How is relative isotopic mass expressed?

Relative isotopic mass is expressed on a scale where carbon-12 is defined as exactly 12 units. This means that other isotopes are measured in comparison to carbon-12. By using this scale, scientists can report the mass of different isotopes in a consistent manner, allowing for meaningful comparisons between them.

This system is incredibly useful because it standardizes measurements of atomic masses across the periodic table, facilitating calculations in various areas of chemistry, including stoichiometry and molecular weight determinations. The relative isotopic mass indicates how much heavier or lighter an isotope is compared to carbon-12, forming a foundational aspect of understanding atomic structure and behavior in chemical reactions.