Question

Question #c7df4

Answer 1

Average atomic weights (as given by The Periodic Table of the Elements) for elements are the weighted averages of the atomic weights of the individual isotopes for those elements.

Explanation:

For example, take the element Hydrogen, with the atomic symbol `"H"`.

Hydrogen, as shown in the diagram above, has three isotopic forms: Protium, Deuterium, and Tritium. These isotopes have relative abundances of:

Protium: `99.98%`, Atomic weight: `1.0078`
Deuterium: `0.015%`, Atomic weight: `2.014`
Tritium: `0.005%`, Atomic weight: `3.016`

You may have slightly different values depending on your teacher or textbook, but that's besides the point.

Anyway, if we were to take the weighted average of the atomic weights of the three isotopes of Hydrogen to get the weighted average atomic weight (as listed on your Periodic Table), we would get this:

`("Relative abundance of Protium")*("Atomic weight of Protium") + ("Relative abundance of Deuterium")*("Atomic weight of Deuterium") + ("Relative abundance of Tritium")*("Atomic weight of Tritium") = "Weighted Average Atomic Mass of Hydrogen"`

`0.9998(1.0078) + 0.015(2.014) + 0.005(3.016)= 1.008`

Therefore, the weighted average atomic weight of Hydrogen would be `1.008` for this example.

I hope that helps!