Most elements end in -ium because Latin was the international language of science when the majority of elements were discovered, and metals in Latin traditionally received names ending in -um or -ium. That convention became so deeply embedded in chemistry’s culture that when the field’s governing body, the International Union of Pure and Applied Chemistry (IUPAC), wrote formal rules for naming new elements, it codified the -ium suffix as the default for the vast majority of the periodic table. The story behind this seemingly small detail runs through centuries of naming fights, a handful of stubborn exceptions, and at least one noble gas that got the wrong ending and kept it anyway.
Latin and the Language of Early Chemistry
Long before anyone had a periodic table, the metals known to the ancient world already carried Latin names. Gold was aurum, silver was argentum, iron was ferrum, copper was cuprum, lead was plumbum, and tin was stannum. These names all end in -um, the standard Latin suffix for neuter nouns, and they became the root of the chemical symbols still used today (Au, Ag, Fe, Cu, Pb, Sn). Because Latin served as the shared language of European scholars from the medieval period through the Enlightenment, any new substance described in a scientific treatise received a Latin-style name almost by reflex.
When 18th-century chemists started isolating new metallic elements at a rapid pace, they reached for the same linguistic toolkit. A newly separated metal felt like it belonged alongside the classical metals, so giving it a name ending in -ium was the natural move. The suffix subtly signaled “this is a metal” to anyone reading the publication. Barium, calcium, strontium, magnesium, aluminum: all of them acquired their -ium endings during this wave of discovery, and the pattern became self-reinforcing. Each new -ium name made the next one feel more inevitable.
Naming Battles in the Age of Electrolysis
The early 1800s were a golden age of element discovery, and with it came fierce debates about what to call the new substances. Humphry Davy’s isolation of potassium and sodium through electrolysis in 1807 is one of the most famous episodes. Davy initially proposed “potassium” and “sodium” for the English-speaking world, but scholars on the European continent preferred “kalium” and “natrium,” which is why the symbols K and Na persist on every periodic table. The evolution of these names involved genuine uncertainty about whether the newly liberated substances were even metals in the traditional sense, and different naming preferences reflected different interpretations of their chemical nature.1Ambix. New Sources for Reconstructing the Discovery of Potassium and Sodium
What matters for the -ium question is that in every case, once a substance was confirmed to be a metal, it got an -ium ending in at least one major language tradition. Davy’s potassium already had it. Continental Europe’s kalium had it. When the Swedish chemist Jöns Jacob Berzelius cataloged elements in the early 19th century and pushed for systematic Latin names, -ium became the undisputed standard for metallic elements across borders. Since roughly three-quarters of all known elements are metals, the convention alone was enough to make -ium the dominant ending on the periodic table.
The IUPAC Rules That Made It Official
For most of chemistry’s history, the -ium convention was informal. Discoverers followed it because everyone else did, not because a rulebook required it. That changed in the early 2000s when IUPAC published formal recommendations for naming newly discovered elements. These rules, slightly amended over the years, specify that elements in groups 1 through 16 of the periodic table should receive names ending in -ium, while elements in group 17 (the halogens) get -ine and elements in group 18 (the noble gases) get -on.2Pure and Applied Chemistry. How to Naming New Chemical Elements
Groups 1 through 16 cover the overwhelming majority of the periodic table, including all the alkali metals, alkaline earth metals, transition metals, post-transition metals, metalloids, and even some nonmetals. So the IUPAC rule effectively guarantees that almost every element discovered from now on will end in -ium. The goal, as IUPAC itself puts it, is to maintain “historical and chemical consistency,” preserving the Latin-derived naming tradition that chemists have used for centuries.2Pure and Applied Chemistry. How to Naming New Chemical Elements
This formalization also helps with translation. Because -ium endings are recognizable across languages and alphabets, a physicist in Japan and a chemist in Brazil can both look at a name like “nihonium” and immediately recognize it as an element. The suffix works as a kind of universal flag.
Why Some Elements End in -ine or -on Instead
The three-suffix system reflects genuine chemical differences. The halogens, which sit in group 17, are reactive nonmetals that tend to exist as gases or volatile liquids under ordinary conditions. Their -ine ending traces back to the naming of chlorine in 1810 and was extended to fluorine, bromine, iodine, and astatine as each was discovered. When tennessine, the most recently confirmed halogen, was named in 2016, it received the same -ine ending in keeping with the IUPAC rules.2Pure and Applied Chemistry. How to Naming New Chemical Elements
The noble gases in group 18 get -on, a convention rooted in the naming of argon in 1894. Argon comes from the Greek argon, meaning “lazy” or “inactive,” and the -on ending echoed that Greek origin. Subsequent noble gases followed suit: neon, krypton, xenon, radon. The newest member of the group, oganesson, received its -on ending when it was named in 2016, even though oganesson is so unstable and short-lived that scientists have never been able to observe whether it actually behaves like a noble gas at all.
The Helium Problem
Helium is the most obvious oddity. It is a noble gas, so under IUPAC’s current rules it would receive an -on ending. But helium was discovered under unusual circumstances. In 1868, astronomers spotted an unknown spectral line in sunlight during a solar eclipse. They named the new substance “helium” after the Greek word helios, meaning sun, and gave it the -ium ending because they assumed it was a metal. There was no sample of the stuff on Earth yet, no way to test its properties, and metals were what people expected to find. When helium was finally isolated from uranium ore in 1895 and turned out to be an inert gas, the name had already been in use for nearly three decades. Nobody seriously proposed changing it.
This makes helium the only noble gas that ends in -ium. It is grandfathered in, essentially a fossil of a wrong guess preserved in the periodic table. IUPAC’s naming rules apply only to newly discovered elements, so they have no mechanism for retroactively renaming helium to “helion” even if anyone wanted to, which no one particularly does.
Elements That Predate the Convention Entirely
A number of familiar elements break the -ium pattern for the simple reason that their English names were inherited from older languages before Latin chemical naming took hold. Carbon, sulfur, phosphorus, nitrogen, oxygen, and hydrogen all received their names in the late 1700s from Greek or Latin roots that had nothing to do with the metal-naming convention. Oxygen, for instance, was named by Antoine Lavoisier from the Greek for “acid-forming.” Hydrogen comes from the Greek for “water-forming.” These names describe chemical properties, not membership in the metallic family, and they predate the era when -ium became a systematic expectation.
Then there are the truly ancient elements whose English names come from Germanic or Old English words. Gold, silver, iron, copper, tin, and lead all have everyday English names that bear no relation to their Latin chemical names. You would never guess from the word “lead” that its symbol is Pb, from plumbum. These elements were known for thousands of years before modern chemistry existed, and their names are culturally entrenched. The Latin -ium versions live on only in the element symbols and in certain compound names (like “cupric” or “ferrous”).
Altogether, roughly two dozen elements break the -ium pattern. Most of them are either nonmetals named before the convention solidified or metals known since antiquity whose common names in English just stuck. The rest of the periodic table, well over ninety elements, follows the -ium rule either because chemists chose the suffix voluntarily or because IUPAC mandated it.
Aluminum, Aluminium, and the Atlantic Divide
One of the more entertaining consequences of the -ium convention is the aluminum versus aluminium debate. Humphry Davy, who isolated the element, originally proposed “alumium” in 1808, then changed his mind to “aluminum.” Other British chemists preferred “aluminium” because it better matched the -ium pattern of sodium, potassium, and magnesium. North America stuck with Davy’s “aluminum,” while most of the rest of the English-speaking world adopted “aluminium.”
IUPAC officially recognized “aluminium” as the standard international name in 1990, but added “aluminum” as an acceptable alternative. This remains one of the only cases where an element has two accepted spellings in English, and the difference is entirely about whether -ium should apply consistently. The underlying chemistry is, of course, identical. The debate is purely about aesthetics and linguistic tradition. If you have ever wondered why some periodic tables show “aluminum” and others show “aluminium,” this is the reason: a 200-year-old naming disagreement that nobody has resolved and nobody particularly needs to.
How New Elements Get Their Names Today
The process for naming a new element is more regulated than most people expect. The team that synthesizes and confirms a new element gets the right to propose a name, but that proposal must pass through IUPAC’s Inorganic Chemistry Division for review. The proposed name can honor a scientist, a place, a property of the element, a mineral, or a mythological concept. It cannot honor a living person other than a discoverer, and it must end with the correct suffix for the element’s position on the periodic table.2Pure and Applied Chemistry. How to Naming New Chemical Elements
The four most recently named elements illustrate the range of inspirations:
- Nihonium (113): named after Nihon, a Japanese word for Japan, by its discoverers at RIKEN.
- Moscovium (115): named for Moscow Oblast, where the Joint Institute for Nuclear Research is located.
- Tennessine (117): named for Tennessee, home to Oak Ridge National Laboratory. As a group 17 element, it received -ine rather than -ium.
- Oganesson (118): named after nuclear physicist Yuri Oganessian. As a group 18 element, it received -on.
Before a name is finalized, IUPAC opens a five-month public comment period. Once approved, the name is permanent. No element has ever been officially renamed through the IUPAC process. The entire pipeline, from synthesis to confirmed naming, often takes a decade or more because the initial synthesis must be independently verified before naming even begins.
Temporary Placeholder Names
While an element awaits formal naming, it receives a systematic placeholder based on its atomic number using Latin and Greek numerical roots. Element 118, for example, was temporarily called “ununoctium” (un-un-oct-ium, or 1-1-8-ium). Element 113 was “ununtrium.” These placeholder names always end in -ium regardless of the element’s group, because they are not real names and do not need to follow the group-specific suffix rules. They exist purely so that scientists have something to call the element in papers and conference talks during the years between discovery and official naming.
The placeholder system was devised by IUPAC in the 1970s specifically to avoid the political disputes that had plagued element naming during the Cold War. For decades, American and Soviet laboratories both claimed priority for certain superheavy elements, and each side proposed its own name. Element 104, for example, was called “rutherfordium” in the West and “kurchatovium” in the Soviet Union. The temporary names took the politics out of day-to-day scientific communication. You could just say “unnilquadium” and everyone knew which element you meant, regardless of which national laboratory they supported.
Why It Matters That the Pattern Exists
The -ium ending might seem like a trivial piece of linguistic history, but it serves a real function. It instantly identifies a word as a chemical element. If someone mentions “livermorium” in conversation, you know without further context that it is an element, not a place or a person or a medical condition. This built-in labeling is surprisingly useful in technical communication, where ambiguity costs time and can cause real errors. “Germanium” is an element; “Germany” is a country. “Californium” is an element; “California” is a state. The suffix does the disambiguating work automatically.
The convention also makes chemistry slightly more learnable. Students encountering the periodic table for the first time can quickly see that the vast majority of entries follow a single naming pattern. The exceptions stand out and become memorable precisely because they break the rule. Asking “why doesn’t helium end in -on?” or “why is it called iron instead of ferrium?” turns out to be a productive way into the broader history of how humans have understood the elements. Those exceptions are not bugs in the system. They are windows into the centuries of guesswork, politics, and serendipity that built the periodic table into what it is today.
Non-English Periodic Tables
The -ium pattern is most visible in English, but it extends across most European languages because the Latin roots are shared. French, Spanish, German, Italian, and Portuguese all preserve -ium (or a local variant like -io in Spanish and Italian) for the same elements. Where things get interesting is in languages that do not derive from Latin. Mandarin Chinese, for instance, assigns a unique character to each element, with a radical (a sub-component of the character) indicating whether the element is a metal, a gas, or a liquid at room temperature. The -ium concept simply does not translate. Japanese uses katakana transliterations for many elements, preserving the sound of the international name, so “uranium” becomes ウラニウム (uraniumu). But older, well-known elements have native Japanese names entirely unrelated to Latin.
Arabic, Hindi, and Korean each have their own strategies for adapting or replacing the international names. The IUPAC rules govern the official international name in Roman script, but individual countries and language communities decide how to render that name in their own writing systems and pronunciation. The -ium suffix is therefore simultaneously universal, in the sense that IUPAC mandates it, and culture-specific, in the sense that billions of people learn the elements under entirely different naming conventions. What stays consistent across all of them is the underlying chemical identity. Whether you call element 26 iron, ferrum, hierro, Eisen, 铁, or 철, it still has 26 protons and behaves the same way in a reaction.