A chemical formula is a standardized notation used to represent the chemical composition of a substance, indicating the types and relative numbers of atoms present in a molecule or ionic compound. These formulas utilize the elemental symbols derived from the periodic table, with numerical subscripts specifying the exact ratio of atoms of each element. They are fundamental tools in chemistry, allowing scientists to predict stoichiometry, understand molecular weight, and describe the structural makeup of matter. The distinction between empirical formulas, which convey the simplest whole-number ratio of atoms, and molecular formulas, which state the actual count of atoms, is crucial for fully characterizing chemical compounds.