What is the average atomic mass of this element

Question

Problems SetB » SummerB_08
A newly discovered element is found to have four isotopes. The first isotope has a mass of 628.7 amu and a percent abundance of 24.21 %. The second isotope has a mass of 629.7 amu and a percent abundance of 28.75 %. The third isotope has a mass of 631.7 amu and a percent abundance of 16.65 %. The fourth isotope has a mass of 634.7 amu. What is the average atomic mass of this element?

Answer 1

m₁ = 628.7

m₂ = 629.7 

m₃ = 631.7

m₄ = 634.7

 

A₁ = 24.21

A₂ = 28.75

A₃ = 16.65

A₄ =  100 - (24.21 + 28.75 + 16.65)

 

The average atomic mass is

 

<m> = (m₁A₁ + ... + m₄A₄)/(A₁ + ... + A₄)

 

Now just plug in the numbers and finish from here.