How are atoms, molecules, and compounds related?
They are related in ways that they make up all sorts of matter.
Atoms most simply make up elements. A pure element will contain an atom of a single type, e.g: A pure piece of gold will contain only gold atoms, therefore it's chemically pure.
A molecule is two of the same atoms joined together chemically, most usually through covalent bonds. The halogens typically exist as diatomic molecules, e.g Chlorine goes around as
A compound is different types of elements chemically joined together. This is typically seen through ionic compounds that are joined through ionic bonds. Please note that a mixture and compound are not the same thing! Remember, a mixture is not chemically joined together.