# Why is the atomic mass of chlorine quoted on the Periodic Table NON-INTEGRAL?

All chlorine nuclei have 17 protons in their nucleus. Chlorine nuclei contain differing numbers of neutrons. The weighted average of the nuclei sum to $35.45$ amu.
Isotopic breakdown of chlorine: ""^35Cl, 75.77%; ""^37Cl, 24.27%. These are the major isotopes and their weighted average is the quoted atomic mass.