Alkaline earth group

These elements form two groups, often called the alkali (Group I) and alkaline earth (Group II) metals. Some of the physical properties usually associated with metals—hardness, high m.p. and b.p.—are noticeably lacking in these metals, but they all have a metallic appearance and are good electrical conductors. Table 6.1 gives some of the physical properties. 

Barium is a metallic element, soft, and when pure is silvery white like lead it belongs to the alkaline earth group, resembling calcium chemically. The metal oxidizes very easily and should be kept under petroleum or other suitable oxygen-free liquids to exclude air. It is decomposed by water or alcohol. 

Barium is a member of the aLkaline-earth group of elements in Group 2 (IIA) of the period table. Calcium [7440-70-2], Ca, strontium [7440-24-6], Sr, and barium form a closely aUied series in which the chemical and physical properties of the elements and thek compounds vary systematically with increa sing size, the ionic and electropositive nature being greatest for barium (see Calcium AND CALCIUM ALLOYS Calcium compounds Strontium and STRONTIUM compounds). As size increases, hydration tendencies of the crystalline salts increase solubiUties of sulfates, nitrates, chlorides, etc, decrease (except duorides) solubiUties of haUdes in ethanol decrease thermal stabiUties of carbonates, nitrates, and peroxides increase and the rates of reaction of the metals with hydrogen increase. 

Consequently, they maintain that some displays of the periodic system may, in truth, be superior to others. Whereas the conventionally displayed table, called the medium-long form, has many virtues, it places helium among the noble-gas elements. Some have argued that in spite of appearances, helium should in fact be placed el the head of group 2, the alkaline earth group, which includes beryllium, magnesium and calcium. Helium has two outer-shell electrons as do the elements in the alkaline earth group. 

The use of alkali and alkaline earth group metal ions, especially those of sodium, potassium, magnesium, and calcium, for maintenance of electrolyte balance and for signaling and promotion of enzyme activity and protein function are not discussed in this text. Many of these ions, used for signaling purposes in the exciting area of neuroscience, are of great interest. In ribozymes, RNAs with catalytic activity, solvated magnesium ions stabilize complex secondary and tertiary molecular structure. Telomeres, sequences of DNA at the ends of chromosomes that are implicated in cell death or immortalization, require potassium ions for structural stabilization. 

With Hydrides. —As has already been stated, the hydrides of the metals of the alkali and alkaline earth groups produce hydrogen on being placed in water. However, in only two cases are these reactions worth consideration. 

Strontium has four naturally occurring isotopes (Table 4.2). It is a member of the alkaline earths (Group 2A) along with beryllium, magnesium, calcium, barium, and radium (Fig. 2.4). Strontium substitutes for calcium and is abundant in minerals such as plagioclase, apatite, and calcium carbonate. 

The following Refs give some of the more important studies made with DTA apparatus Refs 1) S. Gordon C. Campbell, "Differential Thermal Analysis of Inorganic Compounds. Nitrates and perchlorates of the Alkali and Alkaline Earth Groups and their Subgroups1, AnalChem 27, 1102-09(1955) (Based on PATR 2079 (Nov 1954) PATR 2200(July 1955)1 2) S. Gordon C. Campbell "Pre-... 

Hardness is the total concentration of alkaline earth (Group 2) ions, which are mainly Ca2+ and Mg2+, in water. Hardness is commonly expressed as the equivalent number of milligrams of CaC03 per liter. Thus, if fCa2+J + [Mg2+] = 1 mM, we would say that the hardness is 100 mg CaC03 per liter because 100 mg CaC03 = 1 mmol CaC03. Water whose hardness is less than 60 mg CaCO, per liter is considered to be soft. If the hardness is above 270 mg/L. the water is considered to be "hard."... 

The selectivities of a Li+ ion-selective electrode are indicated on the following diagram. Which alkali metal (Group 1) ion causes the most interference Which alkaline earth (Group 2) ion causes the most interference How much greater must be [K+] than [Li4"] for the two ions to give equal response ... 

Starting with nitrides of the alkaline and alkaline earth group elements no elemental boron is formed and the c-BN produced is yellow and transparent. Both the quality and the yield of c-BN are increased. 

The diatomic halides and oxides of the alkali and alkaline earth groups must, by definition, have a considerable ionic contribution to their bonding. These diatomics, together with those of Al, Ga and In, are in fact found to lie outside the predicted field for covalent bonds, as shown in Figure 5.6(d). Molecules with dative bonds are expected along the borderline between covalent and ionic types, including several fluorides (of Sb, Si, Sn, Pb, Be and Ag) and chlorides (Si, Sn). They are arbitrarily grouped with the more ionic bonds. 

Sulphites are generally insoluble exceptions are those of the alkali metals, and the hydrogen sulphites of the alkaline earth group. 

All the hydroxides of the Group 1A elements (LiOH, NaOH, KOH, RbOH, and CsOH) are strong bases, but only NaOH and KOH are common laboratory reagents because the lithium, rubidium, and cesium compounds are expensive. The alkaline earth (Group 2A) hydroxides—Ca(OH)2, Ba(OH)2, and Sr(OH)2—are also strong bases. For these compounds 2 moles of hydroxide ion is produced for every 1 mole of metal hydroxide dissolved in aqueous solution. 

Results for the complexes with general formula MAl4n where M is an alkaline-earth (group II) cation... 

The most reactive element in the alkaline earth group is the one with the largest atomic radius and, therefore, the least attraction for its two valence electrons. Knowing this, you can predict that radium, the largest atom in the group, is the most reactive. 

Other zirronimii alloys which have I teen prepared ami studied somewhat- nre those with eohnlt, ulumimimi. magnesium, and silver. Zirconium apparently forms no alloys with Itn, lead, or the mettils of the alkali or alkaline earth groups. 

The alkaline earth group as a whole stands in marked contrast to transition metals and post-transition metals. For example, most of the metals in the periodic table form insoluble precipitates with the sulfide ion (S2), with the result that sulfide ores of transition and post-transition metals are very common in Earths crust. Common examples of metal sulfides include galena (lead sulfide), cinnabar (mercury sulfide), gree-nockite (cadmium sulfide), acanthite (silver sulfide), cobaltite (cobalt arsenic sulfide), sphalerite (ZnS), stibnite (antimony sulfide), several copper sulfides, orpiment and realgar (both forms of arsenic sulfide), and pyrite (iron sulfide). None of the alkaline earths, however, are found as sulfides. 

Alkaline-earth borohydrides, trivalent and tetravalent borohydrides, M(BH4) (M = alkaline-earth. Groups 3 14 in the periodic table, n = valence of M) are synthesized by direct metal hydrides with diborane similar to (15.1) or the metathetical reaction as follows ... 

Application of solid-liquid extraction in the field of Inorganic Chemistry can be illustrated by taking the examples of separation of (i) lithium chloride from the chlorides of other members of the alkali metal group and (ii) calcium nitrate from the nitrates of other members of the alkaline earth group. The solubilities of sodium chloride and potassium chloride are very small in -hexanol and 2-ethylhexanol, whereas the solubility of lithium chloride is large enough so that it can be separated from a mixture of the three chlorides by extraction with these solvents. Similarly, using a 50-50 per cent mixture of absolute ethanol and ether calcium nitrate can be removed from a mixture of the anhydrous nitrates of calcium, barium and strontium. 

The monovalent derivatives of the alkaline earth metals are free radicals that are stable in the thermodynamic sense in the gas phase or when isolated in inert matrices. Molecules such as CaOH have strong bonds (dissociation energy, Dca 0 = 92kcal mol-1) [9,10] but are very reactive species because of the unpaired electron localized on the Ca atom. In spite of the transient nature of these monovalent derivatives, it has proved possible to develop an extensive gas-phase inorganic chemistry for Mg, Ca, Sr, and Ba. No monovalent polyatomic derivatives are known for the Be or the Ra members of the alkaline earth group, except for BeOH. There are two experimental reports on the BeOH [11,12] molecule in... 

The catalyzed oxidation of ethanol to acetic accompanied by acetaldehyde oxidation may be accomplished by use of acetic acid solutions with a cobalt acetate catalyst. In an example, 252 g of acetaldehyde is fed to the catalyst solution for activation, and then 85.4 g of 100 per cent ethanol together with air is introduced. Conversion of ethanol is 94.2 per cent to acetic acid, 3.5 per cent unchanged, and 2.3 per cent to ethyl acetate. Temperatures below 145°C were used. Various other metal acetates have been patented for the above process, including the salts of alkali and alkaline-earth groups, salts of the platinum metals group, and salts of the chromium metals group. A solid palladium-on-alumina catalyst is active in promoting air oxidation of ethanol to acetic acid. ... 

Although metals such as the alkaline earth group should not promote photo-oxidative processes via CTTM transitions, they have been implicated in the photodecomposition of pteridines in seawater (Landymore and Antia, 1978). This has been explained through a structural modification of... 

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