To determine the relative atomic mass of an ion, we need to consider the isotopic composition of the element from which the ion is derived. The iodine ion with a single negative charge, I^-, is an anion derived from the element iodine (I).
Iodine has several isotopes, including iodine-127 (^127I) and iodine-129 (^129I), with natural abundances of approximately 100% and 0.01%, respectively.
To calculate the relative atomic mass of the I^- ion, we consider the weighted average of the isotopic masses based on their abundances.
Relative atomic mass (I^-) = (Relative atomic mass of ^127I * Abundance of ^127I) + (Relative atomic mass of ^129I * Abundance of ^129I)
Plugging in the values:
Relative atomic mass (I^-) = (127 * 1.00) + (129 * 0.01) = 127.01
Therefore, the relative atomic mass of the I^- ion is approximately 127.01 atomic mass units (amu).