The nonmetals

The nonmetals (Table 2.5) that have been studied are remarkably uniform in their inability to bind positrons, and their ability to bind positronium (boron is an exception-it apparently does not bind positronium). There is a strong correlation between the Ps-atom and H-atom bond strengths for these atoms, and this correlation extends to almost all examples of positronium binding shown in this chapter. 

QMC methods have proven to be the most powerful for these systems, which have too many particles to be amenable to attack by SVM. 

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The essential operations of an extractive metallurgy flow sheet are the decomposition of a metallic compound to yield the metal followed by the physical separation of the reduced metal from the residue. This is usually achieved by a simple reduction or by controlled oxidation of the nonmetal and simultaneous reduction of the metal. This may be accompHshed by the matte smelting and converting processes. 

In a simple pyrometaHurgical reduction, the reduciag agent, R, combines with the nonmetal, X, ia the metallic compound, MX, according to a substitution reaction of the foUowiag type ... 

Of the halogens, only fluorine attacks siUca readily, forming SiF and O2. A number of halogen compounds of the nonmetals and metalloids react more or less readily with siUca, forming volatile siUcon halogen compounds (Table 1). The formation of SiCl by direct chlorination of mixtures of siUca and carbon is of some technical importance. 

Nonmetal haUdes are generally hydroly2ed to a hydrogen haUde and to an oxy-acid containing the other element. The first row nonmetal haUdes, eg, CCI4, resist hydrolysis because the nonmetal element cannot expand its octet of electrons to form a bond to water before its bond to the haUde is broken. Hydrolysis requires either an energetic water molecule to strike the haUde or ioni2ation of the covalent nonmetal—halide bond, processes that tend to be quite slow (16). 

Periodic table. The group numbers stand above the columns. The numbers at the left of the rows are the period numbers. The black line separates the metals from the nonmetals. [Note A complete periodic table is given inside the front cover.)... 

Nonmetal atoms form negative ions (anions—pronounced AN-i-ons) by gaining electrons. Consider, for example, what happens when atoms of the nonmetals chlorine and oxygen acquire electrons ... 

When a metal such as sodium (Na) or calcium (Ca) reacts with a nonmetal such as chlorine (Cl2), the product is ordinarily an ionic compound. The formula of that compound (e.g., NaCl, CaCl2) shows the simplest ratio between cation and anion (one Na+ ion for one Cl ion one Ca2+ ion for two Cl- ions). In that sense, the formulas of ionic compounds are simplest formulas. Notice that the symbol of the metal (Na, Ca) always appears first in the formula, followed by that of the nonmetal. 

Monatomic anions are named by adding the suffix -ide to the stem of the name of the nonmetal from which they are derived. 

Click Coached Problems for a self-study module on naming compounds of the nonmetals. 

Many of the best-known binary compounds of the nonmetals have acquired common names. These are widely—and in some cases exclusively—used. Examples include... 

This half-reaction occurs when the anion cannot be oxidized. Examples include nitrate and sulfate anions, where the nonmetal present is already in its highest oxidation state (+5 for N, +6 for S). 

Table 21.1 (p. 556) lists some of the properties of the eight nonmetals considered in this chapter. Notice that all of these elements are molecular those of low molar mass (N2> 02, F2> Cl2) are gases at room temperature and atmospheric pressure (Figure 21.2, p. 556). Stronger dispersion forces cause the nonmetals of higher molar mass to be either liquids (Br2) or solids (I2, P4. S8). 

Table 21.2 lists some of the more important hydrogen compounds of the nonmetals. (Those of carbon are discussed in Chapter 22.) The physical states listed are those observed at 25°C and 1 atm. The remainder of this section is devoted to a discussion of the chemical properties of the compounds shown in boldface in die table. 

Table 21.4 lists some of the more important oxoacids of the nonmetals. In all these compounds, the ionizable hydrogen atoms are bonded to oxygen, not to the central nonmetal atom. Dissociation of one or more protons from the oxoacid gives the corresponding oxoan-ion (Figure 21.8, p. 567). 

These trends are general ones, observed with other oxoadds of the nonmetals. Recall, for example, that nitric acid, HNO3 (oxid. no. N = +5), is a strong acid, completely ionized in water. In contrast, nitrous add, HN02 (oxid. no. N = +3), is a weak acid (Ka = 6.0 X 10-4). The electronegativity effect shows up with the strengths of the oxoadds of sulfur and selenium ... 

The metals are found toward the left side of the periodic table and the nonmetals are at the right side. A compound containing elements from the opposite sides of the periodic table can be expected to form a conducting solution when dissolved in water. Notice from our examples that hydrogen reacts with nonmetals to form compounds that give conducting solutions in water. In this sense, hydrogen acts like a metallic element. 

The elements that form network solids lie on the right side of the periodic table, bordering the elements that form molecular crystals on one side and those that form metals on the other. Thus they are intermediate between the metals and the nonmetals. In this borderline region classifications are sometimes difficult. Whereas one property may suggest one classification, another property may lead to a different conclusion. Figure 17-3 shows some elements that form solids that are neither wholly metallic nor wholly molecular crystals. 

The location of the metals in the periodic table is shown in Figure 17-4. We see that the metals are located on the left side of the table, while the nonmetals are exclusively in the upper right corner. Furthermore, the elements on the left side of the table have relatively low ionization energies. We shall see that the low ionization energies of the metallic elements aid in explaining many of the features of metallic behavior. 

A malleable substance (from rhe Latin word for hammer ) is one that can be hammered into thin sheets (Fig. B. 11). A ductile substance (from the Latin word for drawing out ) is one that can be drawn out into wires. Copper, for example, is a metal. It conducts electricity, has a luster when polished, and is malleable. It is so ductile that it is readily drawn out to form electrical wires. Sulfur, on the other hand, is a nonmetal. This brittle yellow solid does not conduct electricity, cannot be hammered into thin sheets, and cannot be drawn out into wires. The distinctions between metals and metalloids and between metalloids and nonmetals are not very precise (and not always made), but the metalloids are often taken to be the seven elements shown in Fig. B.12 on a diagonal band between the metals on the left and the nonmetals on the right. 

FIGURE C.7 The typical monatomic anions formed by a selection of elements in the periodic table. Notice how the charge on each ion depends on its group number. Only the nonmetals form monatomic anions under common conditions. 

First check to see whether the compounds are ionic or molecular. Many compounds that contain a metal are ionic. Write the symbol of the metal first, followed by the symbol of the nonmetal. The charges on the ions are determined as shown in Examples C.l and C.2. Subscripts are chosen to balance charges. Compounds of two nonmetals are normally molecular. Write their formulas by listing the symbols of the elements in the same order as in the name, with subscripts corresponding to the Greek prefixes used. 

The elements at the upper right of the periodic table have high ionization energies so they do not readily lose electrons and are therefore not metals. Note that our knowledge of electronic structure has helped us to understand a major feature of the periodic table—in this case, why the metals are found toward the lower left and the nonmetals are found toward the upper right. 

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