Marie Anne Paulze no descubrimento do osíxeno

Nunha comunicación presentada por nós no XXXII Congreso de ENCIGA, celebrado en Viveiro no ano 2019, titulada “MARIE ANNE e a TÁBOA PERIÓDICA” falabamos da vida desta científica para, comprendendo como fora a súa formación académico-científica, estar en condicións de asimilar mellor as súas contribucións ao desenvolvemento da Táboa Periódica, na celebración do “ Ano Internacional da Táboa Periódica”. Tamén pretendiamos comprender cal foi a contribución de Marie ao mundo da química axudando ao seu gran Pygmalion: Antoine Laurent Lavoisier. Nesa comunicación pódese entender cal é a nosa reflexión sobre a súa contribución ao desenvolvemento da táboa periódica ao longo do último terzo do século XVIII, de modo particular; canto debeu colaborar Marie Anne – sempre do lado e da man do seu admirado e idolatrado Lavoisier- ao establecemento da primeira táboa das “Substancias simples” que aparece no “Tratado Elemental de Química” publicado por Antoine no ano 1789. Debemos lembrar que a táboa periódica que hoxe coñecemos e celebramos é froito do xenio de Mendeleev; pero tamén debemos citar a importancia das contribucións de Julius Lothar Meyer (quen fai 150 anos chegou ás mesmas conclusións que Dimitri, pero non se atreveu a publicalas e, por iso, chegou tarde á historia).Tamén cómpre insistir en que houbo moitas outras achegas na historia da química á construción da táboa periódica definitiva. Hai algunha evidencia da posible contribución de Marie Anne á construción ou elaboración das distintas táboas periódicas da historia? Estivo presente ou actuou significativamente no descubrimento dalgún elemento químico? Verémolo logo.

Editorial

Dear reader, This year is full of events, anniversaries and milestones. Not only does HTHP celebrate its 50th anniversary, but also the Periodic Table of Elements has its 150th birthday. In 1869 Dimitri Mendeleyev and Lothar Meyer discovered and presented this table. In order to commemorate this breakthrough, UNESCO has declared 2019 as the “International Year of the Periodic Table of Chemical Elements”. In addition, another important event takes place in May 2019. The Conférence Générale des Poids et Mesures will put into effect the new SI system of units on May 20, 2019, the “World Metrology Day”. The introduction of this new system marks a change in paradigm: the new system relates all units to fundamental constants, rather than artefacts. The most prominent example is the definition of the new kilogram, which is now linked to the Planck constant, h. Of course, all of this has an impact on thermophysical property measurements. Therefore, we have asked Dr. Matthieu Thomas from the Laboratoire National de Métrologie et d’Essais (LNE), France, to explain shortly how this new definition works and how it was implemented. Dr. Thomas is involved in the Kibble balance project of LNE, a key element in the realisation of the new kilogram. You find his article in this issue of HTHP. The editors thank Dr. Thomas for his cooperation; we hope you will enjoy reading his article as well as the rest of this issue.

The Electron and Chemical Periodicity

J.J. Thomson’s discovery of the electron is one of the most celebrated events in the history of physics. What is not so well known is that Thomson had a deep interest in chemistry, which, among other things, motivated him to put forward the first explanation for the periodic table of elements in terms of electrons. Today, it is still generally believed that the electron holds the key to explaining the existence of the periodic table and the form it takes. This explanation has undergone a number of subtle changes. The extent to which the modern explanation is purely deductive or whether it is semiempirical is examined in this chapter. While Dmitri Mendeleev had remained strongly opposed to any attempts to reduce, or explain, the periodic table in terms of atomic structure, Julius Lothar Meyer was not so averse to reduction of the periodic system. The latter strongly believed in the existence of primary matter and also supported William Prout’s hypothesis. Lothar Meyer did not hesitate to draw curves through the numerical properties of atoms, whereas Mendeleev believed this to be a mistake, since it conflicted with his own belief in the individuality of the elements. This is how matters stood before the discovery of the electron, three years prior to the turn of the twentieth century. The atom’s existence was still very much a matter of dispute, and its substructure had not yet been discovered. There appeared to be no way of explaining the periodic system theoretically. Johnston Stoney first proposed the existence and name for the electron in 1891, although he did not believe that it existed as a free particle. Several researchers discovered the physical electron, including Emil Wiechert in Königsberg, who was the first to publish his findings. Because these early researchers did not seriously follow up on their results, it was left to the British physicist Thomson to capitalize upon and establish the initial observations.

Discoverers of the Periodic System

The periodic system was not discovered by Dmitri Mendeleev alone, as is commonly thought, or even just by Mendeleev and Julius Lothar Meyer. It was discovered by as many as five or six individuals at about the same time, in the decade of the 1860s, following the rationalization of atomic weights at the Karlsruhe conference. It became apparent by the middle of the nineteenth century that something needed to be done to resolve the widespread confusion over equivalent and atomic weights. Amedeo Avogadro had already proposed a solution to Gay-Lussac’s law that preserved John Dalton’s indivisible elemental particles. Recall that Gay-Lussac had observed that volumes of gases entering into chemical combination and their gaseous products are in a ratio of small integers. Dalton had refused to accept this viewpoint because it implied that atoms appeared to divide in some instances, such as the combination of hydrogen and oxygen to create steam. Avogadro had suggested that such “atoms” must be diatomic; that is, in their most elemental form they must be double. Thus, the oxygen atom was not dividing; rather, it was an oxygen molecule, which consisted of two oxygen atoms, that was coming apart. Unfortunately, the terms in which Avogadro expressed his views were rather obscure and failed to make much impression on the chemists of the day. Two exceptions were the French physicist and chemist André Ampère and the Alsatian chemist Charles Gerhardt, both of whom adopted the view that elemental gases were composed of diatomic molecules. One consequence of the general refusal to recognize the existence of diatomic molecules as the ultimate “atoms” of gaseous elements was that, as mentioned in chapter 2, the confusion between equivalent weights and atomic weights continued to reign. Although the relative weights of oxygen to hydrogen in water are approximately 8 to 1, the relative weight of the oxygen atom to the hydrogen atom takes on values of 8 or 16 depending on what one considers the correct formula for water to be.