Group 15 elements metallic-nonmetallic character

As mentioned in our assessment of the metallic-nonmetallic character of the group 15 elements, the oxides of nitrogen are acidic, and they react with water to give acidic solutions. For example, the reaction of N2O5 and H2O yields HNO3, as shown below, and thus N2O5 is the acid anhydride of HNO3. 

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. 

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. 

Recall from Chapter 7 that elements in the same group (vertical column) of the periodic table have the same number of valence electrons, and because of this, they have similar properties. But elements in a period (horizontal row) have properties different from one another. This is because the number of valence electrons increases from one to eight as you move from left to right in any row of the periodic table except the first. As a result, the character of the elements changes. Figure 8.1 illustrates the main group elements and shows that each period begins with two or more metallic elements, which are followed by one or two metalloids. The metalloids are followed by nonmetallic elements, and every period ends with a noble gas. 

In the following brief descriptions of the main-group elements, we will note the metallic—nonmetallic behavior of the elements, as well as the basic—acidic character of the oxides. Although elements in a given group are expected to be similar, the degree of... 

The metallic elements in Group 3A also form many molecular compounds. For example, aluminum reacts with hydrogen to form AIH3, which has properties similar to those of BeH2. The progression of properties across the second row of the periodic table illustrates the gradual shift from metallic to nonmetallic character in the main group elements. 

The elements show increasing metallic character down the group (Table 14.6). Carbon has definite nonmetallic properties it forms covalent compounds with nonmetals and ionic compounds with metals. The oxides of carbon and silicon are acidic. Germanium is a typical metalloid in that it exhibits metallic or nonmetallic properties according to the other element present in the compound. Tin and, even more so, lead have definite metallic properties. However, even though tin is classified as a metal, it is not far from the metalloids in the periodic table, and it does have some amphoteric properties. For example, tin reacts with both hot concentrated hydrochloric acid and hot alkali ... 

The elements show increasing metallic character down the group (Table 14.12). Carbon has definite nonmetallic properties it forms covalent compounds with nonmetals and ionic compounds with metals. The oxides of carbon and silicon are acidic. Germanium is a typical metalloid... 

The most metallic element is francium at the bottom left of the table. The most nonmetallic element is fluorine. The metallic character of elements within a group increases with period number. This means that within a column, the more metallic elements are at the bottom. The metallic character of elements within a period decreases with the increase in group number. This means that within a row, the more metallic elements are on the left. 

There is no more striking example of an enormous discontinuity in general properties between the first- and the second-row elements followed by a relatively smooth change toward more metallic character thereafter than in Group 14. Little of the chemistry of silicon can be inferred from that of carbon. Carbon is strictly nonmetal-lic silicon is essentially nonmetallic germanium is metalloid tin and especially lead are metallic. Some properties of the elements are given in Table 8-1. 

The group shows the normal property of a trend toward metallic character as it is descended. Selenium, tellurium, and polonium have metallic allotropes, and polonium has generally metalloid-type properties where it has been possible to study these (Po is very rare). All the elements combine with a large number of other elements, both metallic and nonmetallic, but in contrast to compounds of the halogens they are more generally insoluble in water, and even when soluble do not ionize readily. 

As we proceed down group 6A, there is a change from nonmetallic to metallic character. Oxygen, sulfur, and selenium are typical nonmetals. Tellurium has some metallic properties and is classified as a metalloid. Polonium, which is radioactive and quite rare, is a metal. Oxygen is a colorless gas at room temperature all of the others are solids. Some of tiie physical properties of tiie group 6A elements are given in Table 7.6 T. 

The variation in properties among the elements of group 5A is more striking than that seen in groups 6A and 7A. Nitrogen at the one extreme exists as a gaseous diatomic molecule it is clearly nonmetallic in character. At the other extreme, bismuth is a reddish white, metallic-looking substance that has most of the characteristics of a metal. 

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