Problem: The element lead (Pb) consists of four naturally occurring isotopes with atomic masses 203.97302, 205.97444, 206.97587, and 207.97663 amu. The relative abundances of these four isotopes are 1.4, 24.1, 22.1, and 52.4%, respectively.From these data, calculate the atomic weight of lead.

$\boxed{\mathbf{atomic}\mathbf{ }\mathbf{weight}\mathbf{ }\mathbf{=}\mathbf{ }{[\mathrm{mass}\times f.a.]}_{\mathbf{isotope}\mathbf{ }\mathbf{1}}\mathbf{ }\mathbf{+}\mathbf{ }\mathbf{ }{[\mathrm{mass}\times f.a.]}_{\mathbf{isotope}\mathbf{ }\mathbf{2}}\mathbf{ }\mathbf{+}\mathbf{ }\mathbf{ }{[\mathrm{mass}\times f.a.]}_{\mathbf{isotope}\mathbf{ }\mathbf{3}}\mathbf{ }\mathbf{+}\mathbf{ }{[\mathrm{mass}\times f.a.]}_{\mathbf{isotope}\mathbf{ }\mathbf{4}}}$

isotope 1: mass = 203.97302 amu              f.a. = 1.4% ÷ 100 = 0.014

isotope 2: mass = 205.97444 amu              f.a. = 24.1% ÷ 100 = 0.241

isotope 3: mass = 206.97587 amu              f.a. = 22.1% ÷ 100 = 0.221

isotope 4: mass = 207.97663 amu              f.a. = 52.4% ÷ 100 = 0.524