molecule definition
A molecule may be homonuclear, that is, it consists of atoms of a single chemical element, as with oxygen (O 2); or it may be heteronuclear, a chemical compound composed of more than one element, as with water (H 2 O).n the kinetic theory of gases, the term molecule is often used for any gaseous particle regardless of its composition. According to this definition, noble gas atoms are considered molecules despite being composed of a single non-bonded atom.