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SGCh21 - Chapter Twenty-One NONMETALLIC ELEMENTS AND THEIR...

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416 Chapter Twenty-One NONMETALLIC ELEMENTS AND THEIR COMPOUNDS Hydrogen Carbon Nitrogen and Phosphorus Oxygen and Sulfur The Halogens HYDROGEN STUDY OBJECTIVES 1. Write chemical equations to show the reactions used to prepare hydrogen. 2. Describe the chemical properties and major uses of hydrogen. General Properties of Nonmetals. The nonmetal elements with the exception of hydrogen are located in the upper right hand corner of the periodic table. The properties of nonmetals are more varied than those of metals. Several nonmetal elements are gases, and nonmetals exhibit both positive and negative oxidation numbers. In this chapter we will discuss the chemistry of a number of important nonmetallic elements: hydrogen, carbon, nitrogen, phosphorus, oxygen, sulfur, fluorine, chlorine, bromine, and iodine. Hydrogen . Hydrogen is the most abundant element in the universe and the tenth most abundant element in the Earth's crust where it is found in combination with other elements. At ordinary temperatures elemental hydrogen is a diatomic molecule. Commercially, the most important large-scale preparation is the reaction between propane and steam in the presence of a catalyst at 900°C: C 3 H 8 (g) + 3H 2 O(g) 3CO(g) + 7H 2 (g) In another process steam is passed over a bed of red-hot coke (the water gas reaction): 1000°C C(s) + H 2 O(g) CO(g) + H 2 (g) Small quantities of hydrogen are prepared in the laboratory by the reaction of zinc with hydrochloric acid. Zn(s) + 2HCl(aq) ZnCl 2 (aq) + H 2 (g) Properties of Hydrogen. Hydrogen can be oxidized to the H + ion and can be reduced to the H ion (hydride ion) as well. Thus, it resembles the alkali metals and the halogens, respectively. It also forms diatomic molecules as do the halogens elements. Like the alkali metals, hydrogen forms ions with a +1 charge. As a result of these properties, there is no totally satisfactory position for hydrogen in the periodic table. Hydrogen forms binary compounds called hydrides with a large number of elements; it reacts directly with most active metals to form ionic hydrides .
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Nonmetallic Elements and Their Compounds / 417 2Na(s) + H 2 (g) 2NaH(s) 2Al(s) + 3H 2 (g) 2AlH 3 (s) The ionic character of these metal hydrides increases as we move down a group of the periodic table. Metal hydrides react with water to form hydrogen gas and the metal hydroxide. NaH(s) + H 2 O(l) NaOH(aq) + H 2 (g) Uses of Hydrogen. Hydrogen is used in the synthesis of ammonia, an important fertilizer. The Haber process for synthesizing ammonia was discussed in Chapter 14. Ammonia which results from the reaction of hydrogen with nitrogen is an example of a covalent hydride . N 2 (g) + 3H 2 (g) 2NH 3 (g) Hydrogen is used in the production of margarine and cooking oil to convert polyunsaturated fats which contain C C double bonds into partially hydrogenated products.
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