To find the mass of an isotope, you need to know the atomic mass of the element and the abundance of the specific isotope. Here's how you can calculate the mass of an isotope:
Determine the atomic mass of the element: The atomic mass of an element is usually provided on the periodic table. It represents the weighted average of the masses of all the naturally occurring isotopes of that element. The atomic mass is given in atomic mass units (amu) or grams per mole (g/mol).
Identify the abundance of the isotope: Isotopes of an element have different numbers of neutrons, but the same number of protons. Each isotope has a specific abundance, which represents the percentage of that isotope present in nature. The abundance can also be given as a decimal or fraction.
Calculate the mass of the isotope: To find the mass of the isotope, multiply the atomic mass of the element by the abundance of the isotope. This accounts for the contribution of that isotope to the overall atomic mass of the element.
Mass of isotope = Atomic mass of the element × Abundance of the isotope
For example, let's say you want to find the mass of the carbon-12 isotope (C-12). Carbon has an atomic mass of approximately 12.01 amu, and the abundance of carbon-12 is 98.93%.
Mass of C-12 = 12.01 amu × 0.9893 Mass of C-12 ≈ 11.87 amu
Therefore, the mass of the carbon-12 isotope is approximately 11.87 atomic mass units (amu).