Oxygen (O)
“Breathe in: one in every five air molecules just entered you — the restless element that turns food into energy, iron into rust and sparks into flame.”
How its electrons are arranged
Computed from the aufbau principle, with known real-world exceptions applied automatically.
Characteristics
- The great joiner: oxygen combines with nearly every element — metals tarnish, iron rusts, wood burns — usually paying out energy as oxides form.
- It feeds combustion without being a fuel itself: a glowing splint bursts back into flame in pure oxygen, the classic laboratory test for the gas — yet a jar of oxygen alone never catches fire.
- Configuration 1s² 2s² 2p⁴: two electrons short of a full outer shell, so an oxygen atom hungrily gains or shares two electrons, becoming the oxide ion O²⁻ or a pair of covalent bonds.
- About 65% of a human body’s mass is oxygen — mostly as water — making it the most abundant element in the body; green plants refills the sky’s supply day after day through photosynthesis.
A colourless, odourless gas that makes up about 21% of the air, normally travelling as O₂ molecules — two atoms locked in a double bond. Slightly denser than air, it dissolves in water just enough for fish to breathe. Cooled to −183 °C it becomes a striking pale-blue liquid; even the gas itself is faintly, sky-pale blue.
Where you meet it
✦ Uses
- Medical oxygen: the cylinders and pipelines of every hospital ward — pneumonia and COVID-19 patients breathe life from them, and welding shops across Bangladesh run on the same compressed cylinders.
- Oxy-acetylene and oxy-LPG torches: flames around 3,500 °C, hot enough to slice through steel plate in shipyards, workshops and roadside repair sheds.
- Steelmaking: the basic oxygen furnace blasts pure oxygen through molten pig iron and burns off its carbon in minutes — the route by which most of the world’s steel is born.
- Rocketry and life support: liquid oxygen is the oxidizer that burns rocket kerosene, and spacecraft crews carry tanks of oxygen, not of air.
◍ Everyday examples
- Every breath you take: oxygen crosses from lung to blood, and inside your cells it quietly “burns” food to release the energy that keeps you alive.
- The rust blooming on iron railings and tin roofs after Bangladesh’s monsoon rains is iron yielding to oxygen and moisture.
- Fish breathe through gills — the oxygen dissolved in pond and river water is their lifeline, which is why a fish suffocates in a polluted pond.
History & name
Oxygen was discovered twice over. The Swedish apothecary Carl Wilhelm Scheele made it first, around 1771–72, by heating several compounds — but his publisher shelved the account until 1777. Meanwhile, in 1774, Joseph Priestley in England focused sunlight through a lens onto mercuric oxide and collected a gas in which a candle “burned with a amazingly vigorous flame”. Neither man grasped what he held: both were committed phlogiston theorists. It took Antoine Lavoisier’s painstaking weighing to prove that this “dephlogisticated air” was a true element and the real partner of combustion — and he named it oxygen, “acid-former”, in the honest but mistaken belief that every acid contained it.