Memly's AP® Chemistry Core Concepts: 300 Study Cards

300 concepts, with 40 cards naming the misreading to avoid.

300 cards

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Front	Back
Atomic number and mass number	Definition: The atomic number is the proton count and fixes the element. The mass number is protons plus neutrons for one particular atom. Why it matters: Changing neutrons gives a different isotope of the same element, while changing protons gives a different element entirely.
Aufbau principle	Definition: Electrons fill the lowest available energy subshell first. Watch out: The 4s subshell fills before 3d, but once occupied the 3d electrons are lower in energy, which is why 4s electrons are removed first on ionization.
Effective nuclear charge	Definition: The net positive pull an outer electron feels, reduced from the full nuclear charge by shielding from inner electrons. Why it matters: It rises across a period and stays nearly constant down a group, which is the single idea most periodic trends rest on.
Ionic bonding	Definition: Electrostatic attraction between oppositely charged ions formed by electron transfer, typically between a metal and a nonmetal. Why it matters: The attraction extends in all directions through a lattice rather than between one pair, which is why ionic compounds have no molecules.
Lewis structure	Definition: A diagram showing bonding pairs and lone pairs, drawn so that the total valence electron count is conserved. Why it matters: The count comes first and the arrangement second, so a structure with the wrong total is wrong regardless of how reasonable it looks.
Trigonal planar geometry	Definition: Three electron domains arranged in a flat triangle. Angle: About 120 degrees. With one domain a lone pair, the molecular shape becomes bent.
Molecular orbital theory	Definition: A model in which atomic orbitals combine into orbitals belonging to the whole molecule. Why it matters: It explains properties the Lewis picture cannot, most obviously why oxygen is attracted into a magnetic field.
Intermolecular versus intramolecular forces	Definition: Intramolecular forces are the bonds within a molecule. Intermolecular forces act between separate molecules. Why it matters: Boiling breaks intermolecular forces only, which is why boiling points are far lower than bond energies and why a substance keeps its identity when it boils.
Boiling point and intermolecular forces	Definition: Boiling occurs when vapour pressure equals the external pressure, which requires enough energy to separate particles. Why it matters: Stronger intermolecular forces raise the boiling point, so comparing boiling points is a way of comparing those forces.
Like dissolves like	Definition: Substances dissolve best in solvents whose intermolecular forces resemble their own. Why it matters: Solution forms when solute-solvent attractions repay the energy of separating solute and solvent particles, so mismatched forces do not repay it.
The mole	Definition: The amount of substance containing a fixed number of particles, defined by the Avogadro constant. Why it matters: It links a countable number of particles to a mass that can be weighed, which is what makes stoichiometry possible.
Limiting reactant	Definition: The reactant that runs out first and therefore sets how much product can form. Why it matters: It is identified by comparing available moles against the mole ratio, not by comparing masses or by which is present in smaller amount.
Oxidation number rules	Definition: A bookkeeping charge assigned by convention, with elements at zero, monatomic ions at their charge, oxygen usually at minus two, and hydrogen usually at plus one. Watch out: Peroxides and metal hydrides break the usual oxygen and hydrogen assignments.
Kinetic molecular theory	Definition: Gas particles are in constant random motion, occupy negligible volume, exert no forces between collisions, and collide elastically, with average kinetic energy proportional to absolute temperature. Why it matters: Every gas law follows from these assumptions, so departures from ideal behaviour are departures from one of them.
Boyle's law	Definition: At constant temperature and amount, pressure and volume are inversely proportional. Why it matters: Halving the volume doubles the collision frequency with the walls, so the relationship follows from the model rather than being an empirical accident.
Dalton's law of partial pressures	Definition: The total pressure of a gas mixture is the sum of the pressures each gas would exert alone. Why it matters: It follows from particles not interacting, so each gas behaves as if the others were absent.
Reaction rate	Definition: The change in concentration of a reactant or product per unit time. Why it matters: Rate is defined as a positive quantity, so a reactant's rate of change carries a negative sign that is removed by convention.
Rate law	Definition: An equation giving rate as the rate constant times reactant concentrations each raised to an experimentally determined power. Watch out: The exponents come from experiment, not from the coefficients in the balanced equation, and the two agree only for an elementary step.
Catalyst	Definition: A substance that increases reaction rate by providing an alternative pathway with a lower energy barrier, and is not consumed overall. Watch out: It changes the rate in both directions equally and does not shift the position of equilibrium or change the overall energy released.
System and surroundings	Definition: The system is the part under study. The surroundings are everything else that can exchange energy with it. Why it matters: Signs are written from the system's point of view, so energy leaving the system is negative even though the surroundings gain it.
State function	Definition: A property depending only on the current state, not on how it was reached. Examples: Enthalpy, entropy, free energy, internal energy, temperature and pressure. Heat and work are not state functions. Why it matters: Path independence is what allows Hess's law to work at all.
Entropy as dispersal of energy	Definition: A measure of how many ways the energy of a system can be arranged among its particles. Why it matters: More available arrangements means higher entropy, which is why the idea is described as dispersal rather than simply disorder.
Dynamic equilibrium	Definition: A state in which forward and reverse reactions continue at equal rates, so concentrations no longer change. Watch out: Equal rates, not equal concentrations, and the reactions have not stopped.
Solubility product	Definition: The equilibrium constant for a slightly soluble ionic solid dissolving into its ions. Watch out: The solid does not appear in the expression, so the constant contains only the ion concentrations raised to their coefficients.
Arrhenius acid and base	Definition: An acid produces hydrogen ions in water and a base produces hydroxide ions. Why it matters: It is the narrowest of the three definitions, since it applies only in aqueous solution and only to substances containing those ions.
Autoionization of water	Definition: Water transfers a proton between its own molecules, producing small equal amounts of hydronium and hydroxide. Why it matters: It is why pure water conducts slightly and why hydroxide is present even in acidic solution.
Salt hydrolysis	Definition: Reaction of a salt's ions with water, producing an acidic or basic solution. Why it matters: The ions are conjugates of the acid and base that formed the salt, so their strengths determine the result.
Oxidation and reduction at electrodes	Definition: Oxidation is loss of electrons and reduction is gain, occurring at separate electrodes connected by a circuit. Why it matters: Separating the halves is what forces the electrons through an external path where their flow can be used.
Faraday constant	Definition: The electric charge carried by one mole of electrons. Why it matters: It converts between charge measured in the circuit and moles of electrons transferred, which is the link between electrical and chemical quantities.
Intensive and extensive properties in cells	Definition: Cell potential is intensive and does not change when a half reaction is multiplied. Free energy and charge are extensive and do. Why it matters: It is why balancing electrons changes the free energy calculation but never the potential.

About this deck

Most of this course is a small number of ideas asked in many disguises. Coulomb's law explains atomic radius, ionization energy, electronegativity and lattice energy. Le Chatelier explains solubility in acid, the common ion effect and why a catalyst changes nothing. A state function is why Hess's law works at all. Once you can name the underlying reason, an unfamiliar comparison becomes a question you have already answered in another form. So these 300 cards are built around the reason rather than the result. 298 open with a definition, 249 add why it matters, and 40 carry an explicit warning where the usual misreading is predictable: that weak describes ionization and not concentration, that a catalyst shifts nothing, that bond energies are averages, that a negative enthalpy change does not mean fast. The weighting is 36 cards on bonding and structure, 34 on acids and bases, 32 each on atomic structure, thermodynamics and equilibrium, 30 each on stoichiometry and kinetics, 28 each on intermolecular forces and electrochemistry, and 18 on gases. Element facts and ion formulas are not here. Symbols, atomic numbers and categories live in the Periodic Table Elements deck, and formulas and charges in the Polyatomic Ions deck, so the three fit together without repeating a card. Cards are tagged by topic and sub-topic, so you can drill just equilibrium, just the rate laws, or just the titration curves. Import it and the deck joins your spaced-repetition schedule, and what you should end up with is the ability to say not only what happens but which principle makes it happen.

Frequently asked

How does it fit with the Periodic Table and Polyatomic Ions decks?: They sit underneath it and share no cards. The Periodic Table deck gives each element its symbol, atomic number, category, group and period. The Polyatomic Ions deck gives formulas and charges. This deck is the reasoning built on top of those: why the radius trend runs the way it does, why a lattice energy is large, why a salt solution turns out acidic.
What is on each card?: A concept on the front. On the back, a definition on 298 of the 300, then on 249 the reason it matters, most often the principle a question would actually turn on. 40 cards add an explicit warning where the common misreading is predictable. Each line is labeled, so the back reads as a short structured answer rather than a paragraph.
Which topics get the most cards?: Bonding and structure 36, acids and bases 34, then atomic structure, thermodynamics and equilibrium at 32 each, stoichiometry and kinetics at 30 each, intermolecular forces and electrochemistry at 28 each, and gases 18. The weighting follows where the reasoning is hardest rather than where the content is longest to list.
Why are there no bond energy or reduction potential tables in it?: Because those values differ between sources and reference conditions, and an exam supplies them anyway. A card quoting one number would be wrong for anyone using a different table. So the cards teach what the quantity means and how the calculation is set up, including which direction to subtract in, and leave the numbers to whatever reference you are given.
How is it organized for studying one topic at a time?: Every card carries a topic tag and a finer sub-topic tag, across atomic structure, bonding, intermolecular forces, stoichiometry, gases, kinetics, thermodynamics, equilibrium, acids and bases, and electrochemistry. Filter by a tag to drill one topic, or by the finer tag for a single block such as rate laws, solubility equilibria or buffers and titration.
Can I import the whole deck on the free plan?: Yes. Importing a saved deck runs no new AI generation and spends no AI credits, so the free plan imports every card. You can study, edit and delete them afterwards.
Will importing it twice create duplicates?: No. Cards you already have are skipped and only cards added in a revision come through. Including re-imports after deleting it, one official deck can be imported three times per account.
Can I edit the cards after importing?: Yes. Once imported they are your cards: edit either side, delete the ones you already know cold, retag them, or move them into another deck.

AP® and Advanced Placement® are trademarks registered by the College Board, which is not affiliated with, and does not endorse, this deck. No official questions or course framework text are reproduced, and every card is written by Memly. Compiled 2026-08-22.