In 2019, the 150th anniversary of the Periodic Table of chemical elements is celebrated. Within the scope of this ephemeris, I will write, throughout this year, several chronicles about some chemical elements. Today is the day to start with oxygen (chemical symbol O).
Oxygen was identified as a chemical element in 1774 by Joseph Priestley (1733-1804), one of those responsible for the foundations of modern chemistry during the XNUMXth century.
English by birth, Priestley was, in addition to being a chemist, also a nonconformist cleric and a controversial personality who intellectually marked his time, having apparently exerted great influence in the drafting of the text of the Declaration of Independence of the American Colonies (which would later give rise to to the United States of North America) and was a personal friend of Benjamin Franklin.
To identify oxygen, Priestley used two glass lenses to focus sunlight onto a vial containing mercury oxide. This compound, thus heated by the solar star, “released” bubbles of a “life-generating gas”.
The attribution of the discovery of molecular oxygen to Priestley is due, fundamentally, to the fact that he was the first to understand being in the presence of a substance that was part, among others, of the air we breathe. It is also attributed to the identification of nine other different gases, of which only three were, until then, known.
The identification of oxygen – or “dephlogisticated air”, as it was initially called by Priestley, taking into account the dogmatic theory of the time – was very important in the history of the development of chemistry, as it allowed, among other things, to understand (as if said) that air was not, in itself, a single element, but composed of several substances.
The Greeks considered the air as a unique element and this conception was dominant for millennia. However, there is some evidence that the Chinese already knew, in the 1452th century, that air did not have a “simple nature”. Interestingly, the genius of Leonardo da Vinci (1519-XNUMX) would have identified, first, that “a part” of air had an “important role” in combustion.
As is often the case in science, others before Priestley would have already “stumbled” on oxygen (in addition to having always breathed it!).
However, because they interpreted their results differently, or because they did not disclose the discovery in time, they did not take the credit for the discovery. This was the case with the Swedish chemist Carl W. Scheele (1742-1786), who is now known to have obtained pure oxygen from nitrates and by other methods, between 1771 and 1773. However, Scheele only released his discovery in 1777, that is, three years after Priestley.
The understanding of the true nature of oxygen is due, however, to the great French chemist Antoine Lavoisier (1743-1794), who, based on the works of Priestley and Scheele, characterized this element in a quantitative way. Lavoisier is often referred to as “the father of modern chemistry”, as he was the first to base his conclusions on the results of his experiments in a quantitative way.
Despite his genius, it is due to Lavoisier the improper baptism of this element by “oxygen”. Based exclusively on his experimental observations, he found that some elements, when combined through combustion with oxygen, generated compounds that “behaved” like acids.
So Lavoisier generalized that oxygen was a fundamental constituent of all acids, which we know to be incorrect. For example, hydrochloric acid (which is a strong acid) does not have oxygen in its composition.
Based on this fatal generalization, Lavoisier used the Greek words “oksys” and “gen” – which mean, respectively, “acid” and generator” – to construct the word oxygen (acid generator) and it is by this name that we designate this element since then.
I leave, for now, the challenge to the reader to find the location of oxygen in the Periodic Table! I help you by saying that 8 is the atomic number of oxygen.
In the next chronicle, I'll give this subject more oxygen!
Author Antonio Piedade
Science in the Regional Press – Ciência Viva
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