In ionic bonding, electrons are completely transferred from one atom to another. In the process of either losing or gaining negatively charged electrons, the reacting atoms form ions. The oppositely charged ions are attracted to each other by electrostatic forces, which are the basis of the ionic bond.
Entropy is a measure of the degree of the spreading and sharing of thermal energy within a system. The entropy of a substance increases with its molecular weight and complexity and with temperature. The entropy also increases as the pressure or concentration becomes smaller.
Thus the entropy change of the universe during reversible processes is zero. During an adiabatic process no heat flows. Thus from we see that the entropy change of a system during for a reversible, adiabatic process is zero.