Atomic and Nuclear Physics
MASS DEFECT AND BINDING ENERGY
Since 1 amu is equivalent to 931.5 MeV of energy, the binding energy can be calculated using
B.E. D m
Calculate the mass defect and binding energy for uranium-235. One uranium-235 atom
has a mass of 235.043924 amu.
Step 1: Calculate the mass defect using Equation (1-1).
A Z mn
235 92 1.008665 amu 235.043924 amu
D m 1.91517 amu
Step 2: Use the mass defect and Equation (1-2) to calculate the binding energy.
B.E. D m
Energy Levels of Atoms
The electrons that circle the nucleus move in fairly well-defined orbits. Some of these electrons
are more tightly bound in the atom than others.
For example, only 7.38 eV is required to
remove the outermost electron from a lead atom, while 88,000 eV is required to remove the
innermost electron. The process of removing an electron from an atom is called ionization, and
the energy required to remove the electron is called the ionization energy.
In a neutral atom (number of electrons = Z) it is possible for the electrons to be in a variety of
different orbits, each with a different energy level. The state of lowest energy is the one in which
the atom is normally found and is called the ground state. When the atom possesses more energy
than its ground state energy, it is said to be in an excited state.