What are the rules to writing formulas?

When writing chemical formulas, the following rules should be followed: First, use the correct symbols for each element, with the first letter capitalized and any subsequent letters in lowercase. Second, indicate the number of atoms of each element using subscripts; if there is only one atom, no subscript is needed. Third, for compounds with polyatomic ions, use parentheses to group the ions and indicate the quantity with a subscript outside the parentheses if necessary. Lastly, for ionic compounds, the formula should reflect the overall charge balance between the positive and negative ions.