Allotropies

Part of speech: noun

Definitions

1. The various structural forms in which a substance can exist, such as carbon in diamond and graphite
2. Different configurations of an element that display distinct physical properties, like oxygen as O2 and ozone as O3
3. The phenomenon by which a single element can take on multiple forms, each with unique characteristics and behaviors in its natural state

Etymology: Allotropies are the different structural forms an element can take, and the word traces back to a deliberate coinage by the Swedish chemist Jöns Jacob Berzelius. He built it from Greek roots: "allo" meaning "other" and "tropos" meaning "turn" or "way," so the term describes an element that turns up in another form. Berzelius applied it to phenomena such as oxygen and ozone, which are both made purely of oxygen atoms yet behave quite differently. The Greek form "állotrophia" was itself assembled from the same building blocks, which is why the word feels classical even though no ancient Greek writer ever used it in a chemical sense. The plural simply counts the number of such forms, as in carbon's well-known allotropies of graphite, diamond and fullerenes.