Glossary

Atom: The smallest particle of an element that can enter into a chemical combination.

Element: A substance composed of a single type of atom; cannot be decomposed by a chemical change.

Compound: A substance formed by the chemical combination of two or more elements in fixed proportions.

law of constant composition

(also, law of definite proportions) all samples of a pure compound contain the same elements in the same proportions by mass

law of definite proportions

(also, law of constant composition) all samples of a pure compound contain the same elements in the same proportions by mass

law of multiple proportions

when two elements react to form more than one compound, a fixed mass of one element will react with masses of the other element in a ratio of small whole numbers