The relative atomic mass, also known as atomic weight, is a measure that indicates the average mass of an atom of an element. It is expressed relative to the mass of carbon-12 (12C), which is assigned a value of exactly 12 atomic mass units (u).
The relative atomic mass takes into account the isotopic composition of an element, considering the different isotopes of the element and their respective abundances in nature. Isotopes are atoms of the same element with different numbers of neutrons in their nuclei, resulting in different atomic masses.
To calculate the relative atomic mass of an element, the atomic masses of all its naturally occurring isotopes are multiplied by their respective abundances and then summed. The resulting value is an average mass that reflects the weighted average of the masses of all isotopes present in a sample of the element.
The relative atomic mass is important in various scientific fields, including chemistry and physics, as it provides a standard for comparing the masses of different atoms and molecules. It is often used in chemical calculations, such as determining the molar mass of a substance or stoichiometric calculations in reactions.