The Group IIA metals

Though diethyl ether is the preferred solvent by a wide margin, other solvents may be more appropriate in these circumstances  

In the first case, the reagent may be prepared in ether in the usual way, the next reactant being added in a higher boiling solvent such as benzene, xylene or di-n-butyl ether. The mixture may then be heated well above 35 , when much ether (but not all of it) distils away. 

The second case requires the complete absence of diethyl ether. The preparation of trimethylarsine (bp 52°), 

One of the best known and most valuable applications of THF has been in the preparation of vinyl and substituted vinyl Grignard reagents, developed to a large extent by H. Normant. 

Organomagnesium halides may also be prepared in hydrocarbons, though careful attention to experimental detail is necessary to obtain good yields. This interesting development is due to D. Bryce-Smith. The hydrocarbon-soluble product from chlorobenzene and magnesium in tetrahydro-naphthalene has the composition (Ph3Mg2Q)x. 

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The binary mixtures lack miscibility in the liquid and solid states with any of the group-IIA metals or with the heavier group-IA metals, K, Rb and Cs (Fig. 1). There is, however, a progressive increase in the miscibility of Li and Na with the group-IIA metal as the atomic number of the latter increases. This is accompanied by compound formation Li with Ca, Sr and Ba, and Na with Sr and Ba " . 

A major problem is the reactivity of the metals, particularly the group-IIA metals, to the atmosphere and the containment vessel. Products containing Ca, Sr and Ba are often as reactive as the metals Be- and Mg-containing products, however, are generally chemically inert. As a result, much of the original work was undertaken on impure samples and products (quoted metal purities of 98% were not uncommon). 

As a result of their reactivity, particular attention must be given to preparation and purification of the metals, the conditions under which the metals, alloys and compounds are handled and the choice of material for the containment vessel. Ultrapure group-IIB metals may be used without further purification, but it is advisable to purify the group-IIA metals by a multidistillation process, the final distillation preferably being carried out in situ. The reactants and products are best handled in an atmosphere of a purified inert gas, usually He or Ar (N2 cannot be used because of the ready formation of group-IIA metal nitrides) alternatively, they can be handled under vacuum or, in rare cases, under halide fluxes. The containment vessel is normally fabricated from a refractory. 

The oxides of the group IIA metals are ionic, so they react with water to produce the hydroxides. 

The sulfides of the group IIA metals generally have the sodium chloride structure, but those of the group IA metals have the antifluorite structure because the ratio of anions to cations is 2. Solutions of the sulfides are basic as a result of the hydrolysis reaction... 

The group IIA metals have the outer electron configuration ns2 with no singly occupied orbital for bonding. The structures are hep for Be and Mg and ccp for Ca and Sr. The structures are bcc for Ba and Ra, for which promotion to (n — l)d1ns1 is more favorable than for the other metals of the family. Metals with filled or nearly filled orbitals (Co, Ni, Pt metals, Cu family, Zn, and Cd) have ccp (3P) or hep (2P) structures. 

As will be discussed in greater detail later, some of the naturally occurring minerals of the Group IIA metals are of great importance. Some of the properties of atoms and ions of the Group IIA elements are shown in Table 7.6. 

At least part of the stabilization of the compounds containing the diatomic anions 022- and 02 comes from the fact that crystal lattices are most stable when the cations and anions have similar sizes (see Chapter 5). The Group IIA metals give normal oxides except for barium and radium, which give peroxides when they react with oxygen ... 

Ternary silicides with the group-IIA metals are known, e.g., the (Ca, Sr)Si2 phases. Although A1 and Si do not form compounds, the addition of other metals can result in industrially important ternary or multicomponent silicidese.g., AlFeSi, AlMnSi, AlCrSi, Ali3Cr4Si4, AljMgjFeSig, AlCuMgSi. 

The group IIA metals are oxidized by halogens and all the alkaline earth dihalides are known h... 

As we might expect, the Group IIA metals also combine with the Group VIIA nonmetals to form binary compounds. Except for BeCl2, BeBr2, and Bel2, these are ionic compounds. In general terms these combination reactions may be represented as ... 

Describe the properties and occurrence of the Group lA metals Describe some important reactions of the Group I A metals Describe some important uses of the Group lA metals and their compounds Describe the properties and occurrence of the Group IIA metals Describe some important reactions of the Group IIA metals Describe some important uses of the Group IIA metals and their compounds Identify the post-transition metals... 

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