A chemical symbol is to an element as a chemical formula is to a **compound**.
A chemical symbol is a one- or two-letter designation of an element. For example, the symbol for oxygen is O. A chemical formula is a combination of chemical symbols that shows the elements in a compound and the relative proportions of those elements. For example, the chemical formula for water is H2O, which means that water is made up of two hydrogen atoms and one oxygen atom.
So, a chemical symbol is a short way of representing an element, while a chemical formula is a short way of representing a compound.