Group IIA hydrides

Lithium, alone of the Group IA hydrides, has a heat of formation comparable with those of the Group IIA compounds. 

Molten hydrides of Groups IA and IIA are good electrical conductors, and hydrogen is liberated at the anode as a result of the oxidation of IF ... 

Most of the Group IA and IIA metals react with hydrogen to form metal hydrides. For all of the metals in these two groups except Be and Mg, the hydrides are considered to be ionic or salt-like hydrides containing H ions (see Chapter 6). The hydrides of beryllium and magnesium have considerable covalent character. The molten ionic compounds conduct electricity, as do molten mixtures of the hydrides in alkali halides, and during electrolysis of the hydrides, hydrogen is liberated at the anode as a result of the oxidation of H ... 

Formation of Bonds between Hydrogen and Group iA or IIA Metals 153 1.8.2. Alkali-Metal Hydrides... 

Hydrides are broadly of three types, saline, covalent and metallic. Saline hydrides are formed by the alkali metals (Gp. lA), the alkaline earths (Gp. IIA) and the lanthanides they have ionic lattices, high melting points and, when fused, are electrolytes. Elements of the B Groups from IIIB to VIIB have covalent hydrides, most of them gaseous at room temperature. The metallic hydrides characteristic of some of the transition elements are in effect alloys and usually lack the stoichiometric composition of normal chemical compounds. 

The term hydro has been used throughout in this article in preference to the more commonly used terms hydride or hydrido. These latter terms imply that the hydrogen atom bonded to a transition metal has a high electron density comparable to the saline hydrides of Groups lA and IIA. A number of hydro-transition metal compounds do, indeed, show chemical behavior characteristic of a hydridic hydrogen. However, this is in no way general, and, since it is a particularly poor assumption for the compounds of platinum, the use of the term hydro should avoid any misconception on the part of the reader not familiar with this area of chemistry. 

The hydrides of groups lA and IIA, nd IIB show little tendency to add to olefins unless there is some kind of special stabilizing effect, such as conjugation in the product. These reactions are highly ionic and are favored by solvents and ligands which increase the ionic character of the hydride. Severe conditions of temperature and pressure are needed, and yields of alkyl products are poor. Most of the simple alkyls of groups lA and IIA lose olefin on heating to form a metal hydride. The rate of olefin elimination follows the sequence primary < secondary < tertiary. 

The highly reducing hydrides of groups lA and IIA have not been examined for reduction of CO2 and CS2 in any systematic way. Their insolubility in uncomplexed form and capacity to over reduce do not make them attractive reagents. Na[HB(OCH3)3] reacts exothermically with CO2 to give sodium formate and methyl borate (AlHa) reacts readily with CO2 hydrolysis of the product gives an optimized maximum yield of formic acid of 52%. ... 

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