Compound polyatomic ions

In addition to the Zachariasen and radius ratio rules, for oxides the electronegativity of the predominant cation should be between 1.7 and 2.1 (7). If the cation electronegativity is too high, the compound tends to form molecules or discrete polyatomic ions rather than a connected network. For example, CrO satisfies the radius ratio rule, but the highly electronegative Cr ions promote the formation of discrete dichromate(VI) ions, Cr202 , in the presence of other oxides. 

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

Step 2 If the compound is an oxoacid, derive the name of the acid from the name of the polyatomic ion that it produces, as in Toolbox D.1. In general,... 

U 1 Name ions, binary inorganic compounds, oxoacids, compounds with common polyatomic ions, and hydrates, and write their formulas (Toolboxes D.l and D.2, Self-Test D.l, and Examples D.l, D.2, and D.3). 

When an element is part of a compound or a polyatomic ion, we assign its oxidation number by using the procedure in Toolbox K.l. 

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. 

The charges on polyatomic ions cause ionic bonding between these groups of atoms and oppositely charged ions. In writing electron dot structures, the distinction between ionic and covalent bonds must be clearly indicated. For example, an electron dot diagram for the compound NH4NO, would be... 

Some ionic compounds contain a combination of bonds. For instance, in polyatomic ions such as ammonium (NH4+), the hydrogen atoms are bonded to the nitrogen atom by polar covalent bonds. The ionic bond is thus between this covalently bonded moiety and another oppositely charged ion such as chloride (CT). 

When naming compounds containing species not on these lists, it may help to find a chemical species on the list from the same family or a polyatomic ion that is similar. 

The presence of a polyatomic ion in a compound requires substituting the name of the polyatomic ion for the name of the cation or anion in a comparable mctal/nonmetal compound. We will use no prefixes. 

In Sections 9-3 and 9-4, we will show you two types of chemical bonds ionic and covalent. It is important to be able to represent compounds in terms of the atoms and valence electrons that make up the chemical species (compounds or polyatomic ions). One of the best ways is to use Lewis symbols and structures. 

Ionic bonding is present in compounds containing a metal and a nonmetal or in a compound containing one or more polyatomic ions. There are a few exceptions to this generalization, but these usually do not appear in this type of question. An ionic substance must contain at least two different elements, so we... 

Hint One formula unit of the compound in part (c) contains two identical monatomic ions and one polyatomic ion. 

The names of polyatomic ions may be used directly in compounds that contain... 

As we end this section, let us reconsider ionic radii briefly. Many ionic compounds contain complex or polyatomic ions. Clearly, it is going to be extremely difficult to measure the radii of ions such as ammonium, NH4, or carbonate, COs, for instance. However, Yatsimirskii has devised a method which determines a value of the radius of a polyatomic ion by applying the Kapustinskii equation to lattice energies determined from thermochemical cycles. Such values are called thermochemical radii, and Table 1.17 lists some values. 

Crafting names and formulas for ionic and molecular compounds Handling polyatomic ions Talking about acids... 

To complicate your life further, polyatomic ions sometimes occur multiple times within the same ionic compound. How do you specify that your compound has two sulfate ions in a way that makes visual sense Put the entire polyatomic ion formula in parentheses and then add a subscript outside the parentheses to indicate how many such ions you have, as in (S04 ")2-... 

Ncime the following compounds that contain polyatomic ions ... 

Look up (or recall) the polyatomic ions in each compound, and specify the charge of the cation if it s a metal that can take on different charges. 

Sorry, it s true. Not only are polyatomic ions annoying because you have to memorize them, but they pop up everywhere. If you don t memorize the polyatomic ions, you ll waste time trying to figure out weird (and incorrect) covalent bonding cirrangements when what you re really dealing with is a straightforwcird ionic compound. Here are the common polyatomic ions in Table 22-1 (see Chapter 6 for more information on these ions). 

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