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CHAPTER XIX.

12

THE ELEMENTS OF GROUP II.

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Even series. Be= 9.08 Ca=39.9 Sr= 873 Ba=136-8
Group II.

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Odd series. Mg=24 Zn=649 cd=112

Hg = 199•8
Even-series BERYLLIUM.

CALCIUM.
STRONTIUM,

BARIUM. elements Atomic weights

9.08
39.9
873

136-8
The molecular weights of these elements are unknown.
Sp. grs. (approx.)

1.7
1.58
2-5

3.75
Sp. heats
6 (at abt. 5000)

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not determined. not determined. increases rapidly as

temp. increases. Melting points not determined. full red-heat; above Ba; moderate below red-heat. (approx.)

above Sr.

red-heat. Alom. weights

54
253
34.9

36.5 spec. gravs. Colour, appear- White, lustrous, Whitish-yellow;abt. Clear whitish-yel. Gold-yellow; fairly ance, fc. hard.

as hard as lead, very low; harder than ductile.
ductile, but becomes lead, ductile and
brittle when ham- malleable.

mered. Occurrence and Not widely distri- Carbonate, phos- Carbonate and sul- Carbonate,sulphate, preparation buted. Oxide occurs phate, sulphate, sili- phate occur in some and silicate, occur

in a few rocks. cate, &c. very widely rocks and water, but in some rocks, water, Prepared by reduc- diffused in rocks, not very widely and plants, but not ing fused BeCl, by water, plants, and diffused. Prepared very widely diffused. Na, not by electro- animals. Prepared by electrolysis of Prepared by eleclysis of BeCl2 by electrolysis of fused SrCl2, or by trolysis of BaCl2

mixture of CaCl2 reducing SrCl, by mixed with NH CI, with SrCl2 and Zn - Na amalgam. or by reducing NH4C1, or by re

BaCl2 by vapour ducing CaCl2 by

of K. Zn - Na amalgam. General chemical Not oxidised in ord. Quickly oxidises in Closely resembles Closely resembles properties air; even when heat- moist air; decom- Ca; decomposes cold Ca.

ed in 0 is only super- poses cold H20 ra- H20 more rapidly. Oxide (BaO) very
ficially oxidised. pidly; burns in air Oxide (Sr0) strongly strongly basic and
Does not decompose at red heat.

basic and alkaline. alkaline.
H20 even at red Combines with CI,
heat.

Br, I, P, and S, at
Combines with CI, high temperatures.
Br, and I, at high Oxide (Cao)strongly
temps.; does not basic and alkaline.
combine directly Strongly positive
with S.

metal.
Dissolves in
KOHAq forming
Beo and H.
Oxide (BeO) basic
but not alkaline.
Distinctly metallic.

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General formulae and chemical characters of compounds. (M = Be, Ca, Sr, or Ba). MO, MO,H,,MO, (no Beo, known), MS, MS, H, (no Bes H, known), řX, (X=F, CI, Br, I), MSO,, M2NO, MCO2, &c. The only compounds which have been gasified are Beci, and BeBr..

The oxides MO may be prepared by direct combination of metal with oxygen, or by decomposing the hydroxides (MO,H) by heat (Bao H, is not decomposed by heat alone). The hydroxides MÓ,É, where M=Ca, sr, or Ba, are obtained by combining water with the oxides MO, or by precipitating solutions of salts of M by potash or soda. Beryllium hydroxide, Beo H,, is prepared by precipitating an aqueous solution of a salt of Be by NH, Aq, and drying at about 100°. The peroxides MO, (M = Ča, Sr, or Ba) are

. produced by interactions between HO, Aq and solutions of salts of M; the compounds MO,. «HO thus obtained lose water when dried, when M = Ba the drying is conducted over sulphuric acid in vacuo, when M=Sr the hydrated peroxide is dried at 100°, and when M=Ca the temperature is raised to 130°. Bal, is also obtained by heating BaO in oxygen at about 200°; the other oxides MÒ do not directly combine with oxygen.

The oxides CaO, Sro, and BaO are somewhat soluble in water; the solubility increases from Cao to BaO. The solutions are alkaline towards litmus paper; they interact with acids to produce salts and water; they precipitate hydrates of iron, copper, manganese, and many other heavy metals, from solutions of salts of these metals; they absorb and combine with carbon dioxide. These oxides combine with water forming hydroxides which are very stable compounds. Beryllium oxide, Beo, is insoluble in water; it does not directly combine with water. This oxide has no alkaline properties; it interacts with acids to form salts and water. None of these oxides, except Beo, is easily reduced, e.g. by heating with C, or in H or CO.

The hydroxides MO H,, where M= Ca, Sr, or Ba, are fairly soluble in water; the solubility increases as the atomic weight of M increases; Cao H, is decomposed by heat (to Cað+H,O) at 300°—400°; Sro,H, at a higher temperature ; BaO,H, is not decomposed even at a full red heat. These hydroxides do not interact with solutions of the alkalis (potash, soda, ammonia). They form compounds with water (hydrates); the most marked of these hydrates have the composition

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MO H..8H.O. Beryllium hydroxide, BeO, H, is easily
changed by heat to Beo+H,0; it is insoluble in water and
has not an alkaline reaction towards litmus. When freshly
precipitated this hydroxide dissolves in KOHAq or NaOHAq,
but is reprecipitated on heating. The freshly precipitated
hydroxide also dissolves in (NH),CO, Aq and K CO Aq; by
boiling the solution in (NH),CO, Aq a basic carbonate of
beryllium is precipitated. Beo, , forms a number of

.
,

a
hydrates the compositions of which vary with small variations.
in the conditions under which they are prepared; they are all
readily decomposed by heat.

The peroxides MO, (M=Ca, Sr, Ba) shew no alkaline reaction towards litmus ; they are insoluble in water, but all form compounds (hydrates) with water. They are all decomposed by heat to MO+0; Bal, is the most stable towards heat. No peroxide of beryllium has been obtained.

The oxides and hydroxides are all white solids; Beo H, is much more gelatinous than the other' hydroxides.

The specific gravities of the oxides MO are, approximately, 3.08 for Beo, 3.15 for CaO, 4.5 for Sro, and 5.4 for BaO; of the hydroxides MO, H, 2.08 for Cao H, 3.62 for Sro H, and 4:49 for BaO H. The heats of formation of these oxides and hydroxides, in aqueous solutions, from calcium to barium, increase as the atomic weights of the metals increase.

The sulphides Cas, Srs, and BaS are prepared (1) by 399 heating the oxides MO in a stream of carbon disulphide mixed with carbon dioxide, (2) by heating a mixture of the sulphates MSO, with charcoal ; MSO, +4C = MS + 4CO.

The hydrosulphides MS H, are usually obtained by reactions between the hydroxides, generally in aqueous solution, and sulphuretted hydrogen ; thus

MO,H, + 2H S = MS, H, + 2H,0, These compounds are also formed when the sulphides MS interact with a little water;

2MS + 2H,0 = MS,H, + MO,H. The sulphides and hydrosulphides are white, or yellowish white, solids; they are more easily decomposed by heat, and by interaction with water, than the corresponding oxygen compounds. Besides the compounds MS and MSH the following sulphides are known : Cas, Cas, Srs, Bas, BaS.HO.

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Beryllium does not combine directly with sulphur, nor is a sulphide produced by heating Beo in carbon disulphide vapour, or by heating BeSo, in hydrogen or sulphuretted

hydrogen. 400 The haloid compounds MX-where X = F, Cl, Br,

or I, and M = Ca, Sr, or Ba-are obtained by interactions between the oxides, hydroxides, or carbonates, of the metals and aqueous solutions of the haloid acids HX. The cor. responding beryllium compounds, Beci,, BeBry, and Bely, are prepared by strongly heating an intimate mixture of beryllium oxide and finely divided carbon in chlorine, bromine, or iodine vapour, respectively; BeQ+C+X, =Bex, + CO. Solutions of beryllium oxide, or carbonate, in haloid acids yield oxyhaloid compounds on evaporation, e.g. BeO.Beci,

The compounds MX, where M is Ca or Sr usually crystallise with 6H,O, ie. the crystals have the composition MX, 64,0; when M = Ba the compounds MX, usually crystallise with 21.0. The crystallised fluorides however of all the metals Ca to Ba seem to be anhydrous. Hydrates of BeX, crystallise from solutions of the three compounds in the haloid acids HX. The compounds MX, are white solids, which melt at high temperatures; e.g. M.P. of CaCl,=719°, CaBr =676o, Cal,=631"; M.P. of Srcl, = 825°, SrBr = 630°, Srl, = 507°; M.P. of BeCI, = abt. 600°. BeBr, and Beči, have been gasified without decomposition. The haloid compounds of Ča, Sr, and Ba, with the exception of the fluorides, are very soluble in water, and are also soluble in alcohol; the Be coinpounds are not soluble in water. The Be compounds easily form oxy haloid compounds of more or less complex composition expressible by the general formula «BeX .yBeO; the haloid compounds of Ca, Sr, Ba, form only a few similar compounds, which are obtained by boiling solutions of MX, with the oxides MO. Most of the haloid compounds of Ca, Sr, and Ba, absorb and combine with ammonia, generally producing compounds of the form MX,.6NH,; these are easily decomposed by heat. These haloid compounds, except the fluorides, do not shew any great tendency to combine with other haloid compounds

and so produce double salts. 401 The salts of the metals Be, Ca, Sr, Ba, i.e. the compounds

obtained by replacing the hydrogen of acids by these metals, are very numerous, The salts of Ca, Sr, and Ba, as a class are very definite and stable compounds; the oxides and hydroxides of these metals interact with most acids in aqueous

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solutions to form normal salts. With the weak acids, especially with boric acid, these metals also form basic salts : e.g. 3Ca0.5B 0,, and 38r0.B, A few double salts are known of these three metals;

e.g. Casở,.K SO, H,0; and SrSO,.K,80 The greater number of these double salts are derivatives of the weaker acids ; e.g. Ba (NH.) AsO,, and 2CaO.B.Oz. Na B,0,.

,0.15H.0.

0 The salts of beryllium are less definite compounds than those of the other three metals we are considering : many are basic salts, e.g.

3BeO.CO,; 3BeO.S03; 2Be0.SOz; 7Be0.35e0.14H,O. The normal Be salts are more easily decomposed by heat, or by heating in presence of water, than the salts of Ca, Sr, and Ba. Beryllium also forms many double salts, e.g. Be (NH)PO,; BeSO,.K.SO,.2H2; 3BeCO,.2(NH) CO, ;

3BeSiOz. Al,(SiO2)3 The carbonates MCO, are all decomposed by heat alone to MO+CO,; their stabilities towards heat increase as the atomic weight of M increases.

The existence of the gaseous molecules BeCl, and BeBr, indicates that the atom of beryllium is divalent; as the vapour densities of no compounds of the metals Ca, Sr, Ba, have as yet been determined, we cannot be certain as to the valency of the atoms of these elements, but judging from the analogies between these three, and the other, members of Group II., it is probable that the atoms of these elements are divalent.

The three elements, calcium, strontium, and barium, are evidently very closely related; they are much more like each other than any of them is like beryllium.

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