Atom
The basic unit of matter.
Element
A pure substance consisting of only one type of atom.
Molecule
A group of atoms bonded together.
Compound
A substance composed of different elements in fixed ratios.
Explain the statement ‘‘All molecules are compounds but not all compounds are molecules’’
Molecules are bonded atoms, while compounds are different element substances. Some compounds, like salts, consist of ions. Molecules are a subset of compounds.