How Many Chemical Elements are there in the Universe? A (not so) Bohring Question

Abstract This paper replies to two of the most common questions that students usually pose to their teacher during a general chemistry course, i.e. how many chemical elements are in the Periodic Table and how many could be in our Universe. Reply to the former question can be easily found either in the literature or in any updated chemistry book. More interestingly, this communication shows that the latter question may be (simply) answered by making reference to the Bohr's atomic model that, notwithstanding its well-known limits, allows teachers to demonstrate that (for a hydrogenoid atom) 137 is the highest possible value for Z, as predicted by quantum electrodynamics, a much more complicated theory, usually taught in Physics advanced courses

Thermodynamics of hydrogen adsorption on calcium exchanged faujasite-typezeolites

A combination of variable-temperature infrared spectroscopy with volumetric gas adsorption measurements was used to study the thermodynamics of hydrogen adsorption, at a low temperature, on calcium-exchanged zeolites X and Y. Two adsorption regimes were considered: (i) localized adsorption of dihydrogen molecules on Ca2+ cation sites, and (ii) delocalized hydrogen adsorption following saturation of the Ca2+ adsorbing centres. For localized adsorption, the corresponding enthalpy change was found to be in the range of −12 to −15 kJ mol−1, while the isosteric heat of delocalized adsorption was found to be in the range of 4.5–5.5 kJ mol−1. These experimental results are discussed in the broader context of corresponding data for other alkaline zeolites, with a focus on correlation between adsorption enthalpy and entropy for the localized adsorption regime.Financial support from Regione Piemonte (CIPE Project C72), MUR (2004 FISR Project “Vettore Idrogeno”), Spanish MEC and FEDER funds (Project MAT2005- 05350) and from the Conselleria d’Economia, Hisenda e Innovació de les Illes Balears (Project PROGECIB-22A) is gratefully acknowledged.Peer reviewe