Nonmetallic Elements and Their Compounds

The nose cone of the space shuttle is made of graphite and silicon carbide and can withstand the tremendons heat generated when the vehicle enters Earth s atmosphere. The models show graphite and sihcon carbide, which has a diamond stmctnre. 

Of the 117 elements known, only 25 are nonmetallic elements. Unlike the metals, the chemistry of these elements is diverse. Despite their relatively small number, most of the essential elements in biological systems are nonmetals (H, C, N, P, O, S, Cl, and I). This group of nonmetallic elements also includes the most unreactive of the elements—the noble gases. The unique properties of hydrogen set it aside from the rest of the elements in the periodic table. A whole branch of chemistry—organic chemistry—is based on carbon compounds. 

In this chapter, we continue our survey of the elements by concentrating on the nonmetals. The emphasis will again be on important chemical properties and on the roles of nonmetals and their compounds in industrial, chemical, and biological processes. 

Recall that there is no totally suitable position for hydrogen in the periodic table. 

Properties of nonmetals are more varied than those of metals. A number of nonmetals are gases in the elemental state hydrogen, oxygen, nitrogen, fluorine, chlorine, and the noble gases. Only one, bromine, is a liquid. All the remaining nomnetals are solids at room temperature. Unlike metals, nonmetaUic elements are poor conductors of heat and electricity they exhibit both positive and negative oxidation numbers. 

Arsenic is a metalloid. The metalloids and the nonmetallic elements and their compounds exhibit chemistry that varies considerably. 

In This Chapter, You Will Learn some of the properties of metalloids and nonmetals and which compounds th form.  

Arsenic, the poison of many murder mysteries, can cause severe abdominal pain, intense thirst, vomiting, convulsions, and ultimately death. Despite its toxicity, it has been used historically in medicine, cosmetics, and pigments. 

A small group of elements, called metalloids, have propenies characteristic of both metals and nonmetals. The metalloids boron, silicon, germanium, and arsenic are semiconducting elements (see Section 20.3). 

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