Chapter 7, Problem 133AP

Both ${\text{Mg}}^{\text{2+}}{\text{and Ca}}^{\text{2+}}$ are important biological ions. One of their functions is to bind to the phosphate group of ATP molecules or amino acids of proteins. For Group 2A metals in general, the tendency for binding to the anions increases in the order ${\text{Ba}}^{\text{2+}}{\text{< Sr}}^{\text{2+}}{\text{< Ca}}^{\text{2+}}{\text{< Mg}}^{\text{2+}}$. Explain this trend.