Early Observations:
* Ancient Greeks: Philosophers like Empedocles and Aristotle recognized that air was a mixture, but they didn't identify oxygen as a distinct component.
* 17th Century: Robert Boyle conducted experiments showing that air was essential for combustion, but he didn't identify oxygen as the responsible component.
The Key Experiments:
* Carl Wilhelm Scheele (1772): He isolated a gas that supported combustion better than air. He called it "fire air" because it was crucial for burning. Unfortunately, he didn't publish his findings immediately.
* Joseph Priestley (1774): Independently of Scheele, Priestley heated mercury oxide and collected a gas that allowed a candle to burn more brightly. He called it "dephlogisticated air" based on the prevailing phlogiston theory (a theory that explained combustion as the release of a substance called "phlogiston").
Naming and Characterization:
* Antoine Lavoisier (1770s): While he didn't discover oxygen himself, Lavoisier conducted extensive experiments on combustion and respiration. He disproved the phlogiston theory and correctly identified oxygen as a component of air, essential for both combustion and respiration. He named it "oxygen" based on its role in the formation of acids (from the Greek words "oxys" meaning "acid" and "gennao" meaning "to generate").
* John Dalton (1808): His atomic theory helped to solidify the understanding of oxygen as a distinct element with its own specific atomic weight.
So, how did they know it was a new element?
* New properties: Oxygen had properties distinct from other known gases like nitrogen, carbon dioxide, and hydrogen. It supported combustion, was crucial for respiration, and had a distinct chemical reactivity.
* Careful experimentation: Through rigorous experimentation, scientists were able to isolate oxygen, study its properties, and distinguish it from other known substances.
* Disproving existing theories: The discovery of oxygen helped to overturn the phlogiston theory, which had been the dominant explanation for combustion for over a century. This highlighted the need for new explanations and the importance of experimental evidence.
The discovery of oxygen was a landmark achievement in chemistry, paving the way for further advancements in understanding the composition of matter and the nature of chemical reactions.
