Oxygen is the eighth element of the periodic table. It is atomic number 8 with element symbol O. Oxygen is best known as the element we need in order to breathe, but it has many other interesting properties. These oxygen facts contain chemical and physical data along with general information and history.
Basic Oxygen Facts
Name: Oxygen
Atomic Number: 8
Element Symbol: O
Group: 16
Period: 2
Block: p
Element Family: nonmetal
Atomic Mass: [15.999 03; 15.999 77] IUPAC guidelines. For single value, use 15.9994.
Electron Configuration: [He]2s22p4 (shorthand) or 1s22s22p4 (full)
Discovery, Naming,, and Isolation
Discovery
Most sources attribute the discovery of oxygen to either Carl Wilhelm Scheele in 1773 or Joseph Priestley in 1774. Priestley is often given priority because his work was published first. Both men noticed heating particular oxides released a gas which caused candles to burn brighter. Priestley went a bit further by placing a mouse in a jar of oxygen. He expected it to survive only a few minutes before suffocating. Instead, the mouse was still alive after an hour in the jar.
- Scheele (1772) first produced oxygen by heating compounds like mercuric oxide and potassium nitrate but did not publish his findings until 1773.
- Priestley (1774) independently discovered the gas by focusing sunlight on mercuric oxide and collecting the resulting gas. He described it as “dephlogisticated air.”
- Lavoisier (1777), often credited with naming the element, demonstrated that oxygen was a component of air and essential for combustion, effectively disproving the phlogiston theory.
Michael Sendivogius and Early Ideas
There is some debate among historians about whether Michael Sendivogius (Michał Sędziwój), a 16th-century Polish alchemist, deserves credit for discovering oxygen. Sendivogius described a “vital spirit” in the air, which he believed was essential for life. While his observations were insightful, modern scholars generally agree that he did not isolate or identify oxygen as an element. Instead, his work laid early groundwork for understanding air’s role in combustion and respiration.
Naming
French chemist Antoine Lavoisier named the element oxygene from the Greek words oxys meaning “acid” and genes meaning “forming”. At the time, it was believed all acids required oxygen to part of the reaction.
Isolation
Isolation of pure oxygen occurs through techniques like fractional distillation of liquefied air and electrolysis of water.
Appearance and Allotropes
Oxygen exists in multiple forms and states, each with unique characteristics.
Appearance: Oxygen is colorless, odorless, and tasteless in its gaseous form. As a liquid or solid, it exhibits a pale blue color.
Oxygen gas (O₂): The most stable and common form.
Solid oxygen: Exists in several crystalline forms, including a metallic phase under extreme pressures.
Ozone (O₃): A triatomic allotrope with a sharp odor, found in the stratosphere, where it protects life from ultraviolet radiation.
Tetraoxygen (O₄): An ephemeral species found under high-pressure conditions.
Element Group
Oxygen is part of the chalcogen group (Group 16) in the periodic table. It shares common properties with other members of this group, such as sulfur and selenium. There three elements are nonmetals with comparable chemical properties.
Oxidation States
Oxygen exhibits various oxidation states, enabling its versatility in chemical reactions. This section focuses on the most common states and their chemical relevance.
Oxygen exhibits oxidation states ranging from −2 (most common) to +2 in rare compounds. The primary states are −2 in oxides and −1 in peroxides.
Isotopes
Natural oxygen consists of three stable isotopes: 16O, 17O and 18O. 16O accounts for 99.762% of the natural abundance. Radioactive isotopes range in atomic mass from 12O to 24O. Oxygen-15 is notable for its use in medical imaging (PET scans).
Characteristics and Key Properties
Oxygen’s unique chemical and physical properties make it indispensable to science and technology.
Chemical Properties: Oxygen readily forms oxides, peroxides, and superoxides and participates in combustion, corrosion, and redox reactions.
Atomic Properties: Oxygen is a nonmetal, highly electronegative (3.44 on the Pauling scale), and reactive.
Physical Properties: At standard temperature and pressure, it is a gas with a boiling point of −183°C and a melting point of −218.8°C.
Physical Data
Density: 0.001308 g/cm3
Melting Point: 54.36 K (−218.79 °C, −361.82 °F)
Boiling Point: 90.188 K (−182.962 °C, −297.332 °F)
Triple Point: 54.361 K at 0.1463 kPa
Critical Point: 154.581 K at 5.043 MPa
State at 20ºC: Gas
Heat of Fusion: 0.444 kJ/mol for O2
Heat of Vaporization: 6.82 kJ/mol for O2
Molar Heat Capacity: 29.378 J/mol·K for O2
Atomic Data
Atomic Radius: 1.52 Å
Covalent Radius: 0.64 Å
Van der Waals Radius: 1.55 Å
Electron Affinity: 140.976 kJ/mol
Electronegativity: (Pauling scale): 3.44
1st Ionization Energy: 1313.942 kJ/mol
2nd Ionization Energy: 3388.671 kJ/mol
3rd Ionization Energy: 5300.47 kJ/mol
Oxidation States: -2, -1 (common), +2, +1 (uncommon)
Crystal Structure: Cubic
Magnetic Ordering: Paramagnetic
Abundance and Sources
Oxygen is one of the most abundant elements in the universe and on Earth.
- Earth’s Atmosphere: Oxygen makes up approximately 21% by volume.
- Earth’s Crust: The most abundant element by mass (~46%).
- Universe: The third most abundant element after hydrogen and helium.
- Formation in Stars: Oxygen is produced in the cores of stars through stellar nucleosynthesis, primarily by the triple-alpha process followed by fusion of helium and carbon.
Commercially, oxygen comes from fractional distillation of liquefied air, electrolysis of water, and separation membranes.
Biological Role, Health Effects, and Toxicity
Oxygen is essential for life but is toxic in high concentrations.
- Biological Role: Oxygen is vital for cellular respiration in aerobic organisms and is involved in the biosynthesis of numerous organic molecules.
- Health Effects: While essential for life, excessive oxygen can lead to oxygen toxicity, damaging lung tissues and the central nervous system.
- Toxicity to Organisms: Some anaerobic organisms find oxygen toxic due to its oxidative properties.
Uses of Oxygen
From breathing to industrial processes, oxygen has a wide array of applications.
Environmental: Supports combustion in waste incineration.
Respiration: Essential for life in animals and aerobic microorganisms.
Industrial Applications:
- Steelmaking and welding.
- Production of synthetic chemicals like ethylene oxide.
Medical Uses:
- Treating hypoxia and carbon monoxide poisoning.
- Oxygen therapy in hospitals.
Aerospace: As an oxidizer in rocket fuel.
Water Treatment: Oxidizes impurities.
Interesting Oxygen Facts
- Oxygen is a colorless, tasteless and odorless gas, but liquid oxygen has a distinct blue color.
- Liquid oxygen is magnetic and can be suspended between the poles of a magnet.
- Oxygen was the first gas to be cooled to a liquid state (in 1877).
- Ozone has a distinct smell, often described as “electric,” noticeable during thunderstorms.
- Oxygen makes up about 21% of the air you breathe by volume.
- Nearly half the Earth’s crust is oxygen by mass.
- Oxygen is the most abundant element in the human body accounting for 65% of your weight.
- All animals and plants require oxygen to live.
- Oxygen is not flammable. However, it supports combustion of other materials and should not be stored near flammable materials.
- Oxygen readily dissolves in water. This property makes life underwater possible.
- Oxygen gas is important in the steel industry for making steel. It is also a key ingredient in the manufacture of hydrogen peroxide and nitric acid. The compound epoxyethane is produced to make the common polymers polyester and PVC (polyvinylchloride)
- The green waves of color in the auroras result from the ionization of oxygen in the upper atmosphere.
- Oxygen rarely occurs in pure form in nature. Oxygen bonds to itself to form diatomic O2. Ozone is another pure oxygen molecule with formula O3.
- Ozone absorbs harmful ultraviolet radiation from the Sun in the upper atmosphere. Closer to the ground, however, ozone is a pollutant and is hazardous to life.
- Oxygen was the standard for measuring the atomic weights of other elements until 1961. It was replaced by the mass of carbon-12.
Learn more about elements on the periodic table.
References
- Best, Nicholas W. (2015). “Lavoisier’s ‘Reflections on Phlogiston’ I: Against Phlogiston Theory”. Foundations of Chemistry. 17 (2): 137–51. doi:10.1007/s10698-015-9220-5
- Brown, Theodore L.; LeMay, Burslen (2003). Chemistry: The Central Science. Prentice Hall/Pearson Education. ISBN 978-0-13-048450-5.
- Emsley, John (2001). “Oxygen”. Nature’s Building Blocks: An A–Z Guide to the Elements. Oxford, England: Oxford University Press. ISBN 978-0-19-850340-8.
- Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8
- Marples, Frater James A. “Michael Sendivogius, Rosicrucian, and Father of Studies of Oxygen“. Societas Rosicruciana in Civitatibus Foederatis, Nebraska College.