SUMMARY: HISTORY OF ATOMIC WEIGHTS
ARTICLE: ATOMIC WEIGHTS
AUTHORS: JOAQUÍN RODRÍGUEZ AND DAVID RODRÍGUEZ
YORLENIS MARIA NÚÑEZ ÁLVAREZ DANNA PAOLA RUÍZ PÁEZ
UNIVERSIDAD DE CÓRDOBA FACULTAD DE CIENCIAS BÁSICAS
PROGRAMA DE QUÍMICA INGLES
MONTERÍA-CÓRDOBA 2021
HISTORY OF ATOMIC WEIGHTS
From the beginning of chemistry, the concept of atomic weights was fundamental, since it is a differential magnitude of each of the atoms of the different chemical elements. Atomic weights are a dimensionless physical quantity, defined as the ratio of the average mass of an element's atoms (from a given sample or source) to one- twelfth of the mass of a carbon-12 atom (known as a unified atomic mass unit). The concept is generally used without qualification to refer to the standard atomic weight, which is published at regular intervals by the IUPAC Commission on Isotope Abundance and Atomic Weights. They are intended to be applicable to normal laboratory materials. In order to arrive at the conception of what today we know as atomic weights, historically a series of procedures that were clearly important for its development occurred, many scientists made great contributions with their discoveries, thus reaching the elaboration, ordering and periodic classification.
Among the first generations of chemical atomists who began with the contribution in the concept of atomic weight are named John Dalton and John Jacob Berzelius. But before talking about his great contributions, it is essential to appoint the French chemist, biologist and economist Antoine-Laurent Lavoisier who, with his work during the seventies and eighties of the eighteenth century, decided to take weight as the main and central measure of the amount of matter.
These works together with those of the French Claude Louis Bertthollete (1743- 1794) and the German Hieronymus Theodor Richter (1824-1898) had a direct impact on the Proust hypothesis (Law of Defined Proportions) attributed to Joseph Proust in 1799, where he exposes the analysis of various samples of copper carbonate and some natural minerals, purifying them and thereby demonstrating that they all had the same composition. which allows John Dalton to make the first table of atomic
weights from these hypotheses. Atomic weights were originally defined in relation to the element hydrogen, the lightest, arbitrarily taking it as 1. As well as Dalton, there are also scientists like Humphry Davy and William Prout who took this same value.
However, Berzelius soon proved that this hypothesis did not always hold up in some cases. It is also important to mention that, in the analytical development, I determined that oxygen represented 88.8%, which meant that if H = 1 CU, then O ≈ 16 CU. Which led to a major feud with Dalton. Although finally Berzelius drew up a table of atomic weights based on a new reference atomic mass unit. But later Berzelius in an exchange of data and discussions with other scientists such as Justus von Liebig, Jean-Baptiste-André Dumas, Charles Marignac, among others, during the period from 1838 to 1849
about the weights of fundamental elements such as hydrogen., oxygen and carbon, where it was concluded that Berzelius' experimental data for carbon was wrong since it was a weight of the order of 2% higher than it should be. Later works by Jean Servais Stas where he used O = 16 as a standard, showed that the atomic weights were not natural numbers, which indicated the end of the Prout hypothesis.
Finally, it is important to note the contributions of the scientists of Edward Morley and, above all, Theodore W. Richards, who, thanks to his determinations on the atomic weight, was the one who established the atomic weight of 55 elements, in addition, he was the first to find indications of the existence of isotopes by chemical methods when comparing samples of mineral lead and lead obtained by nuclear decay. After the development of the mass spectrometer, atomic weights could already be established more easily and above all with more precision. Finally, a review of many determinations in atomic theory is carried out, such as the chosen atomic mass unit, the problem of the chemical and physical scales of atomic weights, and the choice of 12C by the IUPAC, for the definitive statement of what we know today as the table of atomic weights.
