Polyatomic ions bonding within

The compounds described in Example 10-2 are binaty ionic compounds consisting of monatomic cations and monatomic anions. Commonly encountered ternary ionic compounds consist of monatomic and polyatomic ions. Bonding between atoms within the polyatomic ions is covalent. Some ternary ionic compounds are considered later in the chapter. 

Force Within Unit (Intra) covalent bond within polyatomic ion — — covalent bond... 

Force within units Covalent bond within polyatomic ion Atomic forces between subatomic particles Atomic forces between subatomic particles Covalent bond... 

Polyatomic ions are discussed in the section on covalent bonding because the bonding within these ions is covalent. 

Intermolecular forces must be distinguished from chemical bonds. Intermolecular forces are the forces between molecules chemical bonds are the bonds within molecules (and polyatomic ions) and between ions. 

The bonding within these polyatomic cations is weak. One can readily calculate bond orders which are small fiactions. There is no suggestion that any of these cations would be stable outside the zeolite, nor that their geometries are as rigid as those of molecules or molecular ions. All of these polyatomic cations conform to the electrostatic requirements of the zeolite framework, somewhat as liquids adopt the shapes of their containers. Perhaps it is reasonable, because the bonding is so weak, not to refer to these as polyatomic cations at all, but rather as electron traps. This more physical description is consistent with the observation that some of these clusters can be prepared (in low concentration) by y-... 

The polyatomic ions you learned about in Chapter 8 are related to covalent compounds. Although the unit acts as an ion, the atoms within the ion itself are covalently bonded. The structures of these ions can also be represented by Lewis structures. 

Polyatomic ions, such as hydroxide (left), sulfate (center), and oxalate (right), are composed of more than one atom. Electrons are shared between the atoms within the ion, forming covalent bonds, but the ion as a whole has a charge. Thus, polyatomic ions form ionic bonds with other ions to produce ionic compounds. 

The formulas of the chemical compounds are no accident. There is an NaCl, but no NaCl2 there is a Cap2, but no CaF. On the other hand, certain pairs of elements form two, or even more, different compounds, e.g. C]u20, CuO N2O, NO, NO2. In the case of ionic compounds the relative number of positive and negative ions in a formula is governed simply by the rule of electrical neutrality. In covalent compounds, or within polyatomic ions (like NO ), structures are formed by covalent bonds (i.e., electron sharing). A hierarchy of covalent bonding theories exists, of which the simplest, the drawing of Lewis structures, is emphasized in this and in most elementary texts. 

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. 

Another complication in identifying ionic compounds is that many substances contain polyatomic ions. For example, NFI4CI contains NH4 and Cr ions, and Na2S04 contains Na and S04 ions. The bonds within the ammonium and sulfate ions are covalent bonds. 

The bonding between the atoms within polyatomic ions is just like the bonding within molecular compounds (Section 5.3), but the group of atoms has either more or fewer electrons than protons and therefore has an overall charge. Compounds that contain polyatomic ions are ionic, and their formulas are written by the same procedure described for binary ionic compounds. The only difference is that the polyatomic ion formula is enclosed in parentheses when more than one such ion is present. For example, the formula of aluminum nitrate is Al(NOg)g. The compounds are also named in the same manner as binary ionic compounds, with the... 

The covalent bonding within a polyatomic ion such as NH4+ or S04 is very strong, but the forces that hold the entire substance together are ionic.Thus a compound that contains a polyatomic ion is an ionic compound (see Section 7-12). 

Ionic crystals are not limited to monatomic ions polyatomic ions—ions consisting of two or more atoms—also form crystal structures. Atoms within a polyatomic ion are held together by covalent bonds (Section 12.3). Figure 12.3 is a model of a calcium carbonate crystal. The formula of a carbonate ion, one of which is circled in Figure 12.3, is The carbon atom is surrounded by three covalently bonded... 

In an equation for dissociation, the charges must balance. For example, magnesium nitrate dissociates to give one magnesium ion for every two nitrate ions. However, only the ionic bonds between Mg + and NO3 are broken the covalent bonds within the polyatomic ion are retained. The dissociation for Mg(N03)2 is written as follows ... 

Although most drugs are molecular compounds, a number of ionic compounds have medical uses. Consider the following partial list of ionic compounds used in medicine. Notice that many of these compounds contain polyatomic ions. The bonding between a metal and a polyatomic ion is ionic. However, the bonding within a polyatomic ion is covalent, the topic of our next section. 

A.2.2 Nonpolar Binary Intermetallic Phases. Zintl phases are characterized by the presence of markedly heteropolar bonding between the Zintl ions (electronegative polyatomic clusters) and the more electropositive metal atoms. By contrast, the bonding between heteronuclear atoms within other intermetallic compounds is primarily covalent or metallic. A number of different structure types exist for any given... 

Covalent bonds in polyatomic molecules and ions are formed by the overlap of hybrid orbitals, or of hybrid orbitals with unhybridized ones. Therefore, the hybridization bonding scheme is still within the framework of valence bond theory electrons in a molecule are assumed to occupy hybrid orbitals of the individual atoms. 

Silicate structures consist of four oxygen atoms bonded to silicon, forming a negatively charged polyatomic anion with a tetrahedral shape. Various metal ions within the structure balance the charge of the compound. 

---