The primary chemical composition of kidney stones commonly includes Ca₃(PO₄)₂ (calcium phosphate), CaC₂O₄ (calcium oxalate), and MgNH₄PO₄ (magnesium ammonium phosphate). The metal ions in these compounds are:

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11ecba2d_11f8_69c4_a3bf_f72414ca96cf_MD0008_00 Ionic compounds contain one or more ionic bonds, which result from electrostatic attractions between ions with opposite charges. The charges may be from individual ionized atoms or from polyatomic ions. An ionic bond between two atoms often involves the transfer of valence electrons from one atom (typically a metal) to another (typically a nonmetal) to create a cation and an anion. Because of their relatively low electronegativity and ionization energy, metals tend to lose electrons to form cations whereas nonmetals tend to gain electrons to form anions. The charge of an atomic ion relates directly to the number of electrons gained or lost. For each electron lost, the charge increases by one unit, but for each electron gained, the charge decreases by one unit. The electron-deficient character of metal cations causes them to be attracted to electron-rich ions or molecules and act as Lewis acids. The strength of the attraction increases as the ionic charge increases or as the ionic radius decreases. As a result, metal cations with a smaller ionic radius and a higher positive charge such as Al³⁺ and Ti⁴⁺ are stronger Lewis acids than metal cations with a larger ionic radius and lower charge such as Ca²⁺ and Mg²⁺. The alkaline-earth metals Ca and Mg each have two valence electrons, which are easily lost during oxidation in natural systems to form cations with a +2 charge. (Choice A) Calcium and magnesium are alkaline-earth metals (Group 2), not alkali metals (Group 1). (Choice B) The relatively large cationic radii and low charge of Ca²⁺ and Mg²⁺ make these ions weak Lewis acids. (Choice C) Ca²⁺ and Mg²⁺ cations are produced by the oxidation of elemental Mg and Ca metals, not by reduction. Educational objective: Metals tend to lose electrons to form cations whereas nonmetals tend to gain electrons to form anions. The charge of an atom increases by one unit for each electron lost but decreases by one unit for each electron gained. Metal cations with a smaller ionic radius and a higher positive charge are stronger Lewis acids than those with a larger ionic radius and lower charge.

The Primary Chemical Composition of Kidney Stones Commonly Includes Ca3(PO4)2

The Primary Chemical Composition of Kidney Stones Commonly Includes Ca₃(PO₄)₂