Stability of Nucleus
The nucleus is not involved in normal chemical reactions. In radioactivity, it is the nucleus that is undergoes the changes. Nuclear forces are extremely strong forces that hold the nuclear particles together. These forces make the nucleus very stable. Remember that the protons are positively charged and can exert repulsive forces among themselves. It has been found out that there are certain predictable behavioral patterns in elements as the atomic number increases. As the atomic number increases, the neutron-to-proton ratio increases and as more and more protons are present in the nucleus, the stabilizing forces are not sufficient to keep the nucleus stable. Thus the stability of the nucleus decreases as the neutron-to-proton ratio increases.