Chemistry Explorer
Search and explore 92 chemistry concepts
Browse 92 chemistry concepts covering the structure of matter, chemical reactions, stoichiometry, and material properties. Each concept provides a clear definition, an intuitive explanation of the underlying idea, common mistakes students make, and links to prerequisite knowledge — helping you see how ideas like moles, bonding, and equilibrium connect.
Mole
A 'chemist's dozen'—a huge number that makes atom-counting practical.
Avogadro's Number
A mind-bogglingly large number — but it's exactly the right size to make atomic counting practical.
Molar Mass
How much one mole weighs. For elements, it's the number on the periodic table.
Stoichiometry
Using the recipe (balanced equation) to figure out how much of each ingredient you need.
Limiting Reactant
If you have 10 buns and 5 patties, you can only make 5 burgers—patties are limiting.
Theoretical Yield
The perfect-world result — the most product you could possibly get if nothing is lost or wasted.
Percent Yield
How much of the possible product you actually got — 100% is perfect, real reactions are always less.
Concentration
How 'strong' a solution is—more solute in the same volume = more concentrated.
Solution
One substance completely mixed into another—you can't see separate parts.
Solubility
How much can dissolve before no more will. Sugar: high solubility. Sand: zero.
Dilution
Watering down a drink—same amount of flavor, more liquid, weaker taste.
Empirical Formula
The reduced fraction of atoms—smallest numbers that show the ratio.
Molecular Formula
The real count of atoms, not just the ratio — it tells you exactly what the molecule contains.
Percent Composition
What fraction of the compound's total weight is made up by each element inside it.
Gas Laws
How gases behave when you squeeze them, heat them, or add more.
Atomic Mass
The number under each element on the periodic table—a weighted average of all its isotopes.
Grams (Mass)
Grams tell you how heavy something is. A paperclip is about 1 gram. Moles tell you how many particles you have—a completely different question.
Titration
Slowly adding a known solution to an unknown one until the reaction is just complete — the volume used reveals the concentration.
Atom
The tiny building blocks everything is made of. Break matter down far enough, you get atoms.
Element
A pure substance that can't be broken down chemically. Gold is gold, oxygen is oxygen.
Proton
The identity badge of an atom—how many protons determines what element it is.
Neutron
The glue that helps hold the nucleus together without adding charge.
Electron
The particles that do the 'dancing'—they're what's involved in bonding and reactions.
Atomic Number
The atom's ID number — $Z = 6$ always means carbon, no matter what else changes.
Mass Number
How heavy the nucleus is — each proton and neutron contributes about 1 atomic mass unit.
Isotope
Same element, slightly different weight. Chemically identical, but different mass.
Electron Shell
Electrons live in 'floors' around the nucleus. Lower floors fill first.
Valence Electron
The electrons that 'reach out' to other atoms. These do the bonding.
Periodic Table
A map of all elements organized so similar ones are in the same column.
Ion
An atom that's not neutral—it has more or fewer electrons than protons.
Molecule
Atoms stuck together. Water ($\text{H}_2\text{O}$) is one molecule with 3 atoms.
Compound
Elements joined together to make something new with different properties.
Mixture
Things stirred together but not joined. Each substance keeps its own properties.
Chemical Bond
The 'glue' that holds atoms together, made by sharing or transferring electrons.
Ionic Bond
One atom gives electrons away; another takes them. Opposites attract.
Covalent Bond
Atoms hold electrons together like kids sharing a toy. Neither gives it away.
Octet Rule
8 is the magic number. Atoms 'want' a full outer shell like noble gases.
Lewis Structure
A map showing how electrons are arranged and shared between atoms.
Electronegativity
How 'greedy' an atom is for electrons. Fluorine is most greedy.
Electron Configuration
Electrons fill energy levels like seats in a theatre — front rows first, then moving back.
Molecular Geometry
Electron pairs repel each other, pushing atoms as far apart as possible — this determines the molecule's shape.
Polar Covalent Bond
Two atoms sharing electrons, but one pulls harder — like a tug of war where one side is stronger.
Radioactivity
Some nuclei are unstable and shed particles to reach a more stable state — like a unstable pile of blocks rearranging.
Molecular Polarity
Even if individual bonds are polar, the molecule can be nonpolar if the dipoles cancel out symmetrically.
Matter
Everything you can touch, see, or weigh is matter. Air is matter too — you just can't see it.
Physical Property
Properties you can detect just by looking, touching, or measuring — without turning the substance into something else.
Chemical Property
Properties you can only discover by trying to react the substance — they describe what it can become, not what it looks like.
State of Matter
Particles packed tight and vibrating = solid. Particles sliding past each other = liquid. Particles flying freely = gas.
Phase Change
Add enough heat and a solid melts to liquid, then boils to gas. Remove heat and the reverse happens.
Particle Theory
Everything is made of tiny particles that are always moving. How fast they move and how tightly they're held together explains solids, liquids, and gases.
Density
Density answers 'how heavy is this for its size?' A small lead ball is heavier than a large foam ball — lead is denser.
Pure Substance
Every particle in a pure substance is the same. Pure water is all H₂O — no exceptions.
Mechanical Mixture
You can see the different parts. A salad, trail mix, or sand in water — the ingredients don't blend together evenly.
Homogeneous Mixture
It looks the same everywhere. You can't see the separate parts, even under a microscope.
Heterogeneous Mixture
Different parts look or behave differently. One spoonful is not the same as another.
Solute
The thing that 'disappears' when you dissolve it — like sugar dissolving in tea. The sugar is the solute.
Solvent
The 'background' substance that the solute dissolves into. Water is called the 'universal solvent' because it dissolves so many things.
Mixture Separation
Different substances have different properties — use those differences to pull them apart. Heavy things sink, liquids evaporate at different temperatures.
Synthesis Reaction
Building something bigger from smaller parts — like assembling LEGO bricks into a structure.
Decomposition Reaction
The reverse of synthesis — taking apart a complex structure into simpler pieces.
Single Displacement
A bully element kicks a weaker one out of its compound — like a stronger player replacing a weaker one on a team.
Double Displacement
Two couples swap partners at a dance — each positive ion pairs with the other's negative ion.
Combustion
Burning. When something burns, it's reacting with oxygen and releasing energy as heat and light.
Precipitation Reaction
Mix two clear solutions and a solid appears 'out of nowhere' — the ions combine to form a compound that won't dissolve.
Net Ionic Equation
Strip away the bystanders. Some ions just float around doing nothing — the net ionic equation shows only the ones that actually react.
Oxidation Number
An imaginary 'electron bookkeeping' system. If an atom 'owns' more electrons than usual, its oxidation number is negative; fewer means positive.
Formula Writing
Chemical formulas are the 'spelling' of chemistry — they tell you exactly which atoms and how many of each are in a compound.
Nomenclature
Chemistry has a naming system so that every compound gets exactly one name and every name points to exactly one compound — like a universal address system.
Chemical Reaction
Old bonds break, new bonds form. You end up with different stuff than you started with.
Reactant
What you start with — the ingredients that get used up to make something new.
Product
What you end up with after the reaction — the new stuff that gets made from the ingredients.
Chemical Equation
A recipe that shows what goes in, what comes out, and in what amounts.
Balancing Equations
Atoms can't appear or disappear — every atom on the left must show up on the right.
Conservation of Mass
Matter can't vanish or appear from nothing. What goes in equals what comes out.
Exothermic Reaction
The reaction gives off heat—you can feel the surroundings get warmer as it proceeds.
Endothermic Reaction
The reaction needs heat to proceed — you can feel the surroundings get colder as it runs.
Activation Energy
The 'hill' reactants must climb over before the reaction can proceed.
Catalyst
A helper that makes the reaction easier but isn't used up in the process.
Reaction Rate
How quickly the reaction happens—from instant explosion to years of rusting.
Collision Theory
Molecules must hit each other the right way and hard enough for bonds to break.
Chemical Equilibrium
The reaction is still happening both ways, but the amounts stay constant.
Le Chatelier's Principle
Push on equilibrium, and it pushes back. Add something, and the system uses it up.
Acid
Sour-tasting substances that can 'burn'—they give away hydrogen ions.
Base
Slippery substances that can neutralize acids—they remove hydrogen ions.
pH
A number that tells you: acid (low), neutral (7), base (high).
Neutralization
Acid + Base → they cancel each other out, making water and salt.
Oxidation
Giving away electrons. Originally meant 'gaining oxygen' but it's broader.
Reduction
Grabbing electrons. The charge gets 'reduced' (becomes more negative).
Redox Reaction
One thing loses electrons (oxidized), another gains them (reduced).
Electrolyte
Salt dissolved in water breaks into charged particles (ions) that carry electric current.
Equilibrium Constant
A large K means products are favored; a small K means reactants are favored.
Enthalpy
Enthalpy change tells you how much heat a reaction releases or absorbs.