Inorganic compounds

Nomenclature





Nomenclature for salts

Salts consists of positively and negatively charged ions. In the systematic naming of these, you usually name the positive ions first, followed by the negative ions. The sequence for the positive and negative ions, if there is more than one, is often a matter of history and fairly random, but as a general rule, you sort them according to placement in the periodic system.

Cooking salt and baking soda are thus:

NaCl = sodium + chloride = sodium chloride
NaHCO3 = sodium + hydrogen + carbonate = sodium hydrogen carbonate

If you can have more than one ratio for the ions, the ratio is a part of the name, e.g.:

KH2PO4: Potassium dihydrogen phosphate
K2HPO4: Dipotassium hydrogen phosphate

If the metal ion can have multiple oxidation steps, the oxidation step is mentioned in the name:

Hg2O: Mercury(I) oxide, pronounced mercury-one-oxide
HgO: Mercury(II) oxide, pronounced mercury-two-oxide
FeO: Iron(II) oxide, pronounced iron-two-oxide
Fe2O3: Iron(III) oxide, pronounced iron-three-oxide


Negatively charged ions, consisting of only one element, are usually given the ending -ide, e.g.

SiC: Silicon carbide
NaF: Sodium fluoride

you should however be aware, that a few deviations are found when the element can have multiple oxidation steps. The most common is peroxide, which most people know from hydrogen peroxide H2O2.


For the polyatomic ions, naming becomes a semisystematic combination of common names. If you look at the combination chlorine + oxygen, with chlorine i four different oxidation steps:

ClO: hypochlorite
ClO2: chlorite
ClO3: chlorate
ClO4: perchlorate

we have the similar names for bromine:

BrO: hypobromite
BrO2: bromite
BrO3: bromate
BrO4: perbromate

so the common names are systematic to some extent.

The prefix per is used to signify something which is more oxidized than the reference. Perchlorate, ClO4, which i more oxisized than chlorate, ClO3, persulfate, S2O82−, which is more oxidized than sulfate, SO42−, etc. There is no specific oxidation step or ratio in the prefix, it only means that the oxidation step here is higher than for the reference ion.

The prefix pyro is used for 2 ions of the same type that are connected. Pyro is mostly used in connection with phosphates and sulfates, pyrophosphate, P2O74− and pyrosulfate, S2O72− respectively, as they are highly relevant in biology, but other types, e.g. pyrovanadate (V2O74−), can be found.

If the salt contains crystal water, you add number + hydrate to the name, e.g. CuSO4·5 H2O: copper-two-sulfate, pentahydrate and CaSO4·2H2O: calcium sulfate, dihydrate (calcium in compounds only occur in oxidation step +2, so here the number 2 is implied).

If the salt is found in several crystal structures, this is also seen in the naming, but this requires that you know the terminology for the salt at hand. Here you usually use common names or prefixes, with no mentioning of the crystal structure. It could be something like TiO2 which is found as anatase (tetragonal crystal structure), rutil (tetragonal ditetragonal dipyramidal crystal structure), and brookit (orthorhombic crystal structure). The names can also reflect the morphology of the crystal, e.g. scalenohedral and cubic calcium carbonate that both have a trigonal crystal structure. Therefore, contrary to what you may be led to believed, the names do not reflect the crystal structure.



Nomenclature for minerals

Minerals is a somewhat special section of the naming of inorganic compounds. For the natural minerals, common names are used, referring to a composition, crystal structure and, to some extent, where they are found in nature. There is a systemt in the naming, to some degree, as you have groups of minerals, e.g. cyclosilicates and apatite, containing one or more functional groups in a specific constellation, but you should not take the naming as more than a general indication of what to expect for the mineral's formula.

In regards to minerals, it is especially important to be aware, that names are not unambiguous. Dolomite is CaCO3 where Mg is inserted in the crystal structure, usually written as (Ca·Mg)CO3 or CaMg(CO3)2, with no specification of the ratio. You could be led to believe that the Ca:Mg ratio is 1:1, and you can find references to the existence of such a mineral. But, for the most common dolomite, the formula is around Ca0.62Mg0.38CO3 while in the sea algea Goniolithon the ratio is around Ca0.77Mg0.23CO3.



Nomenclature for metals and alloys

Nomenclature for the pure metals is usually just the name of the element, e.g. gold and silver. There is however metals, that can be found in multiple crystal structures. Here you add a prefix to the element, if you know which type you have. This is usually the color or alpha, beta, etc. In a few cases, like alpha-arsenic/grey arsenic, you have both prefixes.

For alloys you usually specify metal types and ratio, e.g. Nitinol 60, which is a nickel/titanium alloy having 40 % nickel and 60 % titanium. Systematic naming is not used, but you have names referring to combinations, e.g. Nitinol and stainless steel, followed by a number that specifies the ratio in the alloy's mixture. Some alloys are only loosely defines, e.g. bronze which is 95 % copper, 4 % tin and 1 % zinc if it used for coins, but 88 % copper, 16 % tin and 2 % zinc if used for bronze bearings, so here you should be aware of differences in composition.

As with the pure metals, the crystal structure of the alloy is important for the material properties, which is why you talk about e.g. austenitic steel, which is cubic face centered, contrary to e.g. ferritic steel, cubic body centered. The crystal structure is thus not explicitly mentioned in a systematic name but lies implicitly in the common name.