Introduction

The writing of this series of papers began in the Fall of 2022. From then to the writing of this study, there are still 118 known elements that are uniquely defined by their atomic number (Z), i.e., the number of protons in the nucleus. Almost every element has at least one or even several isotopes that are defined as species with the same number of protons but a different number of neutrons. The difference in the number of neutrons generally has little effect on the chemistry of a given element. In the case of hydrogen, however, it must be acknowledged that hydrogen isotopes with 0, 1 and 2 neutrons respectively are sometimes referred to as protium, deuterium and tritium, and all three can be considered different elements. Exotic hydrogen-like species also include positronium, muonium and muonic helium, which can also be considered isotopes of hydrogen. Some of these names, as with the other more "classical" elements, are sensibly protium, deuterium and tritium. They refer to primary (one), second (two) and third (three) forms of elemental hydrogen. Many, indeed most, element names are not sensible.

Enormously higher than the number of elements or their isotopes is the number of chemical species, which is well over 108 known chemical species, and much more if DNA and protein sequences and fragments are included. In contrast, there are calorimetrically derived thermochemical data for not much more than 104 and certainly less than 105 species. The extremely demanding requirement for careful measurements on high-purity samples has meant that there are very few laboratories today whose goal and activity is to measure and understand these quantities. In this context, one of the most important research activities of the authors has been the understanding, but never the measurement, of the quantities that arise from these studies.

In the case of many chemical substances, it should be noted that their name or the name of their species can easily lead to a misconception of the actual composition or structure of a compound. In the chemical community; however, trivial and completely unsystematic names are preferred to the complicated systematic names. Often there is a certain similarity of names, but in most cases the only common feature is that these compounds are "chemicals." They often do not even have the same origin, e.g., "inorganic" as opposed to "organic".

In our recent multi-part study, we reported on selected examples of compounds/species with a subjective phonetic sound similarity for each element of the periodic table. In the first part [1, 2], we discussed the elements from hydrogen (H) to argon (Ar) (Z = 1 to 18). In the second part [3], we discussed the elements from potassium (K) to xenon (Xe) (Z = 19 to 54). In the third part [4], we discussed cesium (Cs) to radon (Rn) (Z = 55 to 86) and in the fourth part we discussed francium (Fr) to oganesson (Og) (Z = 87 to 118) [5]. In the present study in Structural Chemistry, we continue our efforts to find a compound with a subjective phonetic sound similarity for selected isotopes of the periodic table. We thus consider this paper as part 5 of our study having earlier planned only four parts. In this part we have instead of one category of compounds only, two major distinct categories: one of similar sounds as done before and one “playing” with numbers, e.g., C-12, 12 carbons; F-19, 19 fluorines.

At this point we also acknowledge that our interest is in etymology and that word origins for unsystematic and trivial names are not the aim of this study and would be an excessive diversion of our activity. This is so also because in many cases, the origin of trivial names is difficult to find and in some other cases we do not even know how to find it. Many of the compounds are rather “exotic” and from the conceptual point of view their names also far less important than the elements gathered in a periodic system masterpiece, for which chemist Peter Atkins wrote “The periodic table is arguably the most important concept in chemistry [6]”. Year 2019 has been even designated by UNESCO as the International Year of the Periodic Table. A lengthy and thorough multipart recent literature study on the origin of the names of the elements [7,8,9] was also published recently, and while we laud this study, we do not wish to emulate it for the names of the compounds (also for the above given reasons). Furthermore, although there may be alternative choices of compounds with appropriate names and some even with the desired calorimetric measurements, we have avoided such compounds of interest to pharmaceutical and agricultural chemistry because we are reluctant to "advertise" one company over another.

This study reflects our long-term interest in chemical energetics, etymology, and wordplay. The compounds in the current study were selected based on the similarity of the sound (and/or scientific origin) of the element name. These compounds for which a key energetics quantity (most generally the enthalpy of formation) is known from experiments served as the study subjects. In no case do we present a compound because that species "only" contains that element. In most cases primary sources were used as reference sources for thermochemical data; however, in some cases secondary sources, i.e., the "Domalski compendium" [10], the “Wagman et al. compendium” [11] or the “Pedley compendium” [12] were also used. The "missing" data are admittedly quite old and we are surprised that they are missing from these sources. We wish to encourage the remeasurement of these enthalpies of formation (Table 1).

Table 1 Isotopes of hydrogen, namely protium, deuterium, tritium, positronium, muonium and muonic helium; some selected isotopes of other atoms (C, F, U)
Full size table

Conclusions

Similar phonetic of semi-systematic or trivial names of the names are similar to those of the elements but the differences in expected and actual composition surprises. Due to their simplicity, semi-systematic or trivial names remain preferred by the chemical community.