Question

Why are the atomic masses of elements usually decimal numbers?

Answer 1

Atomic masses are average masses of the different isotopes of that element that occur naturally. For example, the mass of Cl-35 and the mass of Cl-37 are averaged (about 76% for 35 and 24% for 37) and the weighted average is about 35.5 for naturally occurring Cl2.

Answer 2

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