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 measurement of the solution's concentration

Answer: (C)

A chemical formula is a compact representation of a substance that shows which elements make it up and how many atoms of each element are present, using their chemical symbols. The exact numbers are shown with subscripts, or left implicit if there is one atom. For example, H2O tells us there are two hydrogen atoms and one oxygen atom in each molecule, and NaCl shows the ratio of sodium to chlorine. This makes formulas a precise snapshot of composition, not a description of color, not a method for naming compounds, and not a measure of concentration. Color describes a property, naming follows rules to give a substance its name, and concentration relates to how much solute is in a solution—things that are different from the actual composition expressed by a formula.