Ionic compounds polyatomic ions

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

Ag2 SO4 The polyatomic sulfate ion indicates that this is an ionic compound. Silver is always +1, so no Roman numeral is needed silver sulfate. 

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... 

Ionic compounds are made up of positively charged ions (usually metal ions) and negatively charged ions (usually non-metal ions or polyatomic anions) held together by electrostatic forces of attraction. Molecular compounds are made up of discrete units called molecules. Generally they consist of a small number of nonmetal atoms held together by covalent bonds (sharing of electrons). 

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). 

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... 

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-... 

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). 

Ionic compounds consist of positive ions (cations) and negative ions (anions) hence, ionic compounds often consist of a metal and nonmetal. The electrostatic attraction between a cation and anion results in an ionic bond that results in compound formation. Binary ionic compounds form from two elements. Sodium chloride (NaCl) and sodium fluoride (NaF) are examples of binary ionic compounds. Three elements can form ternary ionic compounds. Ternary compounds result when polyatomic ions such as carbonate (C032 ), hydroxide (OH-), ammonium (NH4+), form compounds. For example, a calcium ion, Ca2+, combines with the carbonate ion to form the ternary ionic compound calcium carbonate, CaC03. Molecular compounds form discrete molecular units and often consist of a combination of two nonmetals. Compounds such as water (H20), carbon dioxide (C02), and nitric oxide (NO) represent simple binary molecular compounds. Ternary molecular compounds contain three elements. Glucose ( 12 ) is a ternary molecular compound. There are several distinct differences between ionic and molecular compounds, as summarized in Table 1.2. 

The sizes of polyatomic ions such as NH and SO2 are of interest for the understanding of the properties of ionic compounds such as (NH4)2S04, but the experimental difficulties attending their determination exceed those of simple ions. In addition, the problem of constancy of size from one compound to the next—always a problem... 

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. 

Finally, the sum of the oxidation numbers in a neutral compound is 0 the sum of the oxidation numbers in a polyatomic ion (an ion with at least two atoms) is equal to its ionic charge. 

The rules for naming chemical compounds depend on whether the substance is a molecular substance or an ionic substance. Molecular compounds are comprised only of nonmetals. Ionic compounds are almost always comprised of a metal and a nonmetal. If a compound contains one of the polyatomic ions listed in Table 2.1, it is an ionic compound. 

Ternary ionic compounds are ionic compounds containing one or more polyatomic ions. The possible combinations are a monatomic cation bonded to a polyatomic anion, a polyatomic cation bonded to a monatomic anion, or a polyatomic cation bonded to a polyatomic anion. There are additional rules that must be added to the rules in the previous section ... 

You can use valences to write chemical formulas. This method is faster than using Lewis structures to determine chemical formulas. As well, you can use this method for both ionic and covalent compounds. In order to write a chemical formula using valences, you need to know which elements (or polyatomic ions) are in the compound, and their valences. You also need to know how to use the zero sum rule For neutral chemical formulas containing ions, the sum of positive valences plus negative valences of the atoms in a compound must equal zero. 

Solution The first two ions are single atom anions and are called sulfide and nitride. The next two are binary ionic compounds, calcium fluoride and potassium sulfide. The polyatomic ions hydroxide and sulfate are present in sodium hydroxide and sodium sulfate. Finally, the last two compounds are covalently bonded and are called sulfur trioxide and carbon tetrachloride. 

Finally, use the lowest ratio of subscripts if the compound is ionic, MgCl2. The crisscross method also works for compounds containing polyatomic ions. One note of caution, however when there are multiple units of a polyatomic ion present, you must use parentheses to indicate this fact. Using this... 

To name an ionic compound, name the cation first and then the anion. Use just the name of the element for monatomic cations of elements that form only one cation. For monatomic cations of elements that can form more than one cation, indicated the charge on the cation by a Roman numeral in parentheses added to the name of the element. Polyatomic cations have special names, ammonium ion being the most important. 

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