Chemical formula

A symbolic representation of a substance’s elemental composition, using element symbols and numbers to show which atoms are present and in what proportions or counts.

Chemical element: A pure substance defined by atoms with the same number of protons. Element symbols in formulas identify which kinds of atoms a substance contains.
Empirical formula: A chemical formula expressing the simplest whole-number ratio of atoms in a compound. It gives proportions but may not reveal the molecule’s actual atom counts.
Chemical equation: A symbolic statement showing the reactants and products of a chemical reaction. Formulas identify each substance in an equation and help balance atom counts.
Water: A compound whose molecules contain two hydrogen atoms bonded to one oxygen atom. H₂O illustrates how a molecular formula gives exact atom counts.
Chemical symbol: A one- or two-letter abbreviation representing a chemical element. Each element in a formula is written using its standardized symbol.
Molecular formula: A formula specifying the actual number of each type of atom in a molecule. Unlike a reduced ratio, it reports the molecule’s full elemental counts.
Stoichiometry: The quantitative study of relationships among reactants and products in chemical reactions. Formula subscripts determine the molar masses and atom ratios used in calculations.
Sodium chloride: An ionic compound composed of sodium and chloride ions in a one-to-one ratio. NaCl expresses the simplest ratio of ions rather than a discrete molecule’s atom count.
Subscript: A small number written below and to the right of a symbol, indicating how many units it represents. Subscripts specify atom counts or ratios within a formula.
Structural formula: A representation showing how atoms are connected or arranged in a molecule. It adds bonding information that an ordinary composition formula omits.

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