Quick Facts
| Property | Value |
|---|---|
| Symbol | O |
| Atomic Number | 8 |
| Atomic Mass | 15.999 u |
| Category | Nonmetal |
| Period | 2 |
| Group | 16 |
| Block | p |
| Electron Configuration | [He] 2s² 2p⁴ |
Physical Properties
| Property | Value |
|---|---|
| State at 20°C | Gas |
| Density | 0.001429 g/cm³ |
| Melting Point | -218.79°C (54.36 K) |
| Boiling Point | -182.95°C (90.20 K) |
| Appearance | Colorless gas (pale blue as liquid) |
Atomic Properties
| Property | Value |
|---|---|
| Electron Configuration | [He] 2s² 2p⁴ |
| Electronegativity | 3.44 (Pauling scale) |
| First Ionization Energy | 1313.9 kJ/mol |
| Atomic Radius | 60 pm |
| Covalent Radius | 66 pm |
| Van der Waals Radius | 152 pm |
History and Discovery
Discovered by: Carl Wilhelm Scheele and Joseph Priestley Year of Discovery: 1774 Location: Uppsala, Sweden and Wiltshire, England
Etymology
The name "oxygen" comes from the Greek words "oxy" (acid) and "genes" (forming), meaning "acid-former." Antoine Lavoisier named it in 1777, mistakenly believing all acids contained oxygen.
Discovery Story
Carl Wilhelm Scheele discovered oxygen around 1772 by heating various compounds, but his findings were not published until 1777. Joseph Priestley independently discovered it in 1774 by focusing sunlight on mercuric oxide and collecting the gas. Priestley called it "dephlogisticated air." Antoine Lavoisier later identified it as an element and gave it its current name.
Isotopes
| Isotope | Natural Abundance | Half-life | Decay Mode |
|---|---|---|---|
| ¹⁶O | 99.757% | Stable | - |
| ¹⁷O | 0.038% | Stable | - |
| ¹⁸O | 0.205% | Stable | - |
Occurrence
Natural Abundance
Oxygen is the third most abundant element in the universe and the most abundant element on Earth by mass (about 46% of Earth's crust). It makes up about 21% of the atmosphere and 89% of water by mass. It is found in countless minerals, oxides, and organic compounds.
Extraction and Production
- Fractional Distillation of Air: Primary industrial method
- Electrolysis of Water: Produces high-purity oxygen
- Pressure Swing Adsorption: For on-site oxygen generation
- Global production exceeds 100 million tons annually
Applications and Uses
Industrial Applications
- Steel production (basic oxygen process)
- Welding and cutting metals (oxy-acetylene torch)
- Chemical oxidation processes
- Waste water treatment
Medical Applications
- Oxygen therapy for respiratory conditions
- Anesthesia
- Hyperbaric oxygen treatment
- Life support systems
Aerospace Applications
- Rocket propellant oxidizer
- Life support in spacecraft and aircraft
- Altitude training for athletes
Other Uses
- Aquaculture (oxygenating water)
- Paper and pulp bleaching
- Glass manufacturing
- Enhanced oil recovery
Biological Role
Oxygen is essential for nearly all life forms. It is the terminal electron acceptor in aerobic respiration, allowing organisms to extract energy from food.
In the Human Body
- About 65% of body mass is oxygen (mostly in water)
- Essential for cellular respiration
- Carried by hemoglobin in red blood cells
- Required for metabolism of nutrients
Oxygen Cycle
Oxygen cycles between the atmosphere and living organisms through photosynthesis (producing O₂) and respiration (consuming O₂). It also interacts with the carbon and water cycles.
Importance for Life
Aerobic organisms require oxygen to produce ATP efficiently. Anaerobic organisms can survive without oxygen but produce less energy.
Safety and Hazards
Toxicity
Pure oxygen is not toxic at normal pressures for short periods, but prolonged exposure to high concentrations can cause oxygen toxicity, affecting the lungs and central nervous system.
Handling Precautions
- Powerful oxidizer—accelerates combustion
- Keep away from oil, grease, and flammable materials
- High-pressure cylinders require careful handling
- Oxygen-enriched atmospheres increase fire risk significantly
Environmental Impact
Ozone (O₃) in the stratosphere protects Earth from UV radiation, while ground-level ozone is a pollutant. Oxygen itself is environmentally benign.
Interesting Facts
- Oxygen is paramagnetic and is attracted to magnets
- Liquid oxygen is pale blue in color
- About 21% oxygen concentration is optimal for humans—too much or too little is harmful
- Oxygen was forming in the atmosphere about 2.4 billion years ago (Great Oxidation Event)
- An adult human inhales about 7-8 liters of air per minute