LANTHANIDE—TRANSITION METAL ALLOY HYDRIDES

See LANTHANIDE-TRANSITION METAL ALLOY HYDRIDES See Poly(tetralluoroethylene) Metal hydrides... 

Sodium-antimony alloy, 4797 Sodium germanide, 4418 Sodium-zinc alloy, 4798 Titanium-zirconium alloys, 4921 See also LANTHANIDE-TRANSITION METAL ALLOY HYDRIDES... 

See also LANTHANIDE—TRANSITION METAL ALLOY HYDRIDES... 

Magnesium—nickel hydride, 4458 Plutonium(III) hydride, 4504 Poly(germanium dihydride), 4409 Poly(germanium monohydride), 4407 Potassium hydride, 4421 Rubidium hydride, 4444 Sodium hydride, 4438 f Stibine, 4505 Thorium dihydride, 4483 Thorium hydride, 4535 Titanium dihydride, 4484 Titanium—zirconium hydride, 4485 Trigermane, 4415 Uranium(III) hydride, 4506 Uranium(IV) hydride, 4536 Zinc hydride, 4486 Zirconium hydride , 4487 See COMPLEX HYDRIDES, PYROPHORIC MATERIALS See entry LANTHANIDE—TRANSITION METAL ALLOY HYDRIDES... 

Lanthanide iodide silicides, 200 Lanthanide metals, 200 Lanthanide nitrobenzoates, 200 Lanthanide—transition metal alloy hydrides, 201 Lassaigne test, 201 Lead salts of nitro compounds, 201 Lecture demonstrations, 202 Light alloys, 202 Lime fusion, 202 Linseed oil, 202 Liquefied gases, 203 Liquefied natural gas, 203 Liquefied petroleum gases, 203 Liquid air, 204 Liquid nitrogen cooling, 205 Lithium peralkyluranates, 205 Lubricants, 205 Lycopodium powder, 205... 

Several lanthanide-transition metal alloys (LaNi5, PrCo5, SmCo5) readily absorb large volumes of hydrogen under mild conditions, and some of these alloy hydrides function as active hydrogenation catalysts e.g., the title structures, which are pyrophoric in air. Analogous hydrides may be expected to behave similarly. 

Hydrogen reacts at elevated temperatures with many transition metals and their alloys to form hydrides. The electropositive elements are the most reactive, that is, scandium, yttrium, the lanthanides, the actinides and members of the titanium and vanadium groups (Figure 5.20). 

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. 

Hydrogen combines with most of the chemical elements. Here we concentrate on binary hydrides of the typical elements, ignoring those of the transition elements, lanthanides and actinides, which often have metallic properties and so resemble alloys. Binary hydrides are compounds of hydrogen and one other element. A useful classification of the highest hydrides of the typical elements is shown in Figure 5.9. It divides them into three classes salt-like, macromolecular and molecular. 

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