🧪AP Chemistry Subject Guides

Key Concepts

• Matter consists of atoms which are the building blocks of all substances
• Elements are pure substances that cannot be broken down into simpler substances through chemical means
• Compounds form when two or more elements chemically combine in specific ratios
• Chemical reactions involve the rearrangement of atoms to form new substances
• Stoichiometry deals with the quantitative relationships between reactants and products in a chemical reaction
• Kinetics studies the rates of chemical reactions and the factors that influence them
• Equilibrium occurs when the rates of forward and reverse reactions are equal resulting in no net change in concentrations
• Thermodynamics examines the energy changes associated with chemical reactions and physical processes

Atomic Structure and Periodicity

• Atoms consist of protons and neutrons in the nucleus surrounded by electrons in orbitals
• Protons have a positive charge neutrons are neutral and electrons have a negative charge
• The atomic number represents the number of protons in an atom determining the element's identity
• Isotopes are atoms of the same element with different numbers of neutrons
• Electron configuration describes the arrangement of electrons in an atom's orbitals
  • Electrons fill orbitals in order of increasing energy (1s 2s 2p 3s 3p 4s 3d etc.)
  • The Aufbau principle Hund's rule and the Pauli exclusion principle govern electron configuration
• The periodic table organizes elements based on their atomic number and electron configuration
  • Elements in the same group (column) have similar chemical properties due to their valence electron configuration
  • Periodic trends (atomic radius ionization energy electronegativity etc.) can be explained by the arrangement of electrons

Chemical Bonding and Molecular Geometry

• Chemical bonds form when atoms share or transfer electrons to achieve a stable electron configuration
• Ionic bonds involve the transfer of electrons from one atom to another forming ions with opposite charges
  • Ionic compounds have high melting points and are good conductors of electricity when molten or in solution
• Covalent bonds involve the sharing of electrons between atoms
  • Nonpolar covalent bonds occur when electrons are shared equally (H2 Cl2)
  • Polar covalent bonds occur when electrons are shared unequally due to differences in electronegativity (HCl H2O)
• Metallic bonds involve the delocalization of valence electrons creating a "sea" of electrons surrounding metal cations
• Lewis structures represent the arrangement of atoms and electrons in a molecule or polyatomic ion
• VSEPR (Valence Shell Electron Pair Repulsion) theory predicts the geometry of molecules based on the number of electron domains around the central atom
  • Electron domains include bonding pairs and lone pairs of electrons
  • Molecular geometries include linear trigonal planar tetrahedral trigonal bipyramidal and octahedral

Stoichiometry and Reactions

• Stoichiometry involves calculating the quantities of reactants and products in a chemical reaction
• Balanced chemical equations show the relative numbers of reactant and product molecules
• Mole ratios derived from the balanced equation are used to convert between quantities of reactants and products
• Limiting reactants determine the maximum amount of product that can be formed in a reaction
• Percent yield compares the actual yield of a reaction to the theoretical yield
• Types of chemical reactions include synthesis decomposition single displacement double displacement and combustion
• Oxidation-reduction (redox) reactions involve the transfer of electrons between species
  • Oxidation is the loss of electrons and reduction is the gain of electrons
  • Oxidation numbers are used to keep track of electron transfer in redox reactions

Kinetics and Equilibrium

• Kinetics studies the rates of chemical reactions and the factors that influence them
• Reaction rate is the change in concentration of a reactant or product per unit time
• Factors affecting reaction rate include concentration temperature pressure surface area and catalysts
• Rate laws express the relationship between reaction rate and reactant concentrations
  • The order of a reaction with respect to a reactant is the power to which its concentration is raised in the rate law
  • The overall order of a reaction is the sum of the orders with respect to each reactant
• Reaction mechanisms describe the step-by-step process by which a reaction occurs
  • The slowest step in a multi-step reaction is the rate-determining step
• Equilibrium is a dynamic state in which the rates of forward and reverse reactions are equal
• The equilibrium constant (K) expresses the relationship between reactant and product concentrations at equilibrium
  • For a general reaction: $aA + bB \rightleftharpoons cC + dD$, $K = \frac{[C]^c[D]^d}{[A]^a[B]^b}$
• Le Châtelier's principle states that a system at equilibrium will shift to counteract any stress applied to the system
  • Stresses include changes in concentration pressure volume and temperature

Thermodynamics and Electrochemistry

• Thermodynamics deals with the energy changes associated with chemical reactions and physical processes
• The first law of thermodynamics states that energy is conserved; it can be converted from one form to another but cannot be created or destroyed
• Enthalpy (H) is a measure of the total heat content of a system
  • Exothermic reactions release heat and have negative ΔH values
  • Endothermic reactions absorb heat and have positive ΔH values
• Entropy (S) is a measure of the disorder or randomness of a system
  • Spontaneous processes are characterized by an increase in entropy of the universe
• Gibbs free energy (G) determines the spontaneity of a process at constant temperature and pressure
  • ΔG = ΔH - TΔS where T is the absolute temperature
  • Spontaneous processes have negative ΔG values
• Electrochemistry studies the interconversion of electrical and chemical energy
• Voltaic (galvanic) cells generate electricity from spontaneous redox reactions
  • The anode is the site of oxidation and the cathode is the site of reduction
  • The standard cell potential (E°cell) is the voltage produced by the cell under standard conditions (1 M concentrations 1 atm pressure 25°C)
• Electrolytic cells use electricity to drive nonspontaneous redox reactions
  • Electrolysis is used in electroplating and the production of pure metals from ores

Lab Techniques and Safety

• Proper lab techniques and safety practices are essential in chemistry
• Personal protective equipment (PPE) includes goggles gloves and lab coats
• Handling chemicals safely involves understanding their properties and potential hazards
  • Material Safety Data Sheets (MSDS) provide information on the hazards and proper handling of chemicals
• Measuring mass volume and temperature accurately is crucial for quantitative experiments
  • Balances pipettes graduated cylinders and thermometers are common measuring tools
• Separation techniques include filtration distillation chromatography and extraction
• Titration is a quantitative technique used to determine the concentration of an unknown solution
  • The endpoint is reached when the indicator changes color signaling the completion of the reaction
• Spectroscopy techniques (UV-Vis IR NMR etc.) are used to analyze the structure and composition of compounds
• Proper disposal of chemical waste is essential to prevent environmental contamination and health hazards

Exam Prep and Practice Problems

• Review key concepts and learning objectives from each unit
• Summarize important equations formulas and relationships
• Create a study schedule to manage your time effectively
• Practice solving a variety of problems to reinforce your understanding
  • Start with basic problems and gradually increase the difficulty level
  • Focus on topics that you find challenging or need more practice with
• Analyze and learn from your mistakes in practice problems
  • Identify areas where you need to improve your understanding or problem-solving skills
• Take practice exams under timed conditions to simulate the actual test experience
  • Familiarize yourself with the format structure and style of questions on the AP Chemistry exam
• Develop test-taking strategies such as:
  • Reading questions carefully and identifying key information
  • Eliminating incorrect answer choices
  • Managing your time effectively during the exam
• Collaborate with classmates to form study groups and discuss difficult concepts or problems
• Seek help from your teacher or tutor for clarification on topics you find challenging