Hydrides, Oxides, Hydroxides, and Halides

Pauling EN Charge density (charge/ionic radius). l.() 0.9 0.8 0.8 0.7 0.7 

Discovered by/date Arfwed.son Davy Davy Bunsen- Bunsen- Percy 

These trends in the oxides and hydroxides are expected on the basis of our fifth and sixth network components, the metal-nonmetal line and the acid-base character of the metal (M) and nonmetal (NM) oxides in aqueous solution. 

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Our network of interconnected ideas helps us to account for many expected properties of the alkali metals. The hydrides, oxides, hydroxides, and halides of these elements are ionic. The oxides and hydroxides are basic in character. Lithium, although stiU an alkali metal with much in common with its congeners, is certainly a good example of the uniqueness principle. It has much in common with magnesium, as forecast by the diagonal effect. 

Following the precedent set in discussing the Group lA elements, we take a close look now at the hydrides, oxides, hydroxides, and halides of this group. 

A survey of the hydrides, oxides, hydroxides, and halides highlights the network components. The hydrides of nitrogen and phosphorus emphasize the uniqueness of the lightest element. Unlike the polar ammonia, the nonpolar phosphine is a poor base and not capable of forming hydrogen bonds. Arsine is less stable than phosphine, and its decomposition is the basis of the criminological Marsh test for the presence of arsenic. 

Note that the reaction products with entries in Table 19.1 are much abbreviated compared with the analogous tables of earlier groups. Only xenon and krypton react with fluorine to produce fluorides. Therefore, instead of following the usual format of describing the hydrides, oxides, hydroxides, and halides of these elements (most of which do not exist), we adopt a historical description of the synthesis of xenon compounds and then briefly expand the discussion to include the small number of examples drawn from krypton and radon chemistry. 

The eight chapters on the representative groups each include sections on (1) the history and discovery of the elements, (2) their fundamental properties as they relate to the growing network of ideas (including an overview of the hydrides, oxides, hydroxides and/or oxoacids, and halides of the group), (3) reactions and compounds... 

As already highlighted in the partial list of Scheme 20, various groups of compounds may act as precursors alkali metals alkali metal hydrides, oxides, hydroxides, alkoxides, halides, carbonates alkali metal salts of organic acids alkyl aluminums alkali aluminum hydrides and their alkoxides quaternary ammonium salts guanidium salts of lactams, etc. 

This early work is summarised in Krause and von Grosse s Organometallische Che-mie which was published first in 1937,11 and which described examples of tetraalkyl-and tetraaryl-stannanes, and of the organotin halides, hydrides, carboxylates, hydroxides, oxides, alkoxides, phenoxides, R2Sn(II) compounds (incorrectly), distannanes (R3SnSnR3), and oligostannanes (RiSn) . 

Between 400 and 430° the hydrogen pressure reaches 1 atm. The melting point (under pressure) is above 800°. Sodium hydride dissolves in fused sodium hydroxide and in fused alkali halides. It is insoluble in liquid ammonia. Water decomposes it immediately and completely to hydroxyl ion and hydrogen. Although sodium hydride is said to be stable in dry oxygen to 230°, traces of elemental sodium present may cause its ignition at lower temperatures. Copper, lead, and iron oxides are reduced by the compound to the free metals. Sulfur dioxide, carbon monoxide, and the halogens are reduced by the hydride to dithionite, formate, and halide ions, respectively. 

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