A chemical by any other name would smell as sweet

Recently, I’ve noticed that I use a plethora of chemical words without even thinking about them. My parents gently remind me of this when they ask me what I’m researching or reading and have to tell me every five minutes to ‘speak in English, not in chemistry’. It’s true that chemistry has its own language, with many people having noted the resemblance of chemistry to the pictorial nature of Mandarin, with curly arrows, mechanisms and balanced equations. But where do the chemical words that we use come from?

The lexicographer Susie Dent inspired me to start investigating. A favourite pastime of mine is tuning in to the word-based TV game show Countdown, first introduced to me by my parents as a way of keeping the old grey matter fresh during the Covid-19 lockdown. Today, I am still an avid player, albeit increasingly for Dent’s segment ‘Origin of Words’, where she discusses the etymology of common words. In that spirit, let’s do our own digging and look at some chemistry terms.

As a young chemistry student, I was taught to use the Cahn-Ingold-Prelog (CIP) rules to describe the isomers of alkenes. The highest priority group on each carbon atom can be on opposite sides of the double bond (E), or on the same side (Z). This intrigued me. Why is it not the other way around when the shape between two opposing groups neatly forms a Z shape?

I later discovered that E and Z come from the German entgegen (apart) and zusammen (together). The choice for German here was likely influenced by Vladimir Prelog, who was based in German-speaking Zurich at the time of developing the rules. I was reminded of this origin when seeing a climate strike poster in Berlin stating in bold letters: ‘together for the climate’ (zusammen für das Klima).

Cross purposes

Alkenes with functional groups on opposite sides of the double bond can also be thought of as trans, stemming from the Latin transire, meaning to cross; those with functional groups ‘on the same side as’ one another are conversely known as cis isomers.

The CIP rules also extend to how we talk about stereocenters, particularly those of carbon. Like geometric isomerism in alkenes, there’s been an evolution in the way we describe stereocenters, a fact highlighted to me in lectures by the differing ways in which biologists and chemists discuss chirality.

Chirality itself comes from the Greek kheir, meaning hand

Chirality is nearly always illustrated to students by getting us to look at our hands and recognise that they are non-superimposable mirror images of each other. It is no surprise then to learn that chirality itself comes from the Greek kheir, meaning hand. When plane polarised light is shone at a chiral compound, the light is deflected to either the left or right. This phenomenon is captured in the way that we describe such molecules. Originally, the d/l system was used, with d coming from dexter, Latin for ‘to the right side’, and l from laevus, ‘to the left side’; this nomenclature is still used, predominantly in biological contexts.

Nowadays, chemists tend to use the CIP convention of R/S. R takes itself from the Latin rectus, meaning correct or straight, whereas S comes from the Latin sinister, meaning ‘on the left (hand)’. (Perhaps this also explains why those that are left-handed were once seen as evil.) The differing ways of discussing stereocenters is a matter of preference, yet it is intriguing to see that both stem from Latin.

For any student, these rules are largely arbitrary. However, by delving into their origins, we can learn about their history, as well as finding handy ways of remembering them!

Breaking convention

There are more stories to be found in the rest of the periodic table. Why, for example, do a large proportion of elements end in -ium? When elements were being discovered in the 19th and 20th centuries, the predominant academic language was Latin. The suffix -ium was added to the ending of the Latin words for the sources in which these metals were found, such as calx for calcium. It is now Iupac convention to name most new (usually metallic) elements with this suffix.

Other conventions include using the -on suffix for noble gases. But hang on – why then, does helium differ? The Greek helios, for sun, was used to name helium, after it was first detected in the sun in 1868. Upon analysis, it was thought that the spectral lines aligned with those an alkali metal, and hence given the usual -ium ending. Once it was realised that helium was in fact a noble gas, its name had already stuck. Perhaps, instead, we should rename it helion!

You don’t have to know Latin or Greek or German to understand chemistry. However, if we scratch the surface of our everyday chemical terms, we might just uncover something interesting, learn a little history and even have some fun.