Giant ionic compounds

The attractions between positive ions (cations) and negative ions (anions) are strong, and ionic compounds have a giant lattice stmcture. 

The elements sodium and chlorine react together to form the compound sodium chloride, which has a giant ionic lattice structure. 

There are three types of giant structure - ionic, metallic and macromolecular. a Sodium nitride is an ionic compound. Draw a diagram that shows the formula of the compound, the charges on the ions and the arrangement of the valency electrons around the negative ion. 

The hundreds of ions holding each other together make ionic compounds giant structures, but the ratio of the positive to negative ions is always the same, e.g. one Na+ to every one Cl (Figure 7.3). 

Since ionic compounds exist as giant ionic structures (Chapter 4) the concept of a molecule cannot be applied. The formula of an ionic compound is therefore an empirical formula, representing the ions present in their simplest ratio. 

Ionic lattices have a three-dimensional arrangement of alternating positive and negative ions. Compounds with ionic lattices are sometimes called giant ionic structures. 

Ionic compounds such as sodium chloride and magnesium oxide form a giant three-dimensional lattice structure containing ions in a regularly repeating pattern. 

In contrast to the ion exchange theory, much evidence indicates that cells have an active ion pump that removes Na+ from cells and introduces K+. For example, the cytoplasm of the giant axons of nerves of squid can be squeezed out and replaced by ionic solutions. Erythrocyte ghosts can be allowed to reseal with various materials inside. Ion transport into or out of cells has been demonstrated with such preparations and also with intact cells of many types. Such transport is blocked by such inhibitors as cyanide ion, which prevents nearly all oxidative metabolism. However, the cyanide block can be relieved by introduction into the cells of ATP and other phosphate compounds of high group-transfer potential. 

Radioactive 109Cd has been used in a study of the unicellular giant alga Acetabularia acetabulum (Karez et al., 1991). After incubation with 109Cd, extracts were eluted from a Sephacryl S-200 column. After short incubations of 1 - 2 h ionic and low molecular weight compounds were eluted, thus little or no cadmium was immobilised, but for incubation times of one week or more cadmium was associated with fractions with molecular weights of more than 25000 D and between 70000 and 20000 D. 

Other inorganic compounds have a variety of crystal shapes, in all of which the ions, atoms or molecules are arranged in a definite pattern, held together by ionic or covalent bonds, or by intermolecular attractions, which arise from the polarity (or electrical asymmetry) of the molecules. In diamond, for example, each carbon atom is covalently bonded to four neighbours (Fig. 9) so that the crystal is one giant molecule . This in part accounts for its great strength and hardness. 

Detailed discussions on supramolecular structures of giant polyoxometalate clusters have been reported by Muller and co-workers." " The number of ionic lattices formed from anionic POM clusters and organic cations-coordination complex cations resulting in supramolecular structures is substantial and literally more than hundreds of new compounds in this class appear annuallyIn this overview, the supramolecular features of POM-based systems will be discussed mainly under three headings (a) supramolecular features of polyoxometalate supported transition metal complexes, (b) polyoxometalate-crown ether complexes with supramolecular cations, and (c) supramolecular water clusters associated with polyoxometalates. 

---