Nitrides elemental halogens

Nitrogen and sodium do not react at any temperature under ordinary circumstances, but are reported to form the nitride or azide under the influence of an electric discharge (14,35). Sodium siHcide, NaSi, has been synthesized from the elements (36,37). When heated together, sodium and phosphoms form sodium phosphide, but in the presence of air with ignition sodium phosphate is formed. Sulfur, selenium, and tellurium form the sulfide, selenide, and teUuride, respectively. In vapor phase, sodium forms haHdes with all halogens (14). At room temperature, chlorine and bromine react rapidly with thin films of sodium (38), whereas fluorine and sodium ignite. Molten sodium ignites in chlorine and bums to sodium chloride (see Sodium COMPOUNDS, SODIUM HALIDES). 

The metal reacts with halogens above 200°C forming its trihalides. It combines with nitrogen above 1,000°C producing a nitride, YN. It combines at elevated temperatures forming binary compounds with most nonmetals and some metalloid elements such as hydrogen, sulfur, carbon, phosphorus, silicon, and selenium. 

The relation between heat of formation and stability is not a simple one. A compound will be unstable at low temperatures if its heat of formation is negative if the compound is formed from one element that is solid at room temperature and a second element that is gaseous, the pressure of the latter will be higher than one atmosphere if the heat of formation per mol gas formed is lower than TAS, or 300 X 35 cal = 10 kcal. A halide, therefore, will be unstable at room temperature for it will decompose into its compounds when V (heat of formation per equivalent) is smaller than X 10 kcal, because two equivalents must decompose to form one mol of halogen (for an oxide this limit is J X 10 kcal and for a nitride i X 10 kcal). Thus, in spite of a heat of formation as low as 2 kcal per equivalent, a nitride will be perfectly stable at room temperature. 

In Chapters 20 and 21 we shall look at individual elements of the c -block in detail. However, a few general points are given here as an overview. In general, the metals are moderately reactive and combine to give binary compounds when heated with dioxygen, sulfur or the halogens (e.g. reactions 19.1-19.3), product stoichiometry depending, in part, on the available oxidation states (see below). Combination with H2, B, C or N2 may lead to interstitial hydrides Section 9.7), borides Section 12.10), carbides Section 13.7) or nitrides Section 14.6). 

Iron is reactive and, if sufficiently finely divided, is pyrophoric in air. It forms binary compounds by direct reaction with many elements, and some of these are described in more detail later. It reacts with oxygen, sulfur, halogens, phosphorus, and even forms a nitride with dinitrogen. With... 

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