1. Average Atomic Mass

2. Average atomic mass
On the periodic table, the mass number is not shown, instead the average atomic mass
Average atomic mass is the average mass of all the element’s naturally occurring isotopes, taking into account the proportions of those isotopes on Earth

3. Example 1
Carbon has two naturally occurring isotopes C-12 and C-14 and an average atomic mass is Which isotope is more common on Earth?
Carbon 12

4. Calculating Average Atomic Mass
(R.A. of Iso. 1) x (Mass Iso 1) + (R.A. Iso 2) x (Mass Iso 2)

5. Example 2
Copper has two naturally occurring isotopes % Copper-63 and 30.83% Copper-65. Find the average atomic mass of copper.

6. Example 3
Magnesium has 3 naturally occurring isotopes Mg %, Mg %, and Mg %. What is the average atomic mass of the element?