Final answer:
A chemical formula shows the elements in a compound and the relative proportions of those elements. If only one atom of a specific type is present, no subscript is used. For atoms that have two or more of a specific type of atom present, a subscript is written after the symbol for that atom.
Step-by-step explanation:
A chemical formula is an expression that shows the elements in a compound and the relative proportions of those elements. If only one atom of a specific type is present, no subscript is used. For atoms that have two or more of a specific type of atom present, a subscript is written after the symbol for that atom. Molecular formulas do not indicate how the atoms are arranged in the molecule.