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Chapt21

Accounting

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Back Forward Main Menu TOC Study Guide TOC Textbook Website MHHE Website
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C H A P T E R 21 Nonmetallic Elements and Their Compounds I N T R O D U C T I O N O F THE 112 KNOWN ELEMENTS , ONLY TWENTY - FIVE ARE NONMETALLIC . U NLIKE THE METALS , THE CHEMISTRY OF THESE ELEMENTS IS DIVERSE . D ESPITE THEIR RELATIVELY SMALL NUMBER , MOST OF THE ESSENTIAL EL - EMENTS IN BIOLOGICAL SYSTEMS ARE NONMETALS ( O, C, H, N, P, AND S ). T HIS GROUP ALSO INCLUDES THE MOST UNREACTIVE ELEMENTS THE NOBLE GASES . T HE UNIQUE PROPERTIES OF HYDROGEN SET IT APART FROM THE REST OF THE ELEMENTS IN THE PERIODIC TABLE . A WHOLE BRANCH OF CHEMISTRY ORGANIC CHEMISTRY IS BASED ON CARBON COMPOUNDS . I N THIS CHAPTER WE CONTINUE OUR SURVEY OF THE ELEMENTS WITH A DISCUSSION OF NONMETALS . T HE EMPHASIS WILL BE ON IM - PORTANT CHEMICAL PROPERTIES AND ON THE ROLES OF NONMETALS AND THEIR COMPOUNDS IN INDUSTRIAL , CHEMICAL , AND BIOLOGICAL PROCESSES . 21.1 GENERAL PROPERTIES OF NONMETALS 21.2 HYDROGEN 21.3 CARBON 21.4 NITROGEN AND PHOSPHORUS 21.5 OXYGEN AND SULFUR 21.6 THE HALOGENS 831 Back Forward Main Menu TOC Study Guide TOC Textbook Website MHHE Website
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Recall that there is no totally suit- able 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 nonmetals are solids at room temperature. Unlike metals, nonmetallic elements are poor conductors of heat and electricity; they exhibit both positive and negative oxidation numbers. A small group of elements, called metalloids, have properties characteristic of both metals and nonmetals. The metalloids boron, silicon, germanium, and arsenic are semi- conducting elements (see Section 20.3). Nonmetals are more electronegative than metals. The electronegativity of elements increases from left to right across any period and from bottom to top in any group in the periodic table (see Figure 9.5). With the exception of hydrogen, the nonmetals are concentrated in the upper right-hand corner of the periodic table (Figure 21.1). Compounds formed by a combination of metals and nonmetals tend to be ionic, hav- ing a metallic cation and a nonmetallic anion. In this chapter we will discuss the chemistry of a number of common and im- portant nonmetallic elements: hydrogen; carbon (Group 4A); nitrogen and phosphorus (Group 5A); oxygen and sulfur (Group 6A); and fluorine, chlorine, bromine, and io- dine (Group 7A). Hydrogen is the simplest element known—its most common atomic form contains only one proton and one electron. The atomic form of hydrogen exists only at very high temperatures, however. Normally, elemental hydrogen is a diatomic molecule, the product of an exothermic reaction between H atoms: H( g ) H( g ) 88n H 2 ( g ) H ° 436.4 kJ 832 NONMETALLIC ELEMENTS AND THEIR COMPOUNDS 21.1 GENERAL PROPERTIES OF NONMETALS 21.2 HYDROGEN 1 1A 2 2A 3 3B 4 4B 5 5B 6 6B 8 10 7 7B 9 8B 11 1B 12 2B 13 3A 14 4A 15 5A 16 6A 17 7A 18 8A 1 H 3 Li 11 Na 19 K 37 Rb 55 Cs 87 Fr 20 Ca 38 Sr 56 Ba
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