AP Chem Terms

Atom

A basic unit of matter that consists of a dense nucleus surrounded by electrons.

Isotope

Atoms of the same element with different numbers of neutrons.

Ion

An atom or molecule with a net electric charge due to the loss or gain of electrons.

Mole

A quantity equal to 6.022 x 10²³ particles (Avogadro’s number).

Molar Mass

The mass of one mole of a substance, measured in grams per mole (g/mol).

Empirical Formula

The simplest whole-number ratio of atoms in a compound.

Molecular Formula

The actual number of atoms of each element in a molecule.

Percent Composition

The percentage by mass of each element in a compound.

Stoichiometry

The calculation of reactants and products in chemical reactions.

Limiting Reactant

The substance that is completely used up in a reaction, limiting the amount of product formed.

Theoretical Yield

The maximum amount of product that could be formed from given reactants.

Actual Yield

The amount of product actually obtained from a chemical reaction.

Percent Yield

The ratio of actual yield to theoretical yield multiplied by 100.

Electronegativity

The ability of an atom to attract electrons in a chemical bond.

Ionization Energy

The energy required to remove an electron from a gaseous atom or ion.

Electron Affinity

The energy change when an electron is added to a neutral atom.

Atomic Radius

The distance from the nucleus to the outermost electron.

Ionic Bond

A bond formed by the electrostatic attraction between oppositely charged ions.

Covalent Bond

A bond formed when two atoms share electrons.

Metallic Bond

A bond formed by the attraction between positively charged metal ions and the electrons around them.

Intermolecular Forces

Forces of attraction between molecules (e.g., hydrogen bonding, dipole-dipole, London dispersion).

Hydrogen Bond

A strong type of dipole-dipole interaction between molecules containing H and N, O, or F.

Dipole-Dipole Force

Attractive forces between polar molecules.

London Dispersion Force

Weak intermolecular forces from temporary shifts in electron density.

Chemical Reaction

A process in which substances are changed into different substances.

Net Ionic Equation

An equation that shows only the species that actually participate in the reaction.

Precipitate

A solid that forms and settles out of a liquid mixture.

Acid

A substance that increases the H⁺ concentration in solution.

Base

A substance that increases the OH⁻ concentration in solution.

Strong Acid

An acid that completely dissociates in solution.

Weak Acid

An acid that partially dissociates in solution.

Strong Base

A base that completely dissociates in solution.

Weak Base

A base that partially dissociates in solution.

pH

A measure of the hydrogen ion concentration of a solution.

Buffer

A solution that resists changes in pH when an acid or base is added.

Titration

A method to determine the concentration of a substance using a solution of known concentration.

Equivalence Point

The point in titration where the amount of acid equals the amount of base.

End Point

The point at which the indicator changes color in a titration.

Kinetics

The study of the rate of chemical reactions.

Activation Energy

The minimum energy needed for a reaction to occur.

Catalyst

A substance that increases the rate of a reaction by lowering the activation energy.

Rate Law

An equation that relates the rate of a reaction to the concentration of reactants.

Reaction Mechanism

The step-by-step sequence of elementary reactions by which a chemical change occurs.

Intermediate

A species that appears in some steps of a reaction mechanism but not in the overall reaction.

Equilibrium

A state where the forward and reverse reactions occur at the same rate.

Le Chatelier’s Principle

If a system at equilibrium is disturbed, it will shift to counteract the disturbance.

Equilibrium Constant (K)

The ratio of product concentrations to reactant concentrations at equilibrium.

Solubility

The amount of a substance that dissolves in a given volume of solvent.

Saturated Solution

A solution containing the maximum amount of dissolved solute.

Unsaturated Solution

A solution that can dissolve more solute.

Supersaturated Solution

A solution that contains more solute than it can theoretically hold at a given temperature.

Solubility Product Constant (Ksp)

An equilibrium constant for the dissolution of a slightly soluble compound.

Thermodynamics

The study of energy changes in chemical processes.

Enthalpy (ΔH)

The heat content of a system at constant pressure.

Entropy (ΔS)

A measure of disorder or randomness in a system.

Gibbs Free Energy (ΔG)

The energy associated with a chemical reaction that can be used to do work.

Spontaneous Process

A process that occurs without outside energy input.

Endothermic Process

A process that absorbs heat from the surroundings.

Exothermic Process

A process that releases heat to the surroundings.

Oxidation

The loss of electrons.

Reduction

The gain of electrons.

Oxidizing Agent

The substance that causes oxidation by accepting electrons.

Reducing Agent

The substance that causes reduction by donating electrons.

Redox Reaction

A chemical reaction involving the transfer of electrons.

Electrochemistry

The study of chemical processes that cause electrons to move.

Voltaic (Galvanic) Cell

A device that uses a spontaneous redox reaction to generate electrical energy.

Electrolytic Cell

A device that uses electrical energy to drive a non-spontaneous chemical reaction.

Standard Reduction Potential

The tendency of a species to gain electrons under standard conditions.

Half-Cell

One part of a redox reaction where oxidation or reduction occurs.

Salt Bridge

A pathway that allows the flow of ions to maintain electrical neutrality in a voltaic cell.