A material that has the same composition and properties throughout is a pure chemical substance. A chemical substance cannot be separated into components by a physical method. Chemical substances can be plasma, gases, liquids or solids. Examples of pure substances include sodium chloride, sodium bicarbonate and sucrose.
Every pure element and every pure compound are considered to be substances. Iron is an element and therefore it is a substance. A substance does not have to consist of a single element or molecule type. A substance is something that is free from contamination. Another example of a substance is methane, it is a pure compound and, therefore, a substance.