O bjective 31 o bjective 31 e xample 36 n aming m

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O BJECTIVE 31 O BJECTIVE 31 E XAMPLE 3.6 - N AMING M ONATOMIC I ONS Write names that correspond to the following formulas for monatomic ions: (a) Ba 2 + , (b) S 2 , and (c) Cr 3 + . Solution a. Because barium is in group 2, the only possible charge is + 2. When there is only one possible charge, metallic ions are named with the name of the metal. Therefore, Ba 2 + is barium ion . b. Monatomic anions are named with the root of the nonmetal and ‑ide, so S 2 is sulfide ion . c. Because chromium is not on our list of metals with only one possible charge, we need to indicate the charge with a Roman numeral. Therefore, Cr 3 + is chromium(III) ion . O BJECTIVE 31 E XERCISE 3.6 - N AMING M ONATOMIC I ONS Write names that correspond to the following formulas for monatomic ions: (a) Mg 2 + , (b) F , and (c) Sn 2 + .
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E XAMPLE 3.7 - F ORMULAS FOR M ONATOMIC I ONS Write formulas that correspond to the following names for monatomic ions: (a) phosphide ion, (b) lithium ion, and (c) cobalt(II) ion. Solution a. We know this is a monatomic anion because it has the form, (nonmetal root) ide . Phosphorus atoms gain three electrons to get 18 electrons like the noble gas argon, Ar. Phosphide ion is P 3 . b. Lithium atoms lose one electron to get two electrons, like the noble gas helium. Lithium ion is Li + . c. The Roman numeral indicates that the cobalt ion has a + 2 charge. Note that we would not have been able to determine this from cobalt’s position on the periodic table. Cobalt(II) is Co 2 + . O BJECTIVE 31 E XERCISE 3.7 - F ORMULAS FOR M ONATOMIC I ONS Write formulas that correspond to the following names for monatomic ions: (a) bromide ion, (b) aluminum ion, and (c) gold(I) ion. O BJECTIVE 31 Several of the monatomic cations play important roles in our bodies. For example, we need calcium ions in our diet for making bones and teeth. Iron(II) ions are found in hemoglobin molecules in red blood cells that carry oxygen from our lungs to the tissues of our bodies. Potassium, sodium, and chloride ions play a crucial role in the transfer of information between nerve cells. Enzymes (chemicals in the body that increase the speed of chemical reactions) often contain metallic cations, such as manganese(II) ions, iron(III) ions, copper(II) ions, and zinc ions. For example, Zn 2 + ions are in the center of the enzyme alcohol dehydrogenase, which is the enzyme in our livers that accelerates the breakdown of the ethanol consumed in alcoholic beverages. Structure of Ionic Compounds Figure 3.18 shows the solid structure of the ionic compound sodium chloride, NaCl. We have already seen that the particles that form the structure of ionic compounds are cations and anions, and the attractions that hold them together are ionic bonds. When atoms gain electrons and form anions, they get larger. When atoms lose electrons and form cations, they get significantly smaller. Thus the chloride ions are larger than the sodium ions. The ions take the arrangement that provides the greatest cation‑anion attraction while minimizing the anion‑anion and cation‑cation repulsions. Each
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  • Fall '06
  • Mark
  • Atom, atoms, Chemical bond

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