435

CHAPTER XXII.

THE ELEMENTS OF GROUP I.

12

Even series. Li=7-01

load

2
4
6
8

10
K=39-04 Rb=85-2 Cs=132-7
Group I.

1
3
5
7

11 lodd series. H=1 Na=23 Cu=63-2 Ag=10766

Au=197 Even-series elements, and second mem- LITHIUM.

SODIUM.
POTASSIUM. RUBIDIUM.

CAESIUN. ber of odd.

series Atomic weights

7-01
23
39-04
85.2

132-7
The molecular weights of sodium and potassium are the same as their atomic
weights; the other elements of the family have not yet been gasified, and therefore

their molecular weights are unknown. Sp. grs. (approx.)

:59

.98
.87
1.52

1.88 Melting points 180°

950-5
58°-62

389

26° -27° (approx.) Atom. weights

2

These metals all combine directly and rapidly with the halogens, and with sulphur. The following compounds of these metals have been gasified and their molecular weights determined, KI, RbI, RbCI, RbI, CsCl, CsI; in these molecules the atoms of potassium, rubidium, and caesium are monovalent.

The five elements we are now considering form the family 436 of alkali metals ; the prominent chemical characteristics of these metals have been already examined in Chap. XI. pars. 163–168. It will suffice to summarise these characteristics here.

Oxides and hydroxides, MO and MOH, are strongly basic and alkaline; very soluble in water, M,0 forming MOHAq. The hydroxides are formed at ordinary temperatures by direct interaction of oxides M,0 with water; they are not decomposed by heat alone. Oxides of rubidium and caesium have not yet been isolated. The oxides Na,o,, K,,, and a few others, are known.

Sulphides and hydrosulphides, M S and MSH, are strongly basic; they interact with many more negative sulphides to form thio-salts. No sulphide of rubidium or caesium has yet been isolated. MS, M,Sz, M S., M.Ss, are known, where M= Na or K.

Haloid compounds, MX, are very stable solids, soluble in, and not decomposed by, water. The chlorides, except LiCl, form many double compounds with chlorides of less positive elements, e.g.

PtCl . 2MCI; SbC1.6MCI. Salts, M.X where X = SO, 2NO,, CO3, 2010, PO, &c. are very definite, stable, bodies; very few basic salts exist. Many of the salts combine with similar salts of less positive elements forming double salts; the alums M SO..X,380, 24H,0 are important (X = Al, Cr, Fe, Ga, In). "Lithium does not form an alum. Most of the salts are easily soluble in water.

Lithium is less like the other members of the family than they are like each other. LiOH is much less soluble in water than the other hydroxides ; Li,CO, and Li PO, are also much less soluble than the other carbonates and phosphates; Li, SO. does not combine with Al.350, a double salt 3Li so,.Cr,($0.) is known, but it is not an alum. All the elements of the family except lithium form sulphates of the form MHSO, ; Li, H (SO) is known.

The odd-series elements of Group I. shew great differences 437

2

4

5'

3

3'

4

4

in their physical and chemical properties; sodium is evidently closely allied to the even-series members; hydrogen must be considered apart from the other elements ; copper, silver, and gold exhibit resemblances but also marked differences.

Odd-series ele-
COPPER.
SILVER.

GOLD.
ments
(hydrogen and so-

dium omitted)
Atomic weights

63.2
107.66

197
The molecular weights of these elements are unknown.
Sp. grs. (approx.)

8.8
10-5

19.5
Melting points
1050°
1000°

1200°
(approx.)
Sp. heats
.095
057

*0324
Atomic weights

7.2
10:3

10:1
spec. graus.
Appearance and Heavy, lustrous, red- White, very lustrous, Yellow-red, lustrous,
general physical dish, solid; very tena- hard, solid; very mal- rather soft, solid; ex-
properties. cious and ductile; mal- leable, tenacious, and tremely nialleable and

leable; very good con- ductile; good conductor ductile; very tenacious;
ductor of' heat and of heat and electricity good conductor of heat
electricity.

Crystallises in regular and electricity.
Crystallises in regular octahedra.

octahedra.
Occurrence and Metal occurs native; Metal occurs native; Metal occurs native;
preparation. also as sulphide &c., also as sulphide fre- generally alloyed with

frequently with similar quently with Cugs, silver, and frequently
compounds of silver, Sb2S3, &c.; Agil' also also with small quanti-
iron, &c. Fairly widely occurs. Most lead ores ties of copper and iron.
distributed and in con- contain small quanti- Compounds of gold do
siderable quantities.
ties of silver.

not occur.
Prepared by roasting Widely distributed, Widely distributed,
Cuns in air till mixture generally in compara- generally in small
of CuO and Cu2S is pro- tively small quantities. quantities.
duced, then shūtting off Prepared by heating Preparing by washing
air and raising tempera- Ag25 with salt in air away gangue &c., some-
ture, when Cu2S+2CuO (Ag2S + 2NaCl +40 times by mixing crushed
=4Cu + SO2

= Na2S04+2 AgCl), auriferous quartz and then agitating with with mercury whereby iron (2AgCl + Fe a gold-amalgam is =FeCl2+2Ag).

formed, and then re

moving Hg hy heating. General chemical Oxidised to CuO by Slowly oxidised by di- Not oxidised by direct properties. strongly heating in air. rect union with oxygen union with oxygen.

Combines directly with at very high tempera- Combines directly with
the halogens and with tures. Molten silver the halogens at mode-
sulphur, at moderately absorbs oxygen but the rately high tempera-
high temperatures. gas is evolved again as tures, but not with
Interacts with many the metal cools. sulphur.
acids to forni salts. Combines directly at Does not interact di-
Decomposes steam moderate temperatures rectly with many acids,
slowly at full red-heat with the halogens and insoluble in most acids;
giving CuO and H. with sulphur.

but a few salts are ob-
Interacts with many tained from the oxide.
acids to form salts. No reaction with steam.
Does not react with
steam.

438

General formulae and chemical characters of compounds. The only compounds which have been gasified and the vapourdensities of which have been determined are Cu,cl, and AgCl. The following formulae are not necessarily molecular.

2

4

3

6

2

-2?

3

2

2

3

4

Copper forms two series of compounds, represented by the following; (1) Cu,0, Cu,Ci,, Cu S02; (2) Cuo, Cuci,, Cuso..

Silver forms one series of compounds represented by Ag, 0, Ag, Cl,, Ag, SOM

“Gold forms two series, represented by, (1) Au,0, Au,Cl,, (2) Au,o,, Au,cl, or Auci,.

A hydride of copper, Cu, H,, is known.

Oxides. M,O where M = Cu, Ag, Au; MO where M = Cu,
Ag, Au; M,0, where M = Au only.

Sulphides. M.S where M = Cu or Ag; MS where
M = Cu; M,Swhere M = Au.
Haloid compounds. M,cl, where M = Cu, Ag, Au;

Cl
MCl, where M = Cu; MCl, where M = Au.

Salts. Most of the copper salts belong to the form CuX where X =S0, 2NO, CO, {PO, 2010,, &c.; a few are known of the form Cu x. The definite silver salts all belong to the form Ag, X.

ve

ery few salts of gold are known; some seem to be similar in composition to the silver salts and to be represented by the formula Au,X, others belong to the form Au,3x.

The compositions of the compounds of copper silver and gold may be represented by the following general formulae; X=0, S, Cl, Br,, I., SO, 2003, 2NO,, {PO, &c.

M,X.
Cu,0, Cu,S, Cu,Ci,, Cu,12, and a few unstable salts e.g. Cu,80z.
Ag,0, Ag,Cla, Ag, In, Ag, Br, &c., and all salts e.g. Ag ŠOs.
Au,0, Au,C1,, Au, In, and a very few unstable salts e.g. Au,S,Oz.

MX.
Cuo, CuCl2, &c., and many well-marked salts.
Ag0, no salts.
Auo, AuSO4

M,Xg.
Au,O3, Au,Cla, Au,(OH)8, and a few salts e.g. Au(NO3)3. HNO3.3H,0.
No Cu or Āg compounds.
The oxides M,0 are prepared; in the case of Ag,0 by 439

1 adding potash or soda to a solution of a salt of silver (e.g. 2 AgNO Aq + 2KOHAq = Ag,0 + 2KNO,Aq+H,0); in the cases of Cu O and Au,O by reducing solutions of copper or gold salts in the presence of an alkali, CuSO, Aq may be reduced by grape sugar, and AuCl Aq by sulphur dioxide.

Cuprous oxide Cuois fairly stable, but it is easily oxidised to CuO by heating in air; with acids it forms cupric salts, e.g. Cuso,; the cuprous salts, which correspond to Cu,0,

3

2

=

2

3

3

are not obtained from the oxide. Argentous oxide, Ag, 0, is a stable compound which interacts with acids to form salts and water; e.g. Ag,0 + 2HNO,Aq = 2AGNO,Aq +H,0; it is decomposed at about 250° to silver and oxygen.

This oxide is strongly basic, in some of its reactions it closely resembles the oxides of the alkali metals; an hydroxide of silver has not however been isolated. Aurous oxide, Au,0, is very easily decomposed; it rapidly absorbs oxygen with formation of auric oxide Au,0,: one or two salts corresponding to Au, are known, but they are not obtained from the oxide; the oxide is said to be soluble in cold water.

The oxides MO are prepared; CuO by adding an alkali to the

solution of a cupric salt, and heating the hydrated oxide CuO.HO which is precipitated (e.g. CuSO, Aq + 2KOHAq = CuO.HO+K SO, Aq; and CuO.H,0 heated, even in contact with water,=ČuO+H,O); Ago by passing ozonised oxygen over finely divided silver; Aug by heating hydrated auric oxide, Au,0,.H,O, to 160°

Cupric oxide CuO is basic, it interacts with acids to form a large series of salts CuX(X = SO, &c.); this oxide is not decomposed by heat alone; most reducing agents remove the oxygen from heated CuO. The oxide does not combine directly with water, but the hydrate CuO.H,O is obtained, indirectly, as described above. Argentic oxide, or silver peroxide, Ago (or Ag, 0,) is easily decomposed; heated to 110° it suddenly evolves oxygen and silver remains; this oxide interacts with acids to form argentous salts (e.g.. Ag,SO,, Ag2NO3, &c.) and oxygen, that is, it behaves as a peroxide.

Auro-auric oxide Auo (Au,0, is usually known as auric oxide) is easily decomposed ; at 173° it is separated into gold and oxygen; it does not appear to form any salts by reacting with acids.

Auric oxide, Au,0, the only representative of the M.O, class of oxides, is prepared by adding an alkali to a solution of auric chloride Aucl, (magnesia seems to be the best alkali to use), drying the precipitated Au, Og.H,0, and then carefully heating it to 100°. The oxide is easily decomposed by heat, or by exposure to light; it dissolves in nitric acid, and the salt Au(NO3)2.HNO.3H0 can be obtained from this solution; it interacts with hydrochloric acid to form the compound AuCl,.HCl, and with hydrobromic acid to form AuBrz. HBr; these compounds are monobasic acids forming salts such as KAuCl, and KAuBrı. Hydrated auric oxide, Au,Og. H,O,

+

3

3

3