Classification of Oxygen
Oxygen is classified as a non-metal. Non-metals typically lack metallic luster, are poor conductors of electricity and heat, and tend to gain electrons in chemical reactions. Oxygen exhibits these characteristics. It is located in Group 16 (Chalcogens) and Period 2 of the periodic table.
Observable Physical Characteristics
Color and Texture
At standard temperature and pressure, oxygen gas (O₂) is colorless, odorless, and tasteless. This makes its presence undetectable by human senses alone. When cooled to its liquid state, liquid oxygen (LOX) appears as a pale blue, transparent fluid. Upon further cooling to a solid state, solid oxygen also retains a pale blue appearance.
State of Matter at Room Temperature
At typical room temperature, which is generally considered to be between 20 °C and 25 °C (68 °F and 77 °F), oxygen exists as a gas. This gaseous form is essential for respiration in most living organisms on Earth.
Density and Solubility
Oxygen gas is slightly denser than air. This property is significant in various contexts; for example, in some confined spaces or deep mines, oxygen levels can be affected by the stratification of gases. Oxygen is also sparingly soluble in water. This solubility, though low, is critical for aquatic life globally, enabling fish and other organisms to respire in oceans, rivers, and lakes from the Arctic to the tropics.
Thermal Properties
Melting Point
Oxygen transitions from a solid to a liquid state at its melting point. The melting point of oxygen is approximately -218.79 °C.
Boiling Point
Oxygen changes from a liquid to a gaseous state at its boiling point. The boiling point of oxygen is approximately -182.95 °C. These extremely low temperatures are why liquid oxygen is stored in specialized cryogenic containers and used in applications such as rocket propellant, exemplified by its use in space programs worldwide from the Kennedy Space Center in the United States to the Baikonur Cosmodrome in Kazakhstan.