**Practice Problem 5**

Calculate the binding energy of ^{235}U if the mass of this nuclide is
235.0349 amu.

**Solution**

A neutral ^{235}U atom contains 92 protons, 92 electrons, and
143 neutrons. The predicted mass of a ^{235}U atom is
therefore 236.9601 amu, to four significant figures:

[92(1.00728) amu] + [92(0.0005486) amu] + [143(1.00867) amu] = 236.9601 amu

total mass = 236.9601 amu

To calculate the mass defect for this nuclide, we subtract the observed mass from the predicted mass:

236.9601 amu - 235.0349 amu = 1.9252 amu

mass defect = 1.9252 amu

Using the conversion factor that relates the binding energy to the mass
defect, we obtain a binding energy for ^{235}U of 1793.3 MeV per atom: