Final answer:
The isotopic abundance of an element is determined using a mass spectrometer that measures the deflection of ions to display peaks on a mass spectrum. The height of each peak is proportional to the isotop’s abundance, which can then be used to calculate the element's atomic mass.
Step-by-step explanation:
The isotopic abundance of an element can be accurately determined using a mass spectrometer. In this process, first, a sample is vaporized and exposed to a high-energy electron beam which ionizes the sample's atoms. These ions are then deflected by a magnetic field in the mass spectrometer, with the path's deflection depending on their mass-to-charge ratio.
These deflections are depicted as peaks on a mass spectrum, where the height of each peak corresponds to the relative abundance of each ion. By comparing the peak heights (which reflect abundance) with known mass-to-charge ratios of the isotopes, chemists can calculate the fractional abundances of isotopes. Using the known masses of these isotopes, along with their calculated fractional abundances, one can then compute the average atomic mass of the element.
An important point to note is that natural abundance may vary slightly depending on the source of the element, according to the IUPAC/CIAAW. However, the atomic mass listed in the periodic table is a weighted average taking into account the abundances of the isotopes and allowing us to calculate the atomic mass of elements in naturally occurring samples with precision.