A molecule (pron.: //) is an electrically neutral group of two
or more atoms held together by covalent chemical bonds.
Molecules are distinguished from ions by their lack of
electrical charge. However, in quantum physics, organic
chemistry, and biochemistry, the term molecule is often used
less strictly, also being applied to polyatomic ions. In 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. A molecule
may be homonuclear, that is, it consists of atoms of a single
chemical element, as with oxygen (O2); or it may be a chemical
compound composed of more than one element, as with water (H2O).
Atoms and complexes connected by non-covalent bonds such as
hydrogen bonds or ionic bonds are generally not considered
single molecules. Molecules as components of matter are common
in organic substances (and therefore biochemistry). T