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The isotopic mass is one of the fundamental concepts in understanding how to calculate the average atomic mass of an element. Every element has isotopes, which are atoms with the same number of protons but different numbers of neutrons. This variation in neutron number results in a slight difference in mass amongst isotopes of the same element. The isotopic mass is measured in atomic mass units (amu), with each unit roughly equivalent to the mass of a single proton or neutron.

When you encounter the isotopic mass in a problem, it refers to the mass of a particular isotope as compared to the mass of a carbon-12 atom, which is defined as exactly 12 amu. It's essential to remember that isotopic masses can be looked up on the periodic table or given scientific resources, as they are constant for each isotope of every element.

To comprehend the concept of isotope abundance, think about it as the percentage of an isotope present in a naturally occurring sample of an element. Since elements consist of mixtures of isotopes, the abundance can greatly influence the overall average atomic mass of an element. The isotope abundance is usually expressed as a percentage but must be converted into a decimal form to be used in calculations.

For instance, if isotope X has an abundance of 50%, its decimal form would be 0.50 in calculations. The higher the abundance of a particular isotope, the more it will contribute to the average atomic mass of that element. Accurately determining the abundance of each isotope is crucial since this data affects the outcome of your average atomic mass calculation significantly.

Atomic mass units (amu) serve as the standard unit for expressing atomic and molecular masses. It's a very tiny unit of mass, tailored for use in the atomic scale, where traditional units like grams or kilograms are impractical due to their largeness. One atomic mass unit is defined as one-twelfth the mass of a carbon-12 atom, which equates to about 1.66053906660(50)x10^-27 kilograms, providing a baseline to measure all other atomic masses.

The use of amu allows scientists and students to talk about atomic masses in a comprehensible way, without resorting to incredibly small numbers denoted by the kilogram system. When calculating average atomic mass, expressing the final result in amu is not just a convention but a necessity for clarity and consistency, especially in scientific discussions and literature.