pure substance: is a phase of uniform composition and unchanging can not be decomposed into other substances of different classes by physical methods.
elements: they are pure substances that can not be decomposed into simpler ones through normal chemical processes.
compounds: they are pure substances made up of two or more elements, which can be decomposed by chemical methods on the elements of which are constituted. A compound always has the same elements and the same proportions regardless of the process followed.
Blended is an aggregation of different substances without causing any chemical reaction between them and therefore may be separated by physical methods.
ponderal laws: they refer to the quantity of matter of different substances involved in chemical combination.
mole is the amount of substance containing the same number of elementary entities which are in 0.012 kg of carbon 12.