Names and Charges of Polyatomic Ions

Acetate, CH3COO- Carbonate, C03 Arsenate, As04 Hexacyanoferrate(ll), 

Astatate, At03 Dichromate, Cr207 Borate, BOg Orthosilicate, 104  

N3 Hexachioropiatinate, Citrate, CgHg07 Diphosphate, P2O7  

Formate, HCOO Ruthenate, Ru04 Ammonium, NH4+ Mercury(l), Hg2 + 

Hydroxide, OH Seienate, Se04 Neptunyl(V), Np02+ NeptunyKVI), NpOg  

---

Symbols and Abbreviations The Modern Periodic Table Alphabetical Table of the Elements Properties of Elements Electron Configurations of the Elements Useful Physical Constants Names and Charges of Polyatomic Ions Solubility Guidelines Solubility Product Constants Acid-Base Indicators... 

The names and charges of polyatomic ions must be memorized. They are an important part of the vocabulary of chemistry. 

Polyatomic Ions Polyatomic ions are ions that have many atoms bonded together. It is best to become familiar with the names and charges of these compounds. A listing can be found in the reference tables in Appendix 4 in the back of this book. An example of a polyatomic ion that has been presented earlier in this chapter is NH41+, the ammonium ion. The compound NH4C1 would be called ammonium chloride. 

There are many different polyatomic anions, including several that are abundant in nature. Each is a stable chemical species that maintains its stmcture in the solid state and in aqueous solution. Polyatomic anions are treated as distinct units when writing chemical formulas, naming compounds, or drawing molecular pictures. The names, formulas, and charges of the more common polyatomic anions are listed in Table 3-4. You should memorize the common polyatomic ions because they appear regularly throughout this textbook. 

You will also need to learn the names, formulas, and charges of the following polyatomic ions ... 

When you write a chemical formula that involves polyatomic ions, you treat them just like other ions. You still need to balance charges to form a neutral atom. We re sorry to report that when you re converting from a formula to a name, you can t use any simple rule for naming polyatomic ions. You just have to memorize the entire table of polyatomic ions and their charges. 

Ionic compounds containing polyatomic ions (Section 2.8) are named in the same way as binary ionic compounds First the cation is identified and then the anion. For example, Ba(N03)2 is called barium nitrate because Ba2+ is the cation and the N03 polyatomic anion has the name nitrate. Unfortunately, there is no systematic way of naming the polyatomic ions themselves, so it s necessary to memorize the names, formulas, and charges of the most common ones listed in Table 2.3. The ammonium ion (NH4+) is the only cation on the list all the others are anions. 

Table 9-1 lists a few of the more commonly encountered polyatomic ions, their formulas, names, and charges. These should be memorized. 

We emphasize at this point that it is essential to learn the name, composition, and charge of each of the common polyatomic anions (and the cation). If you do not recognize these ions by formula and by name, you will not be able to write the compound s name when given its formula or the compound s formula when given its name. You must also learn the names of the common acids. 

Naming ionic compounds that contain polyatomic ions is very similar to naming binary ionic compounds. For example, the compound NaOH is called sodium hydroxide, because it contains the Na (sodium) cation and the OH" (hydroxide) anion. To name these compounds, you must learn to recognize the common polyatomic ions. That is, you must learn the composition and charge of each of the ions in Table 5.4. Then when you see the formula NH4C2H3O2, you should immediately recognize its two "parts" ... 

The names and formulas of some common cations are shown in TABLE 2.4 and on the back inside cover of the text. The ions on the left side in Table 2.4 are the monatomic ions that do not have more than one possible charge. Those on the right side are either polyatomic cations or cations with more than one possible charge. The Hg2 ion is unusual because, even though it is a metal ion, it is not monatomic. It is called the mercury(I) ion because it can be thought of as two Hg+ ions bound together. The cations that you will encounter most frequently are shown in boldface. You should learn these cations first. 

Atoms of two or more elements can also combine to form a polyatomic ion, a chemically distinct species with an electric charge. Communication in the world of chemistry and understanding many applications require one to know the names, formulas, and charges of the common polyatomic ions listed in Table 5.1. 

TABLE 6.6 Names, Formulas, and Charges of Some Common Polyatomic Ions... 

Determine the chemical formulas for barium sulfate, magnesium nitrate, and sodium acetate. Each compound contains a monatomic cation and a polyatomic anion. What are the names and electrical charges of these ions ... 

As we saw previously, some ionic compormds contain polyatomic ions (ions that are themselves composed of a group of atoms with an overall charge). The most common polyatomic ions are listed in Table 5.6. We name ionic compormds containing polyatomic ions using the same procedure we apply to other ionic compormds, except that we use the name of the polyatomic ion whenever it occurs. For example, KNO3 is named using its cation, K" ", potassium, and its polyatomic anion, NOs , nitrate. The full name is potassium nitrate. 

Oxyacids are acids that contain oxyanions, which can be found in the table of polyatomic ions (Table 5.6). For example, HNO3 (aq) contains the nitrate (NOs ) ion, H2S03(flq ) contains the sulfite (S03 ) ion, and H2SO4 (aq) contains the sulfate (SO/ ) ion. All of these acids are a combination of one or more ions with an oxyanion. The number of H ions depends on the charge of the oxyanion, so that the formula is always charge-neutral. The names of oxyacids depend on the ending of the oxyanion ( Figure 5.15). 

Ions that consist of a combination of two or more atoms are called polyatomic ions. Because these ions are commonly encountered in general chemistry, you must know the names, formulas, and charges of the polyatomic ions listed in Table 2.9. Although most of the coimnon polyatomic ions are anions, a few are cations. 

Table 2.2 lists some of the polyatomic ions that you will need to know, along with their names and charges. Notice that... 

---