Final answer:
The relative atomic mass of an element is the weighted average of its isotopes' masses, considering their relative abundances, and is measured in atomic mass units. This value is listed on the periodic table under the element's symbol.
Step-by-step explanation:
The relative atomic mass of an element is a weighted average that reflects the masses and relative abundances of all the element's naturally occurring isotopes. The atomic mass unit (amu) or unified atomic mass unit (u) is the standard unit for expressing atomic masses.
To calculate the atomic mass, you multiply the mass of each isotope by its fractional abundance and then sum these products. For instance, if an element has two isotopes with masses of 10 u and 11 u existing in equal proportions (50%), the atomic mass would be (0.50×10) + (0.50×11) = 10.5 u.
In practice, this calculated atomic mass is what is displayed under the element's symbol on the periodic table, providing a convenient reference for scientists and students. The listed atomic mass on the periodic table allows chemists to predict the behavior of the element in various reactions and determine the element's molar mass for quantitative analysis in chemistry.