II · THE DISCOVERY · HISTORY OF SCIENCE
Oxygen
The gas that makes up a fifth of the air around you was pulled out of that air twice before anyone understood it was an element at all.
At a glance
- Discovered
- 1771 in Sweden; 1774 in Calne, England
- Credited to
- Carl Wilhelm Scheele and Joseph Priestley (contested)
- Symbol
- O
- Atomic number
- 8
Look closer
Two dates, two places
The discovery is recorded as happening twice: in 1771 in Sweden, and in 1774 in Calne, a town in England. That double entry reflects a genuine ambiguity. Carl Wilhelm Scheele isolated the gas in Sweden, and Joseph Priestley isolated it independently in Calne. The facts mark the discovery as contested, meaning credit is shared between them rather than settled on one.
Named after acid
The name oxygen comes from the word for acid. That etymology reflects an early misunderstanding: the chemist who named it believed the element was a necessary component of all acids, which turned out not to be true. The name stuck anyway, even after the theory behind it was discarded.
A chalcogen and a lithophile
Oxygen is classed as a chalcogen, a member of group 16 in the periodic table, which also includes sulfur and selenium. It is also termed a lithophile element, meaning it tends to concentrate in rocky material rather than in metal or sulfide ores. Both classifications describe where oxygen sits in the broader scheme of elements and where it is found in the Earth.
The story
Oxygen is a chemical element with the symbol O and atomic number 8. It belongs to the chalcogen group in the periodic table. At ordinary temperature and pressure, two oxygen atoms bind together to form dioxygen, a colourless and odourless gas with the formula O2. This is the form that makes up roughly a fifth of the air in the Earth's atmosphere.
The element was isolated independently by two men working in different countries. Carl Wilhelm Scheele isolated it in Sweden, with the discovery dated to 1771. Joseph Priestley isolated it in Calne, in England, with the discovery dated to 1774. The record marks the discovery as contested, reflecting the fact that credit is shared between them. Priestley called the gas dephlogisticated air and did not recognise it as a chemical element. It was Antoine Lavoisier who named it oxygen and characterised its role in combustion, work he published in 1777.
The name oxygen derives from the word for acid. Lavoisier believed the element was a necessary part of all acids, which later turned out to be incorrect, but the name remained.
Oxygen is highly reactive. It forms compounds called oxides with most other elements, often releasing energy in the process. Combustion, the burning of fuel in air, is a reaction between the fuel and oxygen. Rusting is another oxide-forming reaction, slower but following the same principle: iron combines with oxygen to form iron oxide.
In living organisms, oxygen plays a central role in cellular respiration, a process that extracts energy from food. The organism takes in oxygen, reacts it with organic molecules derived from what it has eaten, and releases carbon dioxide as waste. Most complex life depends on this process.
Oxygen in the atmosphere is replenished by photosynthesis. Plants, algae, and certain bacteria use energy from sunlight to split water molecules, releasing oxygen as a byproduct. Without this continuous production, the reactive oxygen in the air would combine with other substances and disappear.
A rarer form of oxygen, ozone, has the formula O3. It forms a layer in the lower stratosphere that absorbs ultraviolet radiation, shielding life on the surface from damage. At ground level, however, ozone is a pollutant formed in smog.
Why it mattered then
Before oxygen was isolated and understood, combustion and respiration were explained through a theory called phlogiston, which held that burning substances released an invisible substance into the air. The discovery and naming of oxygen overturned that model. Once Lavoisier characterised oxygen's role in combustion, chemists could describe burning and breathing as reactions between substances and a specific gas, rather than as the release of an imagined essence. That shift laid the groundwork for modern chemistry, replacing a theory that could not be tested with observations of measurable substances combining in predictable ways.
Why it matters now
Oxygen is used in steel production, where it is blown through molten iron to burn off impurities. It is used in welding and cutting metals, in rocket propellant, and in medical oxygen therapy for patients whose lungs cannot take in enough from the air. Life-support systems in aircraft, submarines, spacecraft, and diving equipment carry supplies of it because the human body cannot function without a continuous supply. The element also remains central to how we understand energy in living systems: the respiration that powers cells, and the photosynthesis that replenishes the oxygen those cells consume, are both described in terms of oxygen moving between molecules.
The surprising detail
The element was isolated by Michael Sendivogius before 1604, more than a century and a half before the dates usually given for its discovery. That earlier work did not lead to recognition of oxygen as an element, and the discovery is credited to Scheele and Priestley instead. The gap between isolating a substance and understanding what it is can be longer than the gap between one discovery and the next.
What is disputed
The discovery is recorded with two dates, 1771 and 1774, and two locations, Sweden and Calne. The facts mark it as contested, meaning credit is shared between Carl Wilhelm Scheele and Joseph Priestley rather than settled on one. The reference text mentions an even earlier isolation by Michael Sendivogius before 1604, but that isolation is not reflected in the verified discovery dates, and the lesson follows the dates the facts give.
Remember this
Two chemists isolated oxygen independently in the 1770s, but neither recognised it as an element. A third man named it and explained what it did.
Test yourself
Why is the discovery of oxygen recorded as contested, with credit given to two people?
Carl Wilhelm Scheele isolated oxygen in Sweden in 1771, and Joseph Priestley isolated it independently in Calne, England, in 1774. Both men produced the same gas, but neither recognised it as a chemical element. The discovery is marked as contested because both isolations are documented, and there is no single agreed priority between them. Priestley called it dephlogisticated air; it was Antoine Lavoisier, working later, who named it oxygen and explained its role in combustion. The contested credit reflects the fact that isolating a substance and understanding what it is are two different achievements.