AP® Chemistry

Pick a unit

• Unit 1

  7–9% of exam

  Atomic Structure and Properties

  8 topics · 47 videos

  • The mole links grams you can weigh to particles you can't count
  • A pure compound always has the same ratio of elements by mass
  • Coulomb's law explains how tightly electrons are held
  • Electron configurations explain periodic trends
  • An element's place in the periodic table predicts its ion's charge
  Open unit 1: Atomic Structure and Properties

• Unit 2

  7–9% of exam

  Compound Structure and Properties

  7 topics · 44 videos

  • Electronegativity difference decides how evenly electrons are shared
  • Bonds form where potential energy is lowest
  • Lewis diagrams show where the valence electrons are
  • Electron pairs spread out, which sets a molecule's shape
  • A substance's structure explains its properties
  Open unit 2: Compound Structure and Properties

• Unit 3

  18–22% of exam

  Properties of Substances and Mixtures

  13 topics · 74 videos

  • Stronger forces between particles mean higher boiling points
  • The kind of particles in a solid explains its properties
  • Ideal gases follow PV = nRT; real gases stray from it
  • Like dissolves like
  • A photon's energy matches the energy change it causes
  Open unit 3: Properties of Substances and Mixtures

• Unit 4

  7–9% of exam

  Chemical Reactions

  9 topics · 49 videos

  • Atoms and charge are conserved, so equations must balance
  • Net ionic equations show only the particles that actually change
  • Coefficients give the mole ratios behind every stoichiometry problem
  • Acid-base reactions transfer protons; redox reactions transfer electrons
  Open unit 4: Chemical Reactions

• Unit 5

  7–9% of exam

  Kinetics

  11 topics · 60 videos

  • The overall rate law comes from experiments, not from the balanced equation
  • Only collisions with enough energy and the right orientation react
  • The slowest step in a mechanism controls the overall rate
  • Catalysts speed reactions by opening a lower-energy pathway
  Open unit 5: Kinetics

• Unit 6

  7–9% of exam

  Thermochemistry

  9 topics · 52 videos

  • Energy is conserved: what the system loses, the surroundings gain
  • Breaking bonds takes energy; forming bonds releases it
  • Negative ΔH means exothermic; positive ΔH means endothermic
  • Reaction enthalpies can be reversed, scaled and added (Hess's law)
  Open unit 6: Thermochemistry

• Unit 7

  7–9% of exam

  Equilibrium

  12 topics · 62 videos

  • Equilibrium is dynamic: forward and reverse rates are equal, not zero
  • K describes the mixture at equilibrium; Q describes the mixture right now
  • Comparing Q with K tells you which way a reaction will go
  • A system at equilibrium shifts to partly undo any stress
  • How much a salt dissolves is an equilibrium described by Ksp
  Open unit 7: Equilibrium

• Unit 8

  11–15% of exam

  Acids and Bases

  11 topics · 55 videos

  • pH is a log scale of hydronium ion concentration
  • Strong acids and bases ionize completely; weak ones only partly
  • Titration curves reveal equivalence and half-equivalence points
  • Buffers resist pH change because they contain both members of a conjugate pair
  • Molecular structure explains why some acids are stronger than others
  Open unit 8: Acids and Bases

• Unit 9

  7–9% of exam

  Thermodynamics and Electrochemistry

  11 topics · 55 videos

  • Entropy increases when matter or energy spreads out
  • ΔG° = ΔH° − TΔS° decides whether a process is thermodynamically favored
  • Favored doesn't mean fast: a high activation energy can block a reaction
  • ΔG°, K and E°cell describe the same driving force
  • Galvanic cells release energy; electrolytic cells need energy put in
  Open unit 9: Thermodynamics and Electrochemistry