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The ends of elements

Nature Chemistry volume 5, pages 350352 (2013) | Download Citation

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When elements 117 and 118 are finally named, should these new members of the halogen and noble gas families receive names ending in -ium as IUPAC has suggested? Brett F. Thornton and Shawn C. Burdette look at the history of element suffixes and make the case for not following this recommendation.

Disputes surrounding the discovery and naming of the elements predates modern chemistry, and provide a fascinating history-of-chemistry primer. The longstanding use in English of elemental suffixes such as -ium, -ine and -on has been rather less controversial, however, and has received scant attention. As the discovery of superheavy elements extends the periodic table to the end of the seventh period, the origin, value and meaning of the suffixes becomes relevant.

The periodic table can be intimidating to new chemistry students: the table's form, seemingly misshapen, belies the systematic information contained within. Even without guidance, chemistry students will search for patterns in the table as we all excel at finding order in apparent chaos. One pattern that immediately appears is in the element-name suffixes (Fig. 1), but this order breaks down on further investigation. Students soon realize that some elements possess mismatched names and symbols, such as gold (Au) and silver (Ag). Other elements also have pattern-breaking suffixes or no suffix at all. Why is element 74 not tungstenium like ruthenium or, tungstum like lanthanum? (The name tungsten comes from the Swedish words tung and sten, translating directly to heavy stone, and is the only English element name derived wholly from Swedish.) These examples and other named elements with unique and anomalous nomenclatures have all been known for more than 220 years; a few such as iron, gold and copper have been known and named as 'substances' since before the notion of an element existed.

Figure 1: The English names of the chemical elements as of the end of 2012.
Figure 1

There are 81 elements (grey) that end in the suffix –ium or –um, which is derived from Latin and denotes a metallic substance. There are two classes of elements that have the suffix –on; the noble gases Ne, Ar, Kr, Xe and Rn (orange) and the solid non-metals C, Si and B (green). The five halogens (pink) all end with –ine and there are three elements that have the suffix –gen (blue), which derives from the Greek meaning 'former', for example, hydrogen means 'water former'. The elements that end with either –ine or –gen are all diatomic molecules in their native form. That leaves 17 elements (sandstone) that have no suffix: no element without an identifiable suffix in English was discovered after 1783 (tungsten).

The modern concept of an element appeared in Antoine Lavoisier's seminal 1789 Traité Élémentaire de Chemie, building on an earlier 1787 work by Guyton de Morveau, Lavoisier, Claude-Louis Berthollet and Antoine François Fourcroy. The quartet's Methode Nomenclature Chimique had proposed reforming the haphazard chemical nomenclature of the past1; the preface to Lavoisier's text expounded further on the importance of good chemical nomenclature as well as names that made sense. Lavoisier, quoting the Swedish chemist Torbern Bergmen, wrote2: “[S]pare no improper names; those who are learned, will always be learned, and those who are ignorant will thus learn sooner.”

Over two centuries later, of 114 named elements, only the 17 that were known and named before 1784 have no discernible suffix or suffix pattern. In contrast, every metallic element discovered in the past 220 years has been given either an -ium or, less frequently, an -um suffix. Every non-metal and metalloid discovered since 1788 has either an -on or -ine suffix, except helium and selenium.

Selenium was discovered as a byproduct of sulfuric acid production and named around 1817 by Jöns Jacob Berzelius3. Berzelius identified selenium as a metal because of its appearance3, although today it is considered a metalloid. Helium was spotted in the solar spectrum in the 1860s and named shortly thereafter as a metal, without any knowledge of its chemistry4. When helium was isolated from uranium ore decades later, the name was preserved, despite its non-metallic properties5. Synchronizing helium with the nomenclature of the noble gas family has been proposed; the name helion was repeatedly suggested, but never adopted6,7,8,9.

The periodic table is dominated by metals, and the majority of them use the -ium suffix. The -um suffix of elements like platinum derives from the Latin suffix for metals, as seen in ferrum (iron), aurum (gold) and argentum (silver), among others. The motivation and reason that -um morphed into -ium is unclear, but the practice emerged in metallic elements named in the early nineteenth century. For example, although British chemist Humphrey Davy chose the name aluminum, an 1813 book review of Davy's 1812 Elements of Chemical Philosophy suggested the name sounded too “classical”, and proposed aluminium instead10. Aluminium was adopted by most of the world, including the United Kingdom, whereas Davy's original version stuck in the United States.

Two groups of non-metallic elements use the -on suffix; the larger group being the noble gases. Naming of the noble gases was dominated by one man, William Ramsay, who was involved in the discovery of four noble gases and in suggesting names for five. He recognized the importance of the task11: “The naming of a new element is no easy matter. For there are only twenty-six letters in our alphabet, and there are already over seventy elements. To select a name expressible by a symbol which has not already been claimed for one of the known elements is difficult, and the difficulty is enhanced when it is at the same time required to select a name which shall be descriptive of the properties (or want of properties) of the element.” Of particular note, Ramsey emphasized “[D]escriptive of the properties of the element,” which echoes Lavoisier's opinion from over a century earlier.

“Every metallic element discovered in the past 220 years has been given either an -ium or, less frequently, an -um suffix.”

In 1894, argon became the first noble gas discovered on Earth12. The name suggested by H. G. Madan referenced argon's inert nature and was derived from Greek words meaning idle or lazy13. Ramsay's son suggested novum, from the Latin word for new, for the next similar gas discovered13, but Ramsay realized these might be members of an entire new family of elements14. With that thought, the name neon was chosen using the Greek word for new and adopting the -on suffix used for argon15. Linguistically the -on suffix in neon, argon12, krypton15 and xenon originates from transliterations of Greek adjectives; however, radon was named to indicate its primary source (radium) with the addition of -on to match the other noble gases6.

Aluminium or aluminum? Image: © STUDIOSOURCE/ALAMY

Carbon, a non-metal known since antiquity, lent its last syllable (-on is not a suffix in carbon) to the chemically similar boron and silicon in a linguistic manoeuvre known as back-formation: the -on syllable was assumed to be a phoneme carrying the meaning 'element like carbon'. Humphrey Davy, believing he had a metal, originally used the name boracium in 1809 (ref. 16) but by 1814 he had revised the name to boron17. In a similar manner, Berzelius originally referred to silicon as silicium in 1823, but later the suffix was modified by Thomson who argued18: “[Silicon] has been usually denominated silicium. But as the termination um is used by chemists to denote metals, it is better to make carbon, boron, and silicon, which are not metallic, and which resemble each other closely, terminate in the same syllable on, already appropriated to carbon.”

Five existing halogens share a unique suffix found nowhere else on the periodic table. Whether it rhymes with wine or Wien (or even win), the -ine suffix uniquely identifies an element as a halogen. When Humphrey Davy named chlorine in 1810 from the Greek chloros for yellow–green, he was not completely convinced it was an element, but as it was definitely not metallic, he avoided the -ium suffix19,20. The discovery and naming of iodine21,22 and bromine23 followed, and even though they were named first in French, which omits any suffix for halogens, the names were soon amended with -ine suffixes in English24. The existence of fluorine was predicted long before it was isolated, and named using the system adopted for the halogen family25. The most recently named non-metal, astatine26, was named to match the lighter halogens27.

Research at the frontiers of the periodic table continues, and IUPAC endorsed names for elements 114 and 116 in 2012 (ref. 28). There are claims for the discovery of elements 113 (ref. 29), 115 (ref. 29), 117 (ref. 30) and 118 (ref. 31). As these have yet to be accepted by IUPAC, these elements retain their temporary systematic names, such as ununoctium. Some proposals for these systematic names would have given us ununseptine and ununocton for elements 117 and 118 respectively32, but will elements 117 and 118 gain the -ine and -on suffixes of their lighter congeners — and should they?

IUPAC first specifically addressed element suffixes in 1953, by stating33 “new metallic elements should be given names ending in -ium”. This is a reasonable, historically supported decision because the eight metals lacking the -ium or -um suffix were discovered 225 or more years ago. For non-metals and semi-metals, there have never been any official guidelines about suffix choices. With history for guidance, no non-metal or metalloid has been given the -ium suffix except for selenium and helium — and those two exceptions were believed to be metals when they were named.

Despite these strong historical precedents, the 2002 IUPAC naming guidelines is the earliest and only reference to state34 “For linguistic consistency, the names of all new elements should end in '-ium'.” The only rationale provided by IUPAC for choosing -ium has been “linguistic consistency”. If non-metals generally adopt non-ium suffixes, the selected names for elements 117 and 118 should consider the elements' physical and chemical properties. Predictions about the properties abound, especially concerning whether or not element 118 is a noble gas35,36, but these elements only exist fleetingly in particle accelerators.

Although methods for analysing the chemical properties of elements 117 and 118 have been proposed37, a lack of chemical knowledge will not stop the naming process. IUPAC's present recommendation does not consider the properties of the element as a factor in the form of its name34. Though future chemists and students would be best served by nomenclature choices based on chemical properties, this is not the current plan. Worse yet, the current guidelines ignore historical precedent, as well as the use of element names as a tool in explaining chemistry. Linguistic consistency would seem to support using -ine for halogens and -on for noble elements.

For more than 140 years -ium has been applied exclusively to metallic elements, whereas halogens and noble gases have been given -ine and -on suffixes respectively. Despite elements becoming increasingly metallic lower in the periodic table, the use of -ium for new halogens or noble gases would not be based on established chemical principles or historical precedent, perhaps leading to linguistic confusion and educational difficulties.

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  1. Brett F. Thornton is in the Department of Geological Sciences (IGV) and Bert Bolin Centre for Climate Research, Stockholm University, 106 91 Stockholm, Sweden

    • Brett F. Thornton
  2. Shawn C. Burdette is in the Department of Chemistry and Biochemistry, Worcester Polytechnic Institute, Worcester, Massachusetts 01609-2280, USA

    • Shawn C. Burdette

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