An atom is the smallest particle of an element that has all the properties of the element. Note: The particles within an atom are called subatomic particles. Within the nucleus, there are two different kinds of subatomic particles - neutrons and protons - bound close together. A third kind of subatomic particle, called the electron, moves around the nucleus. Protons carry a positive charge, whereas electrons carry a negative charge. Neutrons have no charge.

A molecule is the smallest particle of a pure substance capable of independent existence. It exhibits all the properties of the substance. Note: Each molecule of an element is made up of identical atoms. Each molecule of a compound is made up of atoms of different elements that have been combined in a fixed proportion.

A symbol can be defined as the shorthand notation which represents an atom of an element. It normally consists of one or two letters from the Latin or English name of the element and is written with the first letter capitalised.