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

Tellurium does not exist in more than one form; the acids H.Tel, 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. Te0,.2HCl is known); some of the physical properties of tellurium approximate to those of the metals.

The existence of the stable gasifiable tetrachloride Tecl, ; the formation not only of ditellurates MTe,, but also of tetratellurates MTe , 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.

OXYGEN is the first member of the even-series of the group 421 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 H O and hydrogen peroxide H,O,, 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.

The compounds of oxygen with chlorine CIO, and (?) CIO, do not resemble the chlorides of the other members of Group VI. in composition, but the oxide OCI, is analogous in composition to MCI, when M = S, 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 0,,, Se, and Sex, S, and Sc, emphasises the resemblance between oxygen, sulphur,

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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.

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12

424

8

10 (Even series. N=14.01 V=51-2 Nb= 94 Di=144 Ta=182 Group v. 1 35

9

11 Lodd series. P=30-96 As=74:9 Sb=120 Er=166 Bi=208 Even-series NITROGEN. VANADIUM. NIOBIUM. DIDYMIUM*. TANTALUM.

elements Atomic weights 14.01

51.2

144

182 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 (?)
6:5(?)

11 (?) liquid ; s.G.=.885 Sp. heats

not determined. not determined. *0456 not determined. Atom, weights

9.3
13.4 (3)
22:3 (?)

165(?) spec. gravs.

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

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Occurrence and In large quanti- In a few minerals, not widely distributed, chiefly as oxides and sulphides. preparation. ties in air.

Prepared by Prepared by Prepared by Prepared by Many com

. long continued heating NbC1, heating Dicly heating pounds, especi- he

peci heating VCl2 in repeatedly in with potassium; K TaFy with ally ammonia

hydrogen. hydrogen. or by electrolys- potassium. and nitrates,

ing molten
also occur in

DiCiz.
large quantities
and widely dis-
tributed.
Prepared by
removing 0

from air. Appearance, and Colourless, Grey, crystal Steel-grey, lus- White solid Grey, lustrous, general physical tasteless, odour. line, powder. trous, solid. with slightly solid; not yet properties. less, gas.

yellow tinge. obtained apLiquefied at

Ductile, hard. proximately very low tem

pure.
perature and
under great
pressure; liquid
boils at abt.

- 1950 General chemical Combines di- Burns in air to Burns in air to Burns in air to Burns in air to properties. rectly with few V90, then V203, Nb205.

Di,03.

Ta205. if any elements and finally combines di- Oxides seem to combines diat ordinary V205. Burns rectly with Cl to act only as rectly with CI temperatures; in či to VC14. form NbC1z. bases; Di,05 to form TaC15. but at very Combines di Dissolved by acts as a per- Dissolved only high tempera- rectly with N conc. H2SO4 not oxide.

by conc. HFAQ tures combines forming VN. by HCIAğ or No compounds or by mixture directly with B, Dissolved by HNO3Aq. have been of H2SO4A9 Si, Cr, Mg, V, conc. H2SO4, Nb205 is an an- gasified.

and HFA. and a few other and HNO3A. hydride.

No hydride Ta205 is an anelements. Molten alkalis Salts of Nb are known.

hydride, and has If electric dis- forni vanadates. not known but

apparently no charge is passed Some oxides are the subject has

basic properties. through mix basic, others are not been

No hydride ture of N with basic and also thoroughly in

known.
0, or H, a very acidic.
vestigated.

Atom pentavalittle NÓ., or. V acts both as a No hydride

lent in gaseous NH, is formed. metallic and a known with cer

molecules. Strongly nega- non-metallic tainty. element.

Atom pentavaOxides are gene No hydride lent in gaseous rally anhy known.

molecules.
drides.

Atom is tetra-
Hydride, NH,, (and perhaps
is strongly alka- also tri-) valent
line.

in gaseous
Atom trivalent molecules.
in gaseous

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.

tive.

45°

18

202

Odd-series PHOSPHORUS. ARSENIC. ANTIMONY. ERBIUM.

BISMUTH. elements Atomic weights 30-96

74.9

120
166

208 Molecular weights 123.84 and 61.92 299-6 and 149.8 2360 or 240

unknown Sp. grs. (approx.)

507
67

9-9 Melting points

500° (under
430°

270° (approx.)

pressure) Atomic weights

16.3
13.2

20:5 spec. gravs. Sp. heats

*083
053 not determined.

*0308 Occurrence and Many phos As,03 and Chief naturally Er,0occurs in Bismuth is preparation. phates occur AS S3 occur; occurring com- small quantities found native;

very widely dis- also compounds pound is Sb2S3; in ytterbite, & also Bi,03 and tributed in of As with Te found in com- Swedish min Bi,S3, &c., but rocks and and S, with Ni, paratively small eral.

not in large waters; also in Co, &c. occur in quantities in

quantities. bones and in small quantities very various Metal not yet Prepared by parts of plants. widely distri parts.

obtained.

heating BigOg Compounds of buted. Prepared by

with charcoal.
P with C, N, and Prepared by heating Sb2O3
O occur in nerve heating As20, with charcoal.
and brain

with charcoal.
matter.
Prepared by
heating
Ca(PO3)2 with

charcoal.
Appearance, and Soft wax-like Grey, hard, Grey, lustrous,

Grey, with general physical solid. brittle, solid. brittle, very

faintly reddish properties. Crystalline. Crystalline. crystalline,

tinge; crystalNon-conductor Fair conductor solid.

lises easily; of electricity. of electricity. Fair conductor

brittle. of electricity.

Bad conductor

of electricity. General chemical Burns in air to Burns in air to Burns in air to Oxide, Er,0, is Burns in air to properties. P203 and P205. As203.

basic, forming Bi203. Combines di- Combines di- Combines di- salts, e.g. Combines directly with Cl, rectly with CI, rectly with CI, Er,3804.

rectly with C1, Br, and I.

Br, and I, Br, and I. No hydride Br, and I.
Oxidised by Oxidised by Oxidised by known.

Oxidised by
HNO3.
HNO..
HNO3.

No oxide known HNO3, and at Does not form No salts known A few salts de- to act as an an- same time salts by inter- derived from rived from acids hydride.

Bi.3 NO, is acting with acids.

seem to exist. No compound formed. acids.

Hydride, AsH3, Hydride, SbHg, yet gasified. Many salts Hydride, PH3, is scarcely if at not alkaline.

known derived resembles NH, all alkaline. Oxides are

from acids. but is less alka- Oxides are anhydrides, but

No hydride line. anhydrides. also slightly

known. Oxides are Atom trivalent basic.

Oxides are anhydrides. in gaseous Atom trivalent

basic; Bi.03 Atom trivalent molecules. in gaseous

shews very and penta valent Arsenic exists molecules.

slight acidic in gaseous in allotropic

functions. molecules. forms (s. "Chap.

Atom trivalent Phosphorus XI., par. 222).

in gaseous shews allotropy

molecules. (8. Chap. XI., par. 220).

Sb2O3:

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

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

Oxides. M,0; M =N, V. M,0,; M = N, V, Nb, Bi. M0,g; M=any metal of the group except Nb and Ta. MO; M= N, P, V, Nb, Sb, Ta, Bi. M,05; M = any element of the

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group except Er. Hydrates of many of these oxides are known.

Sulphides. No sulphides of niobium or erbium have yet been prepared. M.S; M = any 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. Ns, 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.

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

Àcids. 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).

HNOAq, HNO, Aq, HNO, H PO, Aq, H,PO,Aq, H PO, HPO, HBO, HVO, HVO. ?H AsO, Aq, HÅSO, HAO, HASO, H Sbo, Hsbog, H.SbO, H.86,0, HTa o.

*Sålts. 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 Bi 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 Sb 02YSO, and 2Sb 02. YN 05; tartar-emetic, KSC,H,O,, is probably to be classed as a double antimony. potassium 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, Sb, 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

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