Oxygen (O)


  • Symbol: O
  • Atomic Number: 8
  • Atomic Weight: 15.999
  • Element Classification: Non-metal
  • Discovered By: Carl Wilhelm Scheele and Joseph Priestley (independently)
  • Discovery Date: 1774 (Scheele), 1774 (Priestley)
  • Name Origin: Greek: ‘oxy’ (acid, sharp) and ‘genes’ (producer)
  • Density(g/cc): 0.001429 (at 0°C, 101.325 kPa)
  • Melting Point: -218.79°C
  • Boiling Point: -182.962°C
  • Appearance: Colorless gas
  • Atomic Radius(pm): 60


Oxygen was discovered independently by Carl Wilhelm Scheele in Sweden and Joseph Priestley in England around 1774. Scheele produced oxygen by heating mercuric oxide and various nitrates in 1772, but his findings were published later. Priestley is often credited with the discovery as he published his results in 1774, after isolating oxygen by focusing sunlight on mercuric oxide, releasing a gas that enhanced combustion. The name “oxygen” was coined by Antoine Lavoisier from the Greek words ‘oxy’ (acid, sharp) and ‘genes’ (producer), under the mistaken belief that oxygen was a constituent of all acids.

Relation to Other Elements

Oxygen is part of the chalcogen group in the periodic table and is the most abundant element by mass in the Earth’s crust. Its diatomic molecule (O₂) is essential for the respiration of most living organisms and combustion processes. Oxygen forms compounds with almost all other elements and is a key player in the water molecule (H₂O), crucial for life. Its high electronegativity enables it to form strong covalent bonds, making it a fundamental element in organic and inorganic chemistry. Oxygen’s allotropes include O₂ and ozone (O₃), with ozone playing a crucial role in protecting the Earth from ultraviolet radiation.

Natural Occurrence

Oxygen constitutes about 21% of the Earth’s atmosphere, vital for aerobic organisms. It’s the most abundant element by mass in the Earth’s crust, mainly found in the form of oxides and silicates. Oxygen is also a major component of water, which covers about 71% of the Earth’s surface. In the universe, oxygen is generated through the process of stellar nucleosynthesis in stars.


Oxygen’s applications are diverse, reflecting its importance in biological, industrial, and environmental contexts:

  • Medical: Oxygen therapy provides supplemental oxygen to individuals with respiratory disorders or those undergoing medical treatments requiring enhanced oxygen levels.
  • Industrial: Oxygen is used in steelmaking, welding, and cutting processes, as it supports combustion and enhances the efficiency of these operations.
  • Environmental: Ozone (O₃) is used for water purification processes, breaking down pollutants and sterilizing water.
  • Chemical: Oxygen is essential in various chemical synthesis processes and in the production of compounds such as peroxides.
  • Aerospace and Submarine Environments: High-concentration oxygen environments are created for astronauts and submariners, where atmospheric control is critical.

The discovery of oxygen was pivotal in understanding the principles of combustion, respiration, and the composition of the atmosphere, marking a significant advancement in the field of chemistry and broadening our understanding of the natural world. Oxygen’s ubiquitous presence and reactivity make it a cornerstone of life and numerous industrial processes.

Nitrogen (N)

Fluorine (F)