Oxygen ionic compound with calcium

As our final illustration of ionic bonding, consider the reaction of calcium (Group DA) with oxygen (Group VIA). This reaction forms calcium oxide, a white solid ionic compound with a very high melting point, 2580°C. 

For complete neutralization to take place, the proper amounts of acid and base must be present. The salt formed in the above reaction is NaCl. If the water were evaporated after completing the reaction, we would be left with common table salt. Sodium chloride is just one of hundreds of salts that form during neutralization reactions. While we commonly think of salt, NaCl, as a seasoning for food, in chemistry a salt is any ionic compound containing a metal cation and a nonmetal anion (excluding hydroxide and oxygen). Some examples of salts that result from neutralization reactions include potassium chloride (KCl), calcium fluoride (CaF ), ammonium nitrate (NH NOj), and sodium acetate (NaC2H302). 

Alkali-earth metals (calcium, barium, and magnesium) complex with polysaccharides extensively (Reisenhofer et al., 1984). Calcium has a smaller atomic and ionic radius than does sodium and, because it has two valence electrons, it is endowed with greater polarizing and bonding ability than Na+. Ca and Ca2+ easily form insoluble complexes with oxygenated compounds. Polysaccharide salts of alkali-earth metals are generally insoluble. 

This tells us that 2 molecules of hydrogen chloride (in hydrochloric acid) will react with 1 formula unit of calcium carbonate (as it contains a metal it must be an ionic compound), but it does not tell us how much hydrogen chloride in grammes we must add to the calcium carbonate to ensure that all the calcium carbonate is used up. But if we use moles all is much clearer. The relative formula mass of calcium carbonate is 40 (from calcium) -1-12 (from carbon) -I- (3 X 16) (from oxygen) = 100. So 1 mole of calcium carbonate has a mass of 100 g. Then for every 100 g of calcium carbonate we are reacting we will need to use 2 x 36.5g(=73g) of hydrogen chloride. 

First, let us imagine the particles making up the Ca(N03)2 solution. Remember that when ionic compounds dissolve, the ions separate and become surrounded by water molecules. When Ca(N03)2 dissolves in water (Figure 4.7), the Ca ions separate from the NO3 ions, with the oxygen ends of water molecules surrounding the calcium ions, and the hydrogen ends of water molecules surrounding the nitrate ions. 

To show how to predict which ions form when a metal reacts with a non-metal, we will consider the formation of an ionic compound from calcium and oxygen. We can predict the compound that will form by considering the valence electron configurations of the two atoms. 

The term oxidation is used because the first reactions of this sort to be studied thoroughly were reactions with oxygen. Many metals react directly wifli O2 in air to form metal oxides. In these reactions the metal loses electrons to oxygen, forming an ionic compound of the metal ion and oxide ion. For example, when calcium metal is exposed to air, the bright metallic surface of the metal tarnishes as CaO forms ... 

To best illustrate all of the information contained in a chemical formula, consider the moderately complicated example of calcium phosphate, Ca3(P04)2. This compound is composed of Ca + ions, each of which has a +2 charge, and phosphate ions, P04 , each with a -3 charge. The 4 oxygen atoms and the phosphorus atom in the phosphate ion are held together with covalent bonds. The calcium and phosphate ions are bonded together ionically in a lattice composed of these two kinds of ions. Therefore, both ionic and covalent bonds are involved in calcium phosphate. Figure 4.16 summarizes the information contained in the calcium phosphate formula. 

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