# How can an average atomic mass be calculated?

May 25, 2018

The average atomic mass, the mass quoted on the Periodic Table, is the WEIGHTED average of the individual isotopes...

#### Explanation:

Let's take a pertinent example... All chlorine in the universe so far as we know, is 75.8% ""^35Cl and 24.2% ""^37Cl...and to get the average atomic mass, we sum appropriately...

{75.8%xx35+24.2%xx37}*"amu"

$= 35.5 \cdot \text{amu}$

And if you look at the Periodic Table beside you now, you find that it lists the atomic mass of chlorine as $35.5 \cdot g \cdot m o {l}^{-} 1$. Capisce?