What is a chemical formula?

• A. A description of the substance's color.
• B. A method for naming compounds.
• C. A representation of a substance using symbols for its constituent elements.
• D. A calculation of molecular weight.

Answer: (C)

A chemical formula is a concise representation of a substance that uses the symbols of the elements present and small numbers (subscripts) to show how many atoms of each element are in a molecule or formula unit. For example, water is H2O, indicating two hydrogen atoms and one oxygen atom. Sodium chloride is NaCl, with one sodium and one chlorine, and carbon dioxide is CO2, with one carbon and two oxygens. This is different from describing color, which is a property of the substance, or naming compounds, which is about giving them a name, or calculating molecular weight, which uses the formula to add up the masses of the atoms. The core idea is that the formula encodes the composition using element symbols and numbers.