Question

Three isotopes of silicon have mass numbers of 28,29, and 30 with an average atomic mass of 28.086 what does this say about the relative abundances of the isotopes

Answer 1

Answer is: silicon isotope with mass number 28 has highest relative abundance, this isotope is the most common of these three isotopes.

Ar₁(Si) = 28; the average atomic mass of isotope ²⁸Si.  

Ar₂(Si) =29; the average atomic mass of isotope ²⁹Si.  

Ar₃(Si) =30; the average atomic mass of isotope ³⁰Si.  

Silicon (Si) is composed of three stable isotopes, ₂₈Si (92.23%), ₂₉Si (4.67%) and ₃₀Si (3.10%).

ω₁(Si) = 92.23%; mass percentage of isotope ²⁸Si.  

ω₂(Si) = 4.67%; mass percentage of isotope ²⁹Si.

ω₃(Si) = 3.10%; mass percentage of isotope ³⁰Si.

Ar(Si) = 28.086 amu; average atomic mass of silicon.  

Ar(Si) = Ar₁(Si) · ω₁(B) + Ar₂(Si) · ω₂(Si)  + Ar₃(Si) · ω₃(Si).  

28,086 = 28 · 0.9223 + 29 · 0.0467 + 30 · 0.031.