They cannot be broken down into simpler entities by chemical or physical methods.
They have a fixed composition.
Example: Diamond, carbon dioxide.
A substance that only contains one type or class of atom is said to be an element. Since it cannot be altered through physical or chemical means to break down or create new substances, an element is a pure material. The majority of elements are metals, nonmetals, or metalloids.
Pure substances typically only include one type of atom or molecule and are homogeneous in nature.
Most of the time, the composition of these chemicals is constant or uniform.
The boiling and melting points of the substances are constant.
In a chemical reaction, a pure substance often takes part to produce predictable results.