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scan0008 - 310 Chapter8 Bonding Basics to our health It is...

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Unformatted text preview: 310 Chapter8 Bonding Basics to our health. It is just not the best thing that could happen to our house— hold pipes. If the buildup is bad enough, the pipes can become clogged, much as heart arteries become clogged with fatty plaques, reducing blood flow in a human. Many homeowners and some cities “soften” water by passing it through a bed of zeolites, which exchange the calcium ions for sodium ions that (remember our solubility rules) do not form insoluble salts. How do these ion—exchanging zeolites work? Zeolites like that shown in Figure 8.6 are composed of aluminum and silicon oxide subunits containing Group IA and IIA cations. The resulting honeycomb arrangement of subunits results in a structure full of atom— sized holes. Ions and molecules small enough to fit through these holes can enter the zeolite, and if they are just about the same size as the holes in the "Hard" water contains relatively high concentra- zeolite, they get stuck inside. Interactions of the ions or molecules with the “0“5 0f calcrum, typically along W'th magnesium zeolite help to hold them inside. Substances that are too small easily flow in and iron. The rock-like deposits of calcium car- bonate that form on the inside of hot water pipes give hard water its name. Application CHEMICAL . ENCOUNTERS: E Focus on Zeolites Visualization: Ionic Radii FIGURE 8.6 Ions can enter, and they can leave: The structure of natrolite and sodalite. These zeolites have pores that ions of the right size can enter. and out of the zeolite, whereas ions and molecules that are too big can’t enter the zeolite in the first place. Consequently, a zeolite retains only spe~ cific sizes of ions and molecules. In exchange for the trapped ions, the zeo- lite releases ions of the same total charge. For example, when a calcium ion is taken up by the zeolite, it typically releases two sodium ions. By carefully constructing the zeolite, researchers have been able to develop an “ionic sponge” that grabs only the ions of interest to them. This is vital, in the chemical industry, to the formation of better reaction catalysts (compounds that significantly increase the rate of a chemical reaction without being consumed) the filtration of polluted air, and the cleanup of hazardous wastes, among other applications. Experiments with the zeolite known as clinoptilolite, with a pore size of 0.4 nm, indicated that it was capable of removing radioactive cesium (134Cs and 137Cs) from cows affected by the 1986 Chernobyl (Ukraine) nuclear accident. By far the most common use of zeolites is as an ingredient called a “builder” in laundry detergents for the removal of calcium ions from hard water. Size is a critical factor in the behavior of ionic compounds. Not only does size suggest what type of zeolite can trap a particular ion, it also plays a major role in deter- mining the structure of the ionic crystal and the strength of the ionic bond. What contributes to the size of an ion? We can examine the electrons in an atom more closely to determine the answer. In our previous discussion of the shape of the orbitals (Chapter 6), we learned that the electrons penetrate deep into the atom. Each electron helps to balance the charge of the protons in the nu— cleus and shields the other electrons from the nuclear charge. When an electron Natrolite Sodalite ...
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