|Atomic mass||15.994 amu|
|Date of discovery||1774|
|Name of discoverer||Joseph Priestley|
|Name origin||From the Greek words oxus (acid) and gennan (generate)|
|Obtained from||From liquid air|
Oxygen is the third most abundant element in the universe by mass and is essential to life on Earth.
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.
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.