Ionic polyatomic ions

So far, there have been few published simulation studies of room-temperature ionic liquids, although a number of groups have started programs in this area. Simulations of molecular liquids have been common for thirty years and have proven important in clarifying our understanding of molecular motion, local stmcture and thermodynamics of neat liquids, solutions and more complex systems at the molecular level [1 ]. There have also been many simulations of molten salts with atomic ions [5]. Room-temperature ionic liquids have polyatomic ions and so combine properties of both molecular liquids and simple molten salts. 

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

Similar relationships hold for ionic solids containing polyatomic ions (Table 2.2) or transition metal cations (Figure 4.2). 

Distinguish between each of the following pairs (a) an ion and an ionic bond, (b) an ion and a free atom, (c) a covalent bond and an ionic bond, (cl) a triple bond and three single bonds on the same atom, (e) a polyatomic molecule and a polyatomic ion. 

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 bonding results from electrostatic interactions between ions, which can be formed by the transfer of one or more electrons from a metal to a nonmetal or group of nonmetals (forming a polyatomic ion, like N03 ). Covalent bonding, on the other hand, results from sharing one or more electron pairs between two nonmetal atoms. 

NH4)2S04 is an ionic solid composed of covalently bonded polyatomic ions both obey the octet rule ... 

This polyatomic ion (type AB6), like (c), does not obey the octet rule without modification since 12 electrons must be shared to form 6 Sb-F bonds. Sb is a 5 A element, but the charge on the ion gives an extra electron which participates in bonding. The Lewis formula predicts 6 electron groups around the central Sb atom and an octahedral electronic geometry. There are no lone pairs on the Sb atom, so the ionic geometry is the same as the electronic geometry (Section 8-12). 

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). 

Table 13 gives the three contributions to AGhydration for five polyatomic ions, as computed by the PCM technique of Barone et al.,95 using their radii. As mentioned earlier, Gelectrostetic, Gcavitatlon and Gvdw are generally of the same order of magnitude for molecular solutes (Table 8) however this is not true for ionic ones, as can be seen in Table 13. Geiectrostatic is now often an order of magnitude larger.

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. 

When writing the Lewis structures of polyatomic ions, don t forget to show their ionic charge. 

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... 

Ionic bonding may also involve polyatomic ions. The polyatomic ion(s) simply replace(s) one or both of the monoatomic ions. 

Ionic bonds can also result from the interaction of polyatomic ions. 

Oxidation numbers are just a bookkeeping method used to keep track of electron transfers. In a covalent molecule or a polyatomic ion, the oxidation number of each element does not represent an ionic charge, because the elements are not present as ions. However, to assign oxidation numbers to the elements in a covalent molecule or polyatomic ion, you can pretendthe bonds are ionic. 

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. 

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