Here's why:

* Elements are the fundamental building blocks of matter. They cannot be broken down into simpler substances by chemical means.

* Compounds are formed when two or more elements chemically combine in a fixed ratio. This ratio is always the same for a given compound, regardless of the source or method of preparation.

For example:

* Water (H₂O) always contains two hydrogen atoms for every one oxygen atom.

* Sodium chloride (NaCl) always contains one sodium atom for every one chlorine atom.

This fixed ratio is what gives each compound its unique properties.