Aluminum is a substance because it is a particular type of matter that has specific and unique properties, It is element number 13 on the periodic table making it a "pure substance." It is impossible to separate Aluminium in two or more components; neither can Aluminium present different properties at different times; therefore it can be classified as a substance. Aluminum cannot be decomposed (separated by chemical methods) in two or more elemental substances or elements, which makes it an element as well.