Oxygen

Oxygen
Properties
Atomic symbol	O
Atomic number	8
Classification	Non-metal
Atomic mass	15.994 amu
Other Information
Date of discovery	1774
Name of discoverer	Joseph Priestley
Name origin	From the Greek words oxus (acid) and gennan (generate)
Uses	Supports life
Obtained from	From liquid air

Oxygen is the third most abundant element in the universe by mass and is essential to life on Earth.

Chemical Properties

At normal atmospheric pressure oxygen melts at 54.36 Kelvin (K) and boils at 90.2 K; on Earth it essentially exists only as a gas. It readily dissolves in water, which makes aquatic life possible. Under normal conditions oxygen forms molecules consisting of two oxygen atoms each sharing two electrons in the 2p subshell; this form of oxygen is known as O₂. O₂ is a pale blue odourless gas.

Isotopes

There are three stable and 14 radioactive isotopes of oxygen. The stable isotopes are ¹⁶O, ¹⁷O and ¹⁸O, with ¹⁶O being by far the most common. Radioisotopes range from ¹⁰O to ²⁶O, with the two most stable being ¹⁵O and ¹⁴O. This gives oxygen an atomic weight of slightly below 16.