Review the loss of energy and mass between the assembled nucleus and the nucleons. Relate the difference as mass deficit and binding energy determined by Einstein's formula. Discuss that nuclei are more stable as the atomic mass approaches 56 (iron) and that atoms below mass of 56 will naturally gain mass to approach 56. Atoms above 56 will naturally lose mass to approach 56. Examples of hydrogen to helium and uranium to thorium were used. The need for neutrons in a heavy nucleus to increase the strong force was discussed and keep the nucleus together.