Let's break down why:
* Elements: Elements are the simplest form of matter, meaning they cannot be broken down into simpler substances by chemical means. They are made up of only one type of atom. For example, gold (Au) is made up of only gold atoms.
* Compounds: Compounds are formed when two or more different elements chemically combine in a fixed ratio. This means the ratio of the different elements in a compound will always be the same. For example, water (H₂O) is always composed of two hydrogen atoms and one oxygen atom.
In contrast, mixtures are not considered pure substances because:
* Variable composition: Mixtures can have varying amounts of different substances.
* No chemical bonding: The components of a mixture are not chemically bonded together.
Therefore, elements and compounds are considered pure substances because they have a fixed and definite composition, which means they are made up of only one type of particle, be it an atom or a molecule.
