Nonmetallic character

Metals typically form basic oxides and nonmetals typically form acidic oxides, but what about the elements that lie on the diagonal frontier between the metals and nonmetals Along this frontier from beryllium to polonium, metallic character blends into nonmetallic character, and the oxides of these elements have both acidic and basic character (Fig. 10.7). Substances that react with both acids and bases are classified as amphoteric, from the Greek word for both. For example, aluminum oxide, A1203, is amphoteric. It reacts with acids ... 

The valence electron configuration of the atoms of the Group 2 elements is ns1. The second ionization energy is low enough to be recovered from the lattice enthalpy (Fig. 14.18). Flence, the Group 2 elements occur with an oxidation number of +2, as the cation M2+, in all their compounds. Apart from a tendency toward nonmetallic character in beryllium, the elements have all the chemical characteristics of metals, such as forming basic oxides and hydroxides. 

Beryllium shows a hint of nonmetallic character, but the other Group 2 elements... 

Boron oxide is an add anhydride. Aluminum shows some nonmetallic character in that its oxide is amphoteric. 

What Are the Key Ideas As in Chapter 1.4, the key idea is that the elements show a periodicity in their physical and chemical properties, with nonmetallic character becoming more pronounced toward the right of the periodic table. 

In addition to the types of compounds discussed so far, the group IVA elements also form several other interesting compounds. Silicon has enough nonmetallic character that it reacts with many metals to form binary silicides. Some of these compounds can be considered as alloys of silicon and the metal that result in formulas such as Mo3Si and TiSi2. The presence of Si22 ions is indicated by a Si-Si distance that is virtually identical to that found in the element, which has the diamond structure. Calcium carbide contains the C22-, so it is an acetylide that is analogous to the silicon compounds. 

Rb > Ca > Sc> Fe > Te > Br > O > F The difficulty in establishing this series is in placing the elements Te and Br. First, the metal Fe is more metallic than the nonmetal Te. Further, Te clearly is more metallic than the halogen Br. Finally, we only need to recognize that Cl and O have approximately the same nonmetallic character, and Br clearly is more metallic than is Cl. 

In earlier chapters, we saw examples of how the metallic or nonmetallic character of an element affects its chemistry. Metals tend to form ionic compounds with nonmetals, whereas nonmetals tend to form covalent, molecular compounds with one another. Thus, binary metallic hydrides, such as NaH and CaH2, are ionic solids with high melting points, and binary nonmetallic hydrides, such as CH4, NH3, H20, and HF, are covalent, molecular compounds that exist at room temperature as gases or volatile liquids (Section 14.5). 

Oxides exhibit similar trends. In the third row, for example, Na20 and MgO are typical high-melting, ionic solids, and P4O10, S03, and C1207 are volatile, covalent, molecular compounds (Section 14.9). The metallic or nonmetallic character of an oxide also affects its acid-base properties. Na20 and MgO are basic, for example,... 

PROBLEM 19.1 Predict which element in each of the following pairs has more nonmetallic character ... 

Figure 6. The occurrence of metallic vs nonmetallic character in the periodic table of the elements the variation of R/V for naturally occurring elements of the s, p, and d blocks (adapted from Edwards and Sienko27).

Nonmetallic character decreases from top to bottom and increases from left to right in the periodic table. 

Molecular (acidic) character of oxides increases as nonmetallic character of the element that is combined with oxygen increases (see Figure 6-8). 

Compare the stracmres of the dioxides of sulfur, selenium, tellurium, and polonium. How do they relate to the metallic or nonmetallic character of these elements ... 

While metallic compounds are generally formed by the combination of a metal with a metal, they can sometimes be formed in the combination of a metal with a nonmetal. This occurs in circumstances where the influence of the metal can predominate over the influence of the nomnetal, namely (i) when the ratio of metal atoms to nomnetal atoms is relatively high, (ii) when the nonmetallic character of the nonmetal is relatively weak, or (iii) when both circumstances pertain. 

Consider the elements Be, C, Cl, Sb, and Cs. Select the element that (a) has the lowest electronegativity (b) has the greatest nonmetallic character (c) is most likely to participate in extensive tt bonding (d) is most likely to be a metalloid. 

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