sentence: Atoms are made up of protons, neutrons, and electrons.
sentences_before: A 'chemical element' is a substance that contains only one type of atom. An element is the smallest amount of a substance can still keep its properties. If a substance contains more than one type of atom, it is a compound. An element can be a solid, liquid or gas. The smallest particle of such an element is an atom.
concept_name: atom
headings: Chemical element
categories: Nuclear physics