A systematic way of naming chemical substances

As new substances were discovered or synthesized in the past their names may have been related to the natural substance or place they were derived from. For example, oil of wintergreen and Epsom salts Or they may have been named according to the use they were put to (e.g. washing soda crystals), or the person who first discovered the substance (e.g. Vaska’s compound1) or a variety of other reasons. As more and more compounds were discovered or synthesized it became more and more difficult to remember all their names as there was no systematic logic behind them.

In 1919 the International Union of Pure and Applied Chemists (IUPAC) was formed. IUPAC is an international, non-governmental body made up of chemists from both academia and industry. The aim of IUPAC is to fostering worldwide communication in chemistry. Currently about one thousand chemists throughout the world are engaged on a voluntary basis working for IUPAC. One of their greatest achievements has been to bring in a logical and accepted way of naming compounds. IUPAC of course is a great example, perhaps the best example, of the International Dimension in Chemistry. The use of IUPAC nomenclature, formerly known as the Stock-naming system for inorganic compounds, makes much use of oxidation numbers. An oxidation number is the same as an oxidation state except that the sign is omitted and the number is written in Roman numerals. Since this is the TOK section it is worth noting that oxidation numbers do not actually exist. Atoms or ions do not go around with their oxidation number stamped on them! Oxidation states are a man-made concept and in fact wrong assumptions, such as covalent compounds being assumed to be ionic, are made in order to assign oxidation states.

Thus in the past what was known as cupric sulfate, CuSO4 now becomes copper(II) sulfate and is easily distinguishable from copper(I) sulfate, Cu2SO4, which used to be known as cuprous sulfate. In theory all inorganic compounds should include the oxidation number but for elements that only have one common oxidation number it is omitted, e.g. potassium nitrate is not called potassium(I) nitrate. Many simple compounds also still retain their old name so that, for example, ammonia is still known as ammonia not nitrogen(III) hydride and water is not hydrogen(I) oxide. Although IB Diploma Chemistry, along with other examination boards, tends to have adopted the IUPAC way of naming substances there are still many exceptions and in the wider world non-chemists (and some chemists!) still often use common names so there is still some confusion over naming.

Some examples of different chemical names still in use

IUPAC nameCommon nameFormula
sulfate(VI)sulfate (or sulphate)SO42
sulfate(IV)sulfite (or sulphite)SO32
iron(II) chlorideferrous chlorideFeCl2
iron(III) chlorideferric chlorideFeCl3
sodium hydrogencarbonatebicarbonate of sodaNaHCO3
ethanoic acidacetic acidCH3COOH

It is tempting to compare how IUPAC works to some governmental agencies such as the Académie française (French Academy). The Académie française was founded in 1635 by Cardinal Richelieu and revived by Napoleon Bonaparte in 1803 after it was suppressed during the French revolution. Its function is to decide how the French language should be used. Chemists generally accept IUPAC but the mass of the people tend to ignore this and still tend to impose their own way of using words. Shops worldwide still stock ‘white spirit’, ‘vinegar’, ‘washing soda crystals’ and ‘baking powder’. Meanwhile in France, in a similar way, many people ignore the dictat of the Académie française and use ‘le weekend’ and ‘le football’.


1 trans-chlorocarbonylbis(triphenylphosphine)iridium(I), IrCl(CO)(PPh3)2

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