Question 2.5: Chlorine has two naturally occurring isotopes: 17^35Cl with ......

STRATEGY

The atomic mass of an element is the weighted average of the isotope masses, which equals the sum of the masses of each isotope times the natural abundance of that isotope:

Atomic mass = (\text{mass of}  ^{35}_{17}Cl) (\text{Abundance of}  ^{35}_{17} Cl)  + (\text{mass of}  ^{37}_{17}Cl) (\text{Abundance of}  ^{37}_{17} Cl)

Atomic mass = (34.969  amu) (0.7577)  +  (36.966  amu) (0.2423) = 35.45  amu