scan0014 - 316 ChapterS Bonding Basics F,GUR,E,:9 Common...

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Unformatted text preview: % 316 ChapterS Bonding Basics F',GUR,E..,§:9 Common table sugar. Sugar can be crystallized in large chunks that look much like the crystals of table salt. Cough syrups often contain ethanol (listed on the ingredient label as alcohol) to increase the solubility of the active compounds in the medicine that would otherwise not be sufficiently soluble in water. has a larger, more positive lattice enthalpy. And indeed it does (2609 kI/mol versus 2223 kI/mol). Aluminum chloride (AlCl3) and sodium chloride (NaCl) differ in the charge of the cation. The larger charge on the aluminum cation (+3) indicates that alu— minum chloride should have the larger lattice enthalpy. It does (5376 kI/mol versus 787 kl/mol). Further Insights Which has a greater influence on the lattice enthalpy, ionic radius or ionic charge? The examples we’ve examined suggest that the ionic charge has a much greater effect. We can reason, and rightly so, that the electrostatic force of attraction be— tween a cation and an anion is a very powerful force. This powerful force assists some proteins as they fold into a biologically active molecule. PRACTICE 8.4 Which has the greater lattice enthalpy, FeC13 or FeClz? See Problems 25, 26, 33, 34, 100, 101, and 103. eag8;3g Covalent Bonding In addition to NaCl (table salt), sucrose (C12H22011, common sugar) is another compound we see at the dinner table (Figure 8.9). What is the difference between table salt and sugar? Placed side by side, they appear relatively similar to the naked eye. Both are colorless crystalline compounds. When added to water, they both dissolve. However, as we saw in Chapter 4, solutions of these two com— pounds act differently. Table salt, a strong electrolyte, dissociates into sodium cations and chloride anions when dissolved in water. Sucrose, a nonelectrolyte, doesn’t dissociate when it dissolves. This is why electric current passed through the salt solution and lit the bulb, while the bulb over the sugar solution remained unlit. Sucrose is an example of a compound containing only covalent bonds. The atoms that make up sugar are firmly held together; bonds between these atoms don’t dissociate upon addition to water. Because of this, an aqueous solution of sucrose doesn’t conduct electricity. These bonds differ from the bonds in sodium chloride, an ionic compound that dissociates in water, because the electrons in sucrose are shared. ' Knowing the type of the bonds that make up a molecule is fundamental to those who do chemistry for a living. For example, pharmacognocists understand that whereas many ionic compounds are readily soluble in water and can be u u ( Directions - use dose cup, teaspoon 3. or flotsam - do not exceed 4 doses {$34 More adults and children 12 years and over children 6 to under 12 years every 6 —» children under 6 years Other information ~ each tablespoon contains sodium 31 - store at room temperature rn :paflive ingredients co 0 , carboxymethylcelluiose sodium cit ‘ blue no. 1, map red no. 40, flavor, high in polyethylene oxrde, polyoxyl 4O stearate. or purified water, sacs ' - citrate harm sodium, sodium b ...
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