Chemistry Concepts
Understand the composition and behavior of matter. From atomic structure to chemical reactions, build intuition for the molecular world.
Explore by Topic Area
Structure of Matter
Atoms, elements, compounds, bonding, molecular structure
26 concepts
Chemical Change
Reactions, equilibrium, kinetics, thermochemistry
24 concepts
Quantity & Proportion
Moles, stoichiometry, concentration, gas laws
18 concepts
Matter & Mixtures
States of matter, properties, mixtures, separation
14 concepts
Reaction Patterns
Synthesis, decomposition, displacement, combustion
10 concepts
Popular Concepts
Atom
The smallest unit of an element that retains the chemical properties of that element.
Element
A pure substance made entirely of one type of atom, uniquely defined by its number of protons.
Compound
A pure substance made of two or more different elements chemically bonded in fixed proportions.
Chemical Bond
A force of attraction between atoms that holds them together in molecules or compounds, formed by sharing or transferring electrons.
Mole
A counting unit for atoms and molecules, equal to $6.022 \times 10^{23}$ particles (atoms, molecules, or ions).
Chemical Reaction
A process where substances (reactants) are transformed into different substances (products).
Acid
A substance that donates $\text{H}^+$ ions (protons) when dissolved in water, lowering the pH.
Base
A substance that accepts $\text{H}^+$ ions or donates $\text{OH}^-$ ions in solution, raising pH.
Density
The mass of a substance per unit volume. A measure of how tightly packed the particles are.
Combustion
A rapid exothermic reaction between a fuel and oxygen, producing carbon dioxide and water (for hydrocarbon fuels).
Stoichiometry
The branch of chemistry that calculates the quantities of reactants and products in chemical reactions.
State of Matter
The form matter takes depending on the arrangement and movement of its particles: solid, liquid, or gas (plus plasma).
Core Themes
Structure Determines Properties
How atoms are arranged determines how substances behave. Structure is destiny.
Conservation of Matter
Atoms rearrange in reactions but are never created or destroyed. Matter is conserved.
Energy Drives Change
Chemical reactions involve energy transfer. Stability and reactivity are about energy.
Chemistry Guides
In-depth guides that consolidate related chemistry concepts with definitions, examples, and common mistakes.
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Start with atomic structure—the foundation of chemistry—or dive into any topic.