of the equilibrium constant, calculating equilibrium concentrations, representations of equilibrium, introduction to Le Chatelier's principle, reaction quotient and Le Chatelier's principle, introduction to solubility equilibria, common-ion effect, pH and solubility, free energy of dissolution.
- Unit 8: introduction to acids and bases, pH and pOH of strong acids and bases, weak acid and base equilibria, acid-base reactions and buffers, acid-base titrations, molecular structure of acids and bases, pH and pKa.
- Unit 9: introduction to entropy, absolute entropy and entropy change, Gibbs free energy and thermodynamic favorability, thermodynamic and kinetic control, free energy and equilibrium, free energy of dissolution, coupled reactions, galvanic and electrolytic cells, cell potential and free energy, cell potential under nonstandard conditions, electrolysis and Faraday's law.
You can also work through the stoichiometry and chemical calculations skills guide and its paired quiz.
For the official Course and Exam Description
The College Board publishes the full Course and Exam Description, released free-response questions, scoring guidelines and the equations sheet at apcentral.collegeboard.org. Always study from the current Course and Exam Description and the College Board's own released exams, because question style and the science practices are board-specific.
Chemistry guides
In-depth written guides with paired practice quizzes.
Chemistry practice quizzes
Multiple-choice drills with worked answer explanations. Your scores stay on this device.
The AP system, explained
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