2

4

chlorides directly from the acids HMO, and H.MO1; by the slightly acidic functions of the hydrides MH..

Tellurium does not exist in more than one form; the acids H.TeO, and H.TeO, are not produced by the direct interactions of the oxides TeO, and TeO, with water; the hydride TeH, shews no acidic properties; the anhydride TeO, combines with some acids (e.g. TeO,.2HCl is known); some of the physical properties of tellurium approximate to those of the metals.

139

The existence of the stable gasifiable tetrachloride TeCl; the formation not only of ditellurates MTe,O,, but also of tetratellurates MTe O, and of salts of the form MTe,O, (M = K,, Ba, &c.); the unreadiness to enter into chemical reaction with alkalis or alkaline carbonates of the oxide TeO, ; these are some of the properties in which tellurium approaches the higher members (W and U) of the even series of Group VI.

2

OXYGEN is the first member of the even-series of the group now under consideration. Oxygen is a typical non-metallic or negative element both in its chemical and physical properties (s. Chap. VIII.). Nevertheless the properties of some of the compounds of this element suggest the properties of the other elements of the group in which oxygen occurs. Thus oxygen forms two compounds with hydrogen, water H2O and hydrogen peroxide H2O,, but neither is acidic; oxygen combines with the positive elements to form oxides the composition of which is frequently similar to that of the sulphides and selenides of the same elements, compare for instance the formulae MO and MS where M = Cu, Fe, Mg, Ni, Co, Mn, Ca, Ba, Sr, K., Na, &c.; most of the oxides of positive elements are basic, some however as we have seen are acidic; most of the sulphides of positive elements interact with acids to form salts and hydrogen sulphide, some however interact with alkaline sulphides to form thio-salts.

2

The compounds of oxygen with chlorine CIO, and (?) Cl ̧O, do not resemble the chlorides of the other members of Group VI. in composition, but the oxide OCl, is analogous in composition to MC1, when MS, Se, Te, Cr, Mo, or W. The compounds of oxygen with chlorine are very easily decomposed by heat and reagents generally; in this they resemble the compounds of sulphur and selenion with chlorine. The existence of the gaseous molecules O, and O,, Se, and Se S, and S., emphasises the resemblance between oxygen, sulphur,

2

2

421

422

5 2

and selenion. Oxygen forms a solid, stable, compound with iodine, O,I,; although the composition of this compound is not similar to that of the iodides of the other elements of Group VI., the fact of the existence of this stable compound suggests the existence of the stable iodides of tellurium, chromium, and tungsten. The existence of many definite and stable compounds of oxygen with non-metallic elements (oxides of As, B, C, I, N, P, Si) shews that oxygen is to some extent positive in its chemical properties: the compositions of these oxides are very frequently similar to those of the sulphides of the same elements when sulphides of these elements exist.

Group VI., then, is evidently divided into two well marked sub-groups or families; one of these families consists of the elements chromium, molybdenum, tungsten, and uranium; the other is formed of sulphur, selenion, and tellurium; oxygen, which is the first member of the group, to some extent summarises the properties of both families, but at the same time it differs from all the other members of the group. At the same time the elements of Group VI. taken as a whole more closely resemble one another than they resemble any other elements.

423 If we now turn to Group V. we shall find a group of ten elements shewing a gradation of properties from the first to the last member; we shall find that the group-character preponderates over the family-character, so that although the evenseries members are on the whole more like each other than they are like the odd-series members, yet it is not possible to divide Group V., as we have divided Group VI., into two distinct sub-groups or families.

The molecular weight of nitrogen is 28-02; the molecular weights of the other elements are unknown. Sp. grs. (approx.) .97 if air=1; 5.5 7 (?)

liquid; s.G.="885

The melting points of most of these elements have not been determined.

In a few minerals, not widely distributed, chiefly as oxides and sulphides.

Atom trivalent molecules.

* There is some doubt whether the body known as didymium is or is not a mixture of two or more elements; many of the properties of compounds of didymium are probably the properties of mixtures.

Appearance, and general physical properties.

General chemical properties.

425

Many phos-
phates occur
very widely dis-
tributed in
rocks and
waters; also in
bones and in
parts of plants.
Compounds of
P with C, N, and
O occur in nerve
and brain
matter.
Prepared by
heating
Ca(PO3)2 with
charcoal.

Soft wax-like
solid.
Crystalline.
Non-conductor
of electricity.

Burns in air to
P20 and P205.
Combines di-
rectly with Cl,
Br, and I.
Oxidised by
HNO3.
Does not form
salts by inter-
acting with
acids.
Hydride, PH3,
resembles NH
but is less alka-
line.
Oxides are
anhydrides.
Atom trivalent
and pentavalent
in gaseous
molecules.
Phosphorus
shews allotropy
(s. Chap. XI.,
par. 220).

500° (under
pressure)

13.2

*083

As2O3 and
As2S3 occur;
also compounds
of As with Te
and S, with Ni,
Co, &c. occur in
small quantities
widely distri-
buted.
Prepared by
heating As2O3
with charcoal.

Grey, hard,
brittle, solid.
Crystalline.

Fair conductor
of electricity.

18

⚫053

Chief naturally
occurring com-
pound is SbSg;
found in com-
paratively small
quantities in
very various
parts.
Prepared by
heating Sb2O3
with charcoal.

not determined.
Er2O3 occurs in
small quantities
in ytterbite, a
Swedish min-
eral.

*0308

Bismuth is found native; also Bi203 and BigS, &c., but not in large quantities.

Metal not yet Prepared by

obtained.

heating Biog

with charcoal.

Grey, with faintly reddish tinge; crystallises easily; brittle.

Bad conductor of electricity. Burns in air to Bi2O3. Combines directly with Cl, Br, and I. Oxidised by HNO3, and at same time Bi.3NOg is formed. Many salts known derived from acids. No hydride known.

Oxides are basic; Bi205 shews very slight acidic functions. Atom trivalent in gaseous molecules.

General formulae and chemical characters of compounds of elements of Group V.

Hydrides. MH,; M = N, P, As, Sb.

3

Oxides. MO; M=N, V. M,O,; M = N, V, Nb, Bi.
M2O3
M = any metal of the group except Nb and Ta. M ̧O;
M=N, P, V, Nb, Sb, Ta, Bi. M2O,; M = any element of the

2

group except Er. Hydrates of many of these oxides are

known.

Sulphides. No sulphides of niobium or erbium have yet been prepared. M,S,; Many element of the group except N, Ta, (Nb or Er). M,S,; M = P, V, As, Sb. A few other sulphides are known, e.g. N,S,, Ta,S

Haloid compounds. No haloid compounds of erbium have yet been prepared; the haloid compounds of nitrogen are very unstable and explode with great violence, their composition is still doubtful.

5

MX,; Many element of the group except Ta (? N) or Er. MX,; M÷P, Nb, Sb, Ta; X = Cl and in some cases also Br or I. A few other haloid compounds exist, e.g. PI VCI.

2

Acids. The following are the chief compounds of hydrogen with oxygen and an element of Group V. which are acids (when Aq is added to a formula it indicates that the acid is known only in aqueous solution).

4 2

HNOAq, HNO, Aq, HNO. H,PO,Aq, H.PO,Aq, H.PO,
HPО, HP, HVO„,
HVO, HVO HASO, Aq, HASO,
HASO, HAS,O,.
HAS, HSbO Hsbo H.sbo, HSb,O,.
H1Ta ̧О.

ვა

2 3

3

Salts. The only elements of the group which are known to form series of definite salts by replacing the hydrogen of acids are vanadium, didymium, erbium, and bismuth. The salts of vanadium are all basic salts, they belong for the most part to the series VOX and (VO),X; the salts of didymium and erbium belong to the series M,3X; the normal salts of bismuth belong to the series Bi̟,3X, but besides these a great many basic salts exist. (X=SO, 2NO, &c.). Antimony forms a few compounds which may be regarded as basic salts, especially xSb,O,.ySO, and xSb,O,.yN,O,; tartar-emetic, KSьCHO,, is probably to be classed as a double antimonypotassium salt.

The following are the principal compounds of elements of 426 Group V. which have been gasified, and the relative densities of the vapours of which have been determined; NH„, PH„, ASH, PCI, PI, PF, VCI, AsCl, AsI, NbCl,, SbCl, Sbl, TaCl, BiCl. The statements made in the table in par. 424 regarding the valencies of the atoms of the elements of Group V. are based on the existence and compositions of these gaseous molecules.

Arsenious and antimonious oxides have been gasified; the