Question

How can chlorine have an atomic mass of `35.45*"amu"`?

Answer 1

The atomic mass quoted on the Periodic Table is simply the WEIGHTED average of the individual isotopic masses of an element.

Explanation:

We can calculate the average atomic mass of the element chlorine, given that its isotopic distribution is: `""^35Cl, 75.53%; ""^37Cl, 24.47%`.

And the weighted average of the masses is:

`(0.7553xx35+0.2447xx37)*"amu"`

`=` `35.46*"amu"`, which is very near the atomic mass quoted on the Periodic Table (they are slightly different because the Table considers minor isotopes).