Glossary
matter
Matter is anything with mass that takes up space, and it exists as a solid, a liquid, a gas or a plasma.
Matter is anything that has mass and takes up space — the substance everything physical is made of. It is described in three common states. A solid holds its own shape because its particles are packed and locked in place; a liquid keeps its volume but takes the shape of its container because its particles slide past each other; a gas fills its container because its particles are far apart and move freely. The state is not a property of the substance forever — it depends on how much energy the particles have and how strongly they pull on each other, which is why water is ice, water or steam at different temperatures. A fourth state, plasma, is a gas whose electrons have been stripped away, and it is what a flame and a lightning bolt are made of. Questions about matter usually ask which state a description fits, or whether a change altered the substance or only its form.
Taught in
Related terms
- physical change — A physical change alters a substance's form, size or state without making a new substance — melting, cutting and dissolving are the usual examples.
- chemical change — A chemical change makes a new substance with new properties — burning, rusting and digesting food are chemical changes.
- hydrogen bond — A hydrogen bond is a weak attraction between a hydrogen already bonded to oxygen, nitrogen or fluorine and a nearby lone pair on another molecule, or on another part of the same molecule.
- specific heat — Specific heat is the energy needed to raise one gram of a substance by one degree Celsius, in J/(g·°C); water's 4.18 is high, so it resists a temperature change.
Source: NIST periodic table and reference data for the atomic masses and half-life figures, NIH PubChem for the substance data, and NIST Special Publication 811 for the unit conventions — the same sources the chemistry guide cites. All three are US federal government material, not subject to copyright in the United States. Every definition, example and calculation above was written for this course; no dictionary or textbook text is reproduced. (NIST and PubChem accessed 2026-10-26; definitions written 2026-10-27)