Average Atomic Mass
How can you find the average atomic mass of an element, if you're given the isotopic abundances and the mass of each isotope?
In nature, there are three types of magnesium:
Mg-24 has a mass of 23.985 amu and accounts for 78.70% of all magnesium
Mg-25 has a mass of 24.985 amu and accounts for 10.13% of all magnesium
Mg-26 has a mass of 25.983 amu and accounts for 11.17% of all magnesium
What is magnesium's average atomic mass?
In nature, there are three types of magnesium:
Mg-24 has a mass of 23.985 amu and accounts for 78.70% of all magnesium
Mg-25 has a mass of 24.985 amu and accounts for 10.13% of all magnesium
Mg-26 has a mass of 25.983 amu and accounts for 11.17% of all magnesium
What is magnesium's average atomic mass?
Answer:
Each percentage here is called the isotopic abundance of that particular isotope.
The average atomic mass (mass on the periodic table) is a weighted average of all isotopes.
Average Atomic Mass = (% of isotope 1)(mass of isotope 1)
+ (% of isotope 2)(mass of isotope 2) + ...
In this case, the average atomic mass of magnesium is
(0.7870)(23.985 amu) + (0.1013)(24.985 amu) + (0.1117)(25.983 amu)
= 24.309 amu
Each percentage here is called the isotopic abundance of that particular isotope.
The average atomic mass (mass on the periodic table) is a weighted average of all isotopes.
Average Atomic Mass = (% of isotope 1)(mass of isotope 1)
+ (% of isotope 2)(mass of isotope 2) + ...
In this case, the average atomic mass of magnesium is
(0.7870)(23.985 amu) + (0.1013)(24.985 amu) + (0.1117)(25.983 amu)
= 24.309 amu
