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

Mar 7, 2017

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:

$\left(0.7553 \times 35 + 0.2447 \times 37\right) \cdot \text{amu}$

$=$ $35.46 \cdot \text{amu}$, which is very near the atomic mass quoted on the Periodic Table (they are slightly different because the Table considers minor isotopes).