Here's why:

* Elements are the simplest pure substances and are made up of only one type of atom. For example, gold (Au) is always made up of only gold atoms.

* Compounds are made up of two or more different elements chemically bonded together. Their chemical formulas can vary depending on the ratio of the elements. For example, water (H₂O) always has two hydrogen atoms and one oxygen atom, but glucose (C₆H₁₂O₆) has a different ratio of carbon, hydrogen, and oxygen.

Let me know if you'd like another riddle!