Why is atomic mass an average?

Answer 1

In short:
Average atomic mass = (% as dec.)(mass of isotope 1) + (% as dec.)(mass of isotope 2) + ....

As shown above, the atomic mass of an element is the average of the isotopes of that element.

For example, the average atomic mass of lithium will be calculated by using lithium's two isotopes, Li-6 and Li-7: Average atomic mass = (0.9258)(7.015) + (0.0742)(6.015) = 6.940 u

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Answer 2

Kai Bowman

Atomic mass is an average because it accounts for the isotopes of an element, which have different masses due to variations in the number of neutrons. The atomic mass listed on the periodic table is a weighted average of the masses of all naturally occurring isotopes of that element, taking into account their relative abundances.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.