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142 BEFORE proceeding further with the examination of the
properties of classes of elements and compounds with the view of tracing connexions between changes of composition and changes of properties we must acquaint ourselves with the system of nomenclature used in chemistry.
Many names of elements, and such names of classes of compounds as oxides, hydrides, &c. have been incidentally
employed. 143 A name is given to each element. Sometimes the name
expresses a characteristic chemical or physical property of the
Some names are purely fanciful; e.g. tellurium, selenion, uranium, vanadium, (from tellus = the earth, pelnun = the
moon, the planet Uranus, and the Scandinavian deity Vanadis, respectively). The names of the more recently discovered metals all end in um.
The name given to a compound expresses the qualitative 144 composition of that compound ; if more than one compound of the same elements is known, names are given indicative of the relative quantities of the elements which unite to form reacting weights of the compounds.
The name of every compound of two elements ends in ide. Thus all compounds of oxygen with one other element are called oxides. The variety of oxide is indicated by prefixing the name of the element united with oxygen; thus we have iron oxides, zinc oxides, sulphur oxides, &c.
Similarly we have sulphides, i.e. compounds of sulphur with one other element; chlorides, i.e. compounds of chlorine with one other element; bromides, fluorides, hydrides, &c. &c. We say hydrogen oxide, hydrogen chloride, hydrogen sulphide; not oxygen hydride, chlorine hydride, sulphur hydride: oxygen, chlorine, and sulphur, are all more negative, or more nonmetallic, elements than hydrogen. The name of the more negative of the two elements of a binary compound is changed into a qualifying term ending in ide. Thus it is better to say oxide of chlorine-or chlorine oxide—than chloride of oxygen (or oxygen chloride).
When two oxides, chlorides, &c. of one element are known, the general custom is to form an adjective from the name of the element other than oxygen, &c. and to modify the termination of this adjective so as to express that one compound is composed of more, or less, oxygen, relatively to a fixed mass of the other element, than the other compound is. A comparison of the following names with the composition of each compound as expressed by its formula will illustrate this method of naming pairs of oxides, &c. of the same element. Iron oxides
Sulphurous oxide SO,
The termination -ous always indicates less of the nonmetallic or negative element than the termination -ic, relatively to the same mass of the metallic or positive element.
When more than two oxides, &c. of the same element are known, two methods of naming are adopted. Four oxides of bismuth are known. Their compositions, and the names given to each, are as follows :
Hypobismuthous oxide; or Bismuth dioxide ..
Nitric oxide . . . .
Nitrogen pentoxide . . NO. One oxide gets the termination-ic; another, with relatively less oxygen, the termination -ous; the prefix hypo- is used to express relatively less oxygen than that of the -ic or -ous oxide. The prefix per- is sometimes employed to designate that oxide of a series which has relatively most oxygen.
Or the number of combining weights of oxygen in a reacting weight of each oxide is expressed by the prefixes mono, di, tri, &c. Unfortunately neither system is very strictly carried out. We shall have further examples of each system as we proceed.
The composition of one oxide of a series is sometimes expressed by a name formed from the names of other two oxides of the series ; thus FeO is ferrous, Fe, O, is ferric, and Fe, O, is ferroso-ferric, oxide.
The name sesquioxide is frequently used; it implies that a positive element and oxygen are united in the ratio of 1:11 combining weights ; thus Fe,0, is often called iron sesquioxide, Cr O, chromium sesquioxide, &c.
Acidic oxides are sometimes named so as to indicate the acid obtained by interaction of each with water; thus SO, is called sulphuric anhydride, because it interacts with water to produce sulphuric acid. On this system of naming, the term anhydride means an acidic oxide. Lastly an oxide, chloride, &c. is sometimes distinguished from another oxide, chloride, &c. of the same element by a term indicating some prominent physical character, usually colour; thus one sometimes speaks of the brown oxide of chromium, the black, or the magnetic, oxide of iron.
The various systems of naming binary compounds are summarised in the following examples.
Sulphur oxides. so, Sulphurous oxide; Sulphur dioxide ; Sulphurous anhydride.
So, Sulphuric oxide; Sulphur trioxide; Sulphur peroxide;
* Cro Chromic oxide; Chromium sesquioxide; Green oxide of chromium.
CrO. Chromium dioxide; Brown oxide of chromium.
Cro Chromium trioxide; Chromiumi peroxide; Chromic anhydride ; Red oxide of chromium.
The nomenclature of many compounds of three or more 145 elements is based on the relations which exist between acids and salts. To each acid is given a name indicative, as far as possible, of its composition. Prefixes and terminations are used as in the naming of binary compounds. Thus all acids obtained by combining sulphur with hydrogen and oxygen are called sulphur acids; those formed by the combination of chlorine with hydrogen and oxygen are called chlorine acids ; those produced by uniting nitrogen with hydrogen and oxygen are called nitrogen acids; and so on.
The following examples shew how one acid is distinguished
H PO, Phosphorous
The three acids H PO, HPO,, H.P.0, are all called phosphoric acid because they are all obtainable from the same oxide or anhydride, P.Os. The composition of the acid formed by the interaction of this oxide with water varies according to the relative masses of the interacting compounds, and the temperature; thus
P,O, +HO (cold) = 2HPO,
(3) POŚ+3H 0 (hot) = 2H PO.
That acid of the three from which the greater number of well known and stable salts are obtained, viz. H PO, is called orthophosphoric acid (ópoos = right or true); the acid HPO, may be obtained from H PO, by removing water (H PO.-H,O=HPO), it is generally called metaphosphoric (metà implies change of composition); the third acid H PO, may be produced by heating H, PO, (2H,PO, heated = 1,8,0, +H,O), it is called pyrophosphoric acid.
The names of the salts obtained from a given acid by causing
Sulphuric acid; H SO,
Iron nitrates. .
Fe3NOFerric , These examples shew the use of the adjectival form of the name of the metal, and the meaning of the terminations ous