Nonmetallic elements general properties

The effect of the structure of the positive ion in acids has already been discussed Zn(OH)2 is weaker than Mg(OH)2, while Ag(OH) is weaker than NaOH, etc. Comparing C120, which is weakly acid, with Na20, one would certainly expect it to have basic properties, but the fact that it is weakly acid is probably associated with the exceptional structure of the ion. Again, it must be remembered that, in general, the properties of the oxides of the nonmetallic elements do not fall into line, and CO, NsO, NO and F20 have neither basic not acidic properties. This proves that they are not composed of ions, which naturally raises doubts as to whether the peculiar properties of C120 could not be ascribed to this fact. 

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. 

Arsenic is historically the poison of choice for many murders, both in fiction and reality (e.g., Christie 1924 CNN 1998). The element is considered a metalloid (having both metallic and nonmetallic properties) and is widely distributed in the earth s crust. Arsenic occurs in trace quantities in all rock, soil, water, and air (WHO 2001). Under reducing conditions, arsenite (As ") is the dominant form, while arsenate (As ) generally is the stable form in oxygenated environments. Arsenic salts exhibit a wide range of solubilities, depending on pH and the ionic environment. 

Figure 9.1 A general comparison of metals and nonmetals. A, The positions of metals, nonmetals, and metalloids within the periodic table. B, The relative magnitudes of some key atomic properties vary from left to right within a period and correlate with whether an element is metallic or nonmetallic.

Ceramics can be defined as heat-resistant, nonmetallic, inorganic sofids that are (generally) made up of compounds formed from metalfic and nonmetalfic elements. Although different types of ceramics can have very different properties, in general ceramics are corrosion-resistant and hard, but britde. Most ceramics are also good insulators and can withstand high temperatures. These properties have led to their use in virtually every aspect of modern life. 

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. 

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