Atomic Mass and Isotopes

Vocabulary flashcards covering key definitions, formulas, and isotopic data regarding atomic mass calculations.

Atomic Mass

The weighted average of the masses of the naturally occurring mixture of isotopes of an element, expressed in atomic mass units ($\text{amu}$).

Atomic Mass Unit ($\text{amu}$)

A unit of mass defined as exactly $\frac{1}{12}$ the mass of a carbon-12 atom.

Carbon Isotope Abundance Table

A table detailing the isotopic mass and natural abundance for carbon-12 ($12.00000\,\text{amu}$ at $98.93\%$ abundance) and carbon-13 ($13.003355\,\text{amu}$ at $1.07\%$ abundance).

Formula for Atomic Mass

The formula used to calculate the weighted average mass of an element: $\text{atomic mass} = \sum (\text{fraction of isotope} \times \text{mass of isotope})$.

Mass Number ($A$)

The total number of protons and neutrons in an atom, which is distinct from atomic mass.

Copper-63

A naturally occurring isotope of copper with a mass of $62.9296\,\text{amu}$ and a natural abundance of $69.17\%$.

Copper-65

A naturally occurring isotope of copper with a mass of $64.9278\,\text{amu}$ and a natural abundance of $30.83\%$.

Bromine-79

A naturally occurring isotope of bromine with a mass of $78.918\,\text{amu}$ and a natural abundance of $50.69\%$.