Question 3.10: Applying Various Rules for Naming Compounds Name the compoun...
Applying Various Rules for Naming Compounds
Name the compounds (a) CuCl_{2}; (b) ClO_{2}; (c) HIO_{4}; (d) Ca{(H_{2}PO_{4})}_{2}.
Analyze
CuCl_{2} and Ca{(H_{2}PO_{4})}_{2} are ionic compounds. To name these compounds, we must identify and name the ions. ClO_{2} and HIO_{4} are molecular compounds. ClO_{2} is a binary compound of two nonmetals and HIO_{4} is an oxoacid.
(a) In this compound, the oxidation state of Cu is +2. Because Cu can also exist in the oxidation state of +1, we must clearly distinguish between the two possible chlorides. CuCl_{2} is copper(II) chloride.
(b) Both Cl and O are nonmetals. ClO_{2} is a binary molecular compound called chlorine dioxide.
(c) The oxidation state of I is +7. By analogy to the chlorine-containing oxoacids in Table 3.6, we should name this compound periodic acid (pronounced “purr-eye-oh-dic “acid).
| TABLE 3.6 Nomenclature of Some Oxoacids and Their Salts | ||||
| Oxidation State | Formula of Acid^{a} | Name of Acid^{b} | Formula of Salt^{b} | Name of Salt |
| Cl: +1 | HClO | Hypochlorous acid | NaClO | Sodium hypochlorite |
| Cl: +3 | HClO_{2} | Chlorous acid | NaClO_{2} | Sodium chlorite |
| Cl: +5 | HClO_{3} | Chloric acid | NaClO_{3} | Sodium chlorate |
| Cl: +7 | HClO_{4} | Perchloric acid | NaClO_{4} | Sodium perchlorate |
| N: +3 | HNO_{2} | Nitrous acid | NaNO_{2} | Sodium nitrite |
| N: +5 | HNO_{3} | Nitric acid | NaNO_{3} | Sodium nitrate |
| S: +4 | H_{2}SO_{3} | Sulfurous acid | {Na}_{2}SO_{3} | Sodium sulfite |
| S: +6 | H_{2}SO_{4} | Sulfuric acid | {Na}_{2}SO_{4} | Sodium sulfate |
_{}^{a}\textrm{In} all these acids, H atoms are bonded to O atoms, not the central nonmetal atom. Often formulas are written to reflect this fact, for instance, HOCl instead of HClO and HOClO instead of HClO_2.
_{}^{b}\textrm{In} general, the -ic and -ate names are assigned to compounds in which the central nonmetal atom has an oxidation state equal to the periodic table group number minus 10. Halogen compounds are exceptional in that the -ic and -ate names are assigned to compounds in which the halogen has an oxidation state of +5 (even though the group number is 17).
(d) The polyatomic anion H_{2}{PO_{4}}^{-} is dihydrogen phosphate ion. Two of these ions are present for every Ca^{2+} ion in the compound calcium dihydrogen phosphate.
Assess
A fair bit of memorization is associated with naming compounds correctly. Mastery of this subject usually requires a lot of practice.