Ionic compound containing polyatomic ions

Ionic compounds containing polyatomic ions. Ftitassium dichromate (KjCtjOj, orange), potassium permanganate (KMnOa, very dark purple), and potassium nitrate (KNO3. white). 

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. 

Compounds that contain polyatomic ions Many ionic compounds contain polyatomic ions, which are ions made up of more than one atom. Table 8-6 lists the formulas and the charges for several polyatomic ions. 

Polyatomic Ions Covalent Bonds Within Ions Many ionic compounds contain polyatomic ions, which consist of two or more atoms bonded covalently and have a net positive or negative charge. For example, the ionic compound calcium carbonate is an array of polyatomic carbonate anions and monatomic calcium cations attracted to each other. The carbonate ion consists of a carbon atom covalently bonded to three oxygen atoms, and two additional electrons give the ion its 2- charge (Figure 2.15). In many reactions, a polyatomic ion stays together as a unit. 

Ionic compounds containing polyatomic ions are not binary compounds, because they contain more than two elements. 

Naming ionic compounds containing polyatomic ions follows rules similar to those for naming binary compounds. 

Formulas for polyatomic ionic compounds Many ionic compounds contain polyatomic ions, which are ions made up of more than one atom. Table 7.9 and Figure 7.10 list the formulas and charges of common polyatomic ions. Also, refer to Table R-6 on page 970. A polyatomic ion acts as an individual ion in a compound and that its charge applies to the entire group of atoms. Thus, the formula for a polyatomic compound follows the same rules used for a binary compound. 

When ionic compounds containing polyatomic ions dissolve in water, the polyatomic ions usually dissolve as intact units. 

Many ionic compounds contain polyatomic ions. Table 2.5 shows some common polyatomic ions. Remember that the polyatomic ion stays together as a charged unit. The formula for potassium nitrate is KNO3 each K+ balances one NO3. The formula for sodium carbonate is Na2C03 two Na+ balance one CO. When two or more of the same polyatomic ion are present in the formula unit, that ion appears in parentheses with the subscript written outside. For example, calcium nitrate contains one Ca + and two N03 ions and has the formula Ca(N03)2. Parentheses and a subscript are only used if more than one of a given polyatomic ion is present thus, sodium nitrate is NaN03, not Na(N03). 

Determining Names and Formulas of Ionic Compounds Containing Polyatomic Ions... 

When naming ionic compounds containing polyatomic ions, we write the positive ion, usually a metal, first, and then we write the name of the polyatomic ion. It is important that you learn to recognize the polyatomic ion in the formula and name it correctly. As with other ionic compounds, no prefixes are used. 

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