Naturally occurring lead exists as four stable isotopes:^204 Pb with a mass of 2

Question

Naturally occurring lead exists as four stable isotopes:^204 Pb with a mass of 203.973 amu (1.480%);^206 Pb, 205.974 amu (23.60%);^207 Pb, 206.9759 amu (22.60%; and^208 Pb, 207.9766 amu (52.30%). Calculate the average atomic mass of lead. An aluminum atom has an average diameter of about 3.0 times 10^-8 cm. The nucleus has a diameter of about 2.0 times 10^-13 cm. Calculate the ratio of the atomic volume to nuclear volume for an atom of aluminum. Assume that an atom is spherical (V = (4/3) pi r^3)

Explanation / Answer

Ans 3. Average atomic mass can be calculated by summing the masses of individual isotopes of lead, each multiplied by its natural abundance.

So M = [ (1.480 × 203.973) + ( 23.60 × 205.974) + ( 22.60 + 206.9759 ) + ( 52.30 × 207.9766) ] / 100

M = 207.1769 amu

So the average atomic mass of lead is 207.1769 amu

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