The terms "relative isotopic mass" and "relative atomic mass" are related but slightly different concepts in the field of atomic and molecular mass calculations. Here's a brief explanation of each term:
Relative Isotopic Mass: Relative isotopic mass refers to the mass of a particular isotope of an element relative to the mass of a carbon-12 (^12C) atom. It is denoted by the symbol "A" and is usually given as a whole number. For example, the relative isotopic mass of the carbon-12 isotope is defined as exactly 12 atomic mass units (u).
Relative Atomic Mass: Relative atomic mass, also known as atomic weight, is the weighted average mass of all naturally occurring isotopes of an element relative to the mass of a carbon-12 atom. It takes into account the relative abundance of each isotope in a naturally occurring sample. Relative atomic mass is denoted by the symbol "Ar" and is often reported as a decimal number. It is calculated by considering the masses and relative abundances of the isotopes.
To calculate the relative atomic mass, the relative isotopic masses of the isotopes are multiplied by their respective abundances and then summed. The formula is as follows:
Ar = (A1 × Abundance1) + (A2 × Abundance2) + ...
In this formula, A1, A2, etc., represent the relative isotopic masses of the isotopes, and Abundance1, Abundance2, etc., represent their respective abundances.
In summary, the relative isotopic mass refers to the mass of a specific isotope relative to the mass of carbon-12, while the relative atomic mass is the weighted average mass of all isotopes of an element taking into account their relative abundances.