Atoms, Particles and Molecules

Atoms are the smallest pieces of matter; they are made of particles (protons and electrons). When atoms are grouped together, the groups are called molecules, which are the smallest bits of compounds.

By way of example, within the element copper, a copper atom is the smallest piece of copper that exists. Hydrogen is an element; two hydrogen atoms and one oxygen atom combine to form a molecule of water, which is a compound.

Element - a basic substance that can't be simplified, such as copper
Atom - the smallest amount of an element, such as copper atom
Molecule - two or more atoms that are chemically joined together, such as hydrogen or oxygen
Compound - a molecule that contains more than one element, such as water