Answer
a) $24.30\text{ amu}$
b) $50.94\text{ amu}$
Work Step by Step
To calculate the atomic weight of an element, we use the weighted average of its isotopes:
Atomic Weight
=∑(Isotopic Mass × Fractional Abundance)
a) Magnesium
Atomic Weight
$=(23.99\times0.7899)+(24.99\times0.1000)+(25.98\times0.1101)$
$=18.94+2.50+2.86$
$=24.30\text{ amu}$
b) Vanadium
Atomic Weight
=
$(49.95\times 0.00250)+(50.94\times 0.99750)$
$=0.125+50.81$
$=50.94\text{ amu}$
