Ammonium nitrate polyatomic ions

Visualize NH4 NO3. (Always think atoms and molecules.) Ammonium and nitrate are common polyatomic ions whose chemical formulas you should remember. 

When a salt containing polyatomic ions dissolves In water, the cations separate from the anions, but each polyatomic ion remains intact. An example Is ammonium nitrate, composed of NH4 polyatomic cations and NO3 polyatomic anions. Ammonium nitrate dissolves In water to give a solution containing NH4 cations and NO3 anions, as Figure 3-21 Illustrates. 

Molecular view of an aqueous solution of ammonium nitrate. Ammonium ions separate from nitrate ions, but both these species remain intact as polyatomic clusters. 

Sometimes groups of atoms may possess a charge and behave as ions. We call these chemical species polyatomic ions. Examples include the ammonium ion, NH4, the nitrate ion, NO, and the bicarbonate ion, HCOf. 

Notice in Table 6-1 that all the common polyatomic ions except ammonium have a negative charge ranging between -1 and -3. You also see a number of -ite/-ate pairs, such as chlorite and chlorate, phosphite and phosphate, and nitrite and nitrate. If you look closely at these pairs, you notice that the only difference between them is the number of oxygen atoms in each ion. Specifically, the -ate ion always has one more oxygen atom than the -ite ion but has the same overall charge. 

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. 

Many compounds contain one or more polyatomic ions. Often these compounds contain three elements, in which case they are called tertiary compounds. Although they are not binary compounds, they still contain one type of anion and one type of cation. The same naming rules that apply to binary compounds apply to these compounds as well. For example, NH4C1 is called ammonium chloride. Na2S04 is called sodium sulfate. NiS04 is called nickel(II) sulfate. NH4N03 is called ammonium nitrate. 

A solid consisting of oppositely charged ions is called an ionic solid, or (often) a salt. Ionic solids can consist of simple ions, as in sodium chloride, or of polyatomic (many-atom) ions, as in ammonium nitrate (NH4N03), which contains ammonium cations (NH4+) and nitrate anions (N03 ). The ball-and-stick models of these ions are shown in Fig. 2.20. 

We have not yet considered ionic compounds that contain polyatomic ions. For example, the compound ammonium nitrate, NH4NO3, contains the polyatomic ions NH4+ and N03. Polyatomic ions are assigned special names that must be memorized to name the compounds containing them. The most important polyatomic ions and their names are listed in Table 2.5. 

When a compound has polyatomic ions, such as those in Figure 7, look for the cations and anions. Formulas can tell you which elements make up polyatomic ions. For example, in the formula KNO3, NO3 is a nitrate ion, NOi. KNO3 does not have a KN" and an O3 ion. Similarly, the formula of ammonium nitrate is written NH4NO3, because NH4 in a formula stands for the ammonium ion, NHj, and NO3 stands for a nitrate ion, NO3. If it were written as H4N2O3, the number of atoms would be correct. However, the formula would no longer clearly show which ions were in the substance and how many there were. The formula NH4NO3 shows that ammonium nitrate is made up of ammonium and nitrate ions in a 1 1 ratio. 

Polyatomic ions are groups of atoms that bear an electric charge. Examples include the ammonium ion, NH4+ the sulfate ion, and the nitrate ion, NOg". Table 2-3... 

Let us point out another aspect of the classification of compounds as ionic or covalent. Not all ions consist of single charged atoms. Many are small groups of atoms that are covalently bonded together, yet they still have excess positive or negative charge. Examples of such.polyatomic ions are ammonium ion, NH4+, sulfate ion, and nitrate ion,... 

Both of these ions are polyatomic ions with names you should memorize. The name ofNH4N03 is ammonium nitrate. 

Convert between the names and chemical formulas for common polyatomic ions such as hydroxide, ammonium, acetate, sulfate, nitrate, phosphate, and carbonate. Be sure to check with your instructor to determine which polyatomic ions you will be expected to know for your exams. 

So far in this chapter we have discussed only binary ionic compounds, which contain ions derived from single atoms. However, many compounds contain polyatomic ions charged species composed of several atoms. For example, ammonium nitrate contains the and N03 ions. 

These ions with their opposite charges attract each other in the same way as do the simple ions in binary ionic compounds. However, the individual polyatomic ions are held together by covalent bonds, with all of the atoms behaving as a unit. For example, in the ammonium ion, NH +, there are four N—H covalent bonds. Likewise, the nitrate ion, N03, contains three covalent N—O bonds. Thus, although ammonium nitrate is an ionic compound because it contains the NH " and N03 ions, it also contains covalent bonds in the individual polyatomic ions. When ammonium nitrate is dissolved in water, it behaves as a strong electrolyte like the binary ionic compounds sodium chloride and potassium bromide. As we saw in Chapter 8, this occurs because when an ionic solid dissolves, the ions are freed to move independently and can conduct an electric current. 

This section has been discussing monoatomic (one atom) ions. But polyatomic (many atom) ions do exist. The ammonium ion, MU, is a polyatomic ion, or, specifically, a polyatomic cation. The nitrate ion, NO3, is also a polyatomic ion, or, specifically, a polyatomic anion. 

If the compound contains botir a polyatomic cation and a polyatomic anion, use the names of both polyatomic ions. For example, NH4NO3 is ammonium nitrate. 

Indicate, on the basis of general principles, whether or not the following polyatomic ions are colored, (a) Nitrate, NO3 (b) Permanganate, Mn04 (c) Ammonium, NH4. ... 

Polyatomic ions, such as sulfate, nitrate, ammonium and phosphate, must be quantified by other methods such as ion chromatography (IC). Ion analysis methods require filters to be extracted in deionized distilled water and then filtered to remove the insoluble residue. The extraction volume needs to be as small as possible, lest the solution become too dilute to detect the desired constituents (Table 4.2). 

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