Final answer:
Atoms are the basic building blocks of matter, elements are pure substances made up of only one type of atom, and compounds are substances composed of two or more elements chemically combined in definite proportions.
Step-by-step explanation:
Atoms are the basic building blocks of matter. They are the smallest unit of an element that still retains the chemical properties of that element. Elements are pure substances made up of only one type of atom. They are represented by symbols on the periodic table. Compounds are substances composed of two or more elements chemically combined in definite proportions. They can be broken down into simpler substances through chemical reactions.
Learn more about The relationship among atoms, elements, and compounds