In a chemical formula, the cation (positively charged ion) is written first.

Here's why:

* Ions: Chemical formulas represent the composition of ionic compounds, which are formed by the electrostatic attraction between oppositely charged ions.

* Cation and Anion: The positively charged ion is called the cation, and the negatively charged ion is called the anion.

* Convention: By convention, the cation is always written first in the chemical formula.

For example, in the formula for sodium chloride (NaCl), sodium (Na+) is the cation and chlorine (Cl-) is the anion.