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AP Chemistry

From counting atoms by weighing them to the voltage a battery can give: the AP Chemistry curriculum: structure and bonding, reactions and their rates, equilibrium, acids and bases, and the thermodynamics that decides what happens, told as one connected story.

9 units · 45 chapters

Start with chapter 1

01

Atomic Structure and Properties

4 chapters
  1. 01Counting Atoms by Weighing: Moles, Molar Mass, and Mass SpectraA gram of hydrogen holds more atoms than there are grains of sand on Earth, yet a balance counts them for you. The trick is knowing exactly how much one atom weighs, and a mass spectrometer tells you.
  2. 02What Is It Made Of: Empirical Formulas and the Composition of MixturesBurn a sample, weigh the carbon dioxide and water that come off, and you can name the compound you started with. The same arithmetic tells you how pure a sample is.
  3. 03Where the Electrons Are: Configurations and Photoelectron SpectroscopyNobody has seen an electron shell, yet a photoelectron spectrum shows them as cleanly as rungs on a ladder. Knock electrons out with light and count how much energy each one cost.
  4. 04Reading the Periodic Table: Trends, Valence Electrons, and IonsThe periodic table is not a list; it is a map of how hard each atom holds its outer electrons. Read the map and you can predict which elements grab electrons, which give them up, and what ions they form.
02

Compound Structure and Properties

4 chapters
  1. 05Types of Bonds and the Energy of Holding Atoms TogetherSalt shatters, wax bends, copper conducts, and all three are just atoms holding hands in different ways. Pull two atoms apart on an energy graph and the bond's length and strength both appear.
  2. 06Ionic Solids, Metals, and Alloys: How Solids Are BuiltWhy does a copper wire bend where a salt crystal cracks, and why does adding a little carbon turn soft iron into steel? Draw the particles and the answers are already in the picture.
  3. 07Lewis Diagrams, Resonance, and Formal ChargeOzone's two bonds should be different lengths if either Lewis diagram were true, and they are exactly equal. The molecule is not flipping between pictures; the picture was never complete.
  4. 08The Shapes of Molecules: VSEPR, Hybridization, and PolarityWater bends, carbon dioxide is straight, and that one difference is why one is a greenhouse gas and the other is what falls from the sky. Electron pairs push each other apart, and the shape follows.In preparation
03

Properties of Substances and Mixtures

6 chapters
  1. 09Intermolecular Forces: Why Molecules Stick TogetherHelium boils four degrees above absolute zero and water boils at a hundred, yet both are tiny neutral particles. Everything about a liquid is decided by forces far weaker than a bond.In preparation
  2. 10Solids, Liquids, and Gases: Properties from ParticlesDiamond and graphite are both pure carbon, yet one cuts glass and the other writes on paper. The difference is entirely in how the particles are held, and the same idea explains every solid, liquid, and gas.In preparation
  3. 11The Ideal Gas Law, Kinetic Molecular Theory, and Real GasesA gas has no idea what its molecules are made of; at ordinary pressures a liter of any gas holds the same number of particles. Then squeeze it hard or chill it, and the molecules start to matter.In preparation
  4. 12Solutions and Molarity: Picturing What Is DissolvedA teaspoon of salt in a glass of water and the same teaspoon in a swimming pool are both salt water, and no one would confuse them. Concentration is the number that keeps them apart.In preparation
  5. 13Separating Mixtures and Why Things DissolveInk is one color on the pen and five colors on a wet paper towel. Every separation, from that towel to an oil refinery, is a competition between attractions, and the same competition decides what dissolves.In preparation
  6. 14Light as a Probe: Spectroscopy, Photons, and the Beer–Lambert LawA microwave oven, a heat lamp, and a sunburn are the same physics at three energies: light making molecules spin, vibrate, or rearrange their electrons. Shine light through a solution and it even counts the molecules for you.In preparation
04

Chemical Reactions

5 chapters
  1. 15Writing What Happened: Evidence, Balanced Equations, and Net Ionic EquationsMix two clear solutions and a white solid appears from nowhere. Nothing was created; atoms only changed partners, and a balanced equation is the receipt that proves it.In preparation
  2. 16Physical Change, Chemical Change, and the Three Kinds of ReactionDissolving salt breaks every bond in the crystal, so is it a chemical change? The honest answer is that the line is drawn by what breaks and what forms, and the same question sorts every reaction into three families.In preparation
  3. 17Stoichiometry and Titration: How Much ReactsA recipe with two eggs per cake makes only as many cakes as the eggs allow, however much flour is on the shelf. A balanced equation is a recipe, and a titration runs it backward.In preparation
  4. 18Brønsted–Lowry Acids and Bases: Proton TransferWater is an acid, water is a base, and water is neither, all at once and all correct. Acidity is not a property of a substance but a transaction between two of them.In preparation
  5. 19Redox Reactions and Balancing with Half-ReactionsIron rusts, batteries die, and a match burns for the same reason: electrons changed owners. Split any such reaction into the half that gives and the half that takes, and balancing becomes bookkeeping.In preparation
05

Kinetics

5 chapters
  1. 20Reaction Rates and the Rate LawDouble the amount of one reactant and a reaction may go twice as fast, four times as fast, or not change at all. The exponent is a fact about the reaction, and only an experiment can reveal it.In preparation
  2. 21Concentration Over Time: Integrated Rate Laws and Half-LifeA first-order reaction loses half of what is left in the same time, every time, whether it starts with a ton or a gram. Plot the data three ways and the reaction picks the straight line itself.In preparation
  3. 22Collisions, Elementary Steps, and the Energy ProfileMolecules in a flask collide billions of times a second, and almost every collision does nothing. A reaction happens only when two of them hit hard enough and the right way round.In preparation
  4. 23Reaction Mechanisms: From Steps to the Rate LawA balanced equation says what went in and what came out, never how. The rate law is a fingerprint of the slowest step, and it can rule a proposed mechanism in or out.In preparation
  5. 24Multistep Energy Profiles and CatalysisA catalyst is used up in one step and handed back in another, so it never appears in the final equation and never runs out. It does not push the reaction; it digs a lower pass through the mountain.In preparation
06

Thermochemistry

4 chapters
  1. 25Endothermic, Exothermic, and How Heat Actually MovesAn instant cold pack gets cold with nothing plugged in, and a hand warmer gets hot the same way. Energy did not appear or vanish; it moved between the chemicals and the surroundings, one collision at a time.In preparation
  2. 26Calorimetry and the Energy of Phase ChangesWater at a rolling boil never gets hotter than 100 degrees no matter how high the flame; every joule goes into pulling molecules apart. A thermometer in a styrofoam cup can measure that.In preparation
  3. 27Enthalpy of Reaction and Bond EnthalpiesBreaking bonds always costs energy and forming them always pays; a flame is just a reaction that forms stronger bonds than it breaks. Tally the bonds and you can estimate the heat before striking the match.In preparation
  4. 28Enthalpies of Formation and Hess's LawSome reactions cannot be run in a calorimeter, yet their heat is known to four figures. Heat changes add like stair steps, so a measurable route reaches the same landing.In preparation
07

Equilibrium

6 chapters
  1. 29Dynamic Equilibrium: When Nothing Seems to ChangeSeal water in a jar and the level stops falling, yet molecules are still leaving the surface every instant. Nothing has stopped; two opposite processes have simply reached the same speed.In preparation
  2. 30The Reaction Quotient and the Equilibrium ConstantAt equilibrium the concentrations can be anything, but one particular ratio of them is always the same number for a given reaction and temperature. That number is a property of the reaction itself.In preparation
  3. 31What the Size of K Tells You, and How K Values CombineA K of a billion and a K of a billionth describe the same kind of equilibrium, one that lies almost entirely on one side. Reverse the reaction, double it, or chain it to another, and K follows simple rules.In preparation
  4. 32Equilibrium Calculations and Particle PicturesGiven a starting mixture and K, the equilibrium amounts are fixed before the reaction begins. An initial-change-equilibrium table finds them, and a drawing of the particles checks the answer.In preparation
  5. 33Le Châtelier's Principle and the Reaction QuotientAdd product to an equilibrium mixture and the reaction runs backward until the same ratio is restored, as if it remembered the number. It does not remember anything; Q simply no longer equals K.In preparation
  6. 34Solubility Equilibria and the Common-Ion EffectSilver chloride barely dissolves in water, and it dissolves even less in salt water. The salt supplies chloride, and an equilibrium that already has product has nowhere to go.In preparation
08

Acids and Bases

6 chapters
  1. 35Water, pH, and Strong Acids and BasesPure water is a very weak acid and a very weak base reacting with itself, one molecule in half a billion at a time. That tiny equilibrium is the ruler every acid and base is measured against.In preparation
  2. 36Weak Acid and Weak Base EquilibriaVinegar is mostly intact acetic acid molecules with only one in a hundred giving up its proton. The pH of a weak acid is an equilibrium problem, and K_a is its equilibrium constant.In preparation
  3. 37Acid–Base Reactions and Titration CurvesDrip base into a weak acid and the pH creeps, then leaps, then creeps again; the whole story of the solution is drawn in that curve. Halfway to the leap, the curve reads off the acid's pK_a for free.In preparation
  4. 38Structure, Strength, and the Meaning of pK_aHydrochloric acid and acetic acid both hold one proton, and one lets go a million times more readily. The difference is written in their structures, and pK_a is the number that reads it.In preparation
  5. 39Buffers: Resisting pH ChangeYour blood is hit with acid every time you exercise, and its pH moves by a few hundredths. A solution holding both members of a conjugate pair absorbs acid and base alike, up to a limit.In preparation
  6. 40pH and SolubilityTooth enamel survives water for a lifetime and dissolves in a soft drink in hours. When one of a salt's ions is a weak base, acid pulls it out of solution and the salt follows.In preparation
09

Thermodynamics and Electrochemistry

5 chapters
  1. 41Entropy: How Matter and Energy Spread OutIce melts in a warm room without anyone pushing it, and a gas fills a vacuum on its own. Both are the universe drifting toward the arrangements that can happen the most ways.In preparation
  2. 42Gibbs Free Energy, Thermodynamic Favorability, and Kinetic ControlDiamond should turn into graphite and every log should burst into flame, thermodynamically speaking. Free energy tells you the direction nature prefers; it says nothing about how long the wait is.In preparation
  3. 43Free Energy, Equilibrium, Dissolution, and Coupled ReactionsA cell builds proteins by running reactions that should not run, and it pays for each one with a reaction that runs downhill. Free energies add, so a favorable step can carry an unfavorable one.In preparation
  4. 44Galvanic and Electrolytic Cells: Voltage from Free EnergySeparate the two halves of a redox reaction and force the electrons through a wire, and a reaction becomes a battery. The voltage on the meter is the free energy change in different units.In preparation
  5. 45Cells Away from Standard Conditions, and ElectrolysisA battery's voltage sags as it runs down because the reaction is creeping toward equilibrium, where the voltage is exactly zero. Push current the other way and you can run the reaction uphill, one mole of electrons at a time.In preparation
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