Answer:
Pure substances can be divided into two groups: elements and compounds.
Explanation:
Pure substances can be recognized because they have a definite constant composition, as can be seen in the formula, and distinct chemical properties.
For example, H₂O is a pure substance where the relation of 2 atoms of Hydrogen to 1 atom of Oxygen is always true. O₂ is also a pure substance because 1 molecule of O₂ always contains two atoms of Oxygen.
As we can see from above, pure substances can be formed by one or more types of atoms. Substances formed by 2 or more types of atoms are known as compounds (e.g. H₂O, CO₂). Substances formed by 1 type of atoms are known as elements (e.g. Na, O₂, O₃).
Compounds and elements are kinds of pure substances, so they inherit all properties from them (definite constant composition, distinct chemical properties).
