Atomic number: 92

Symbol: U

Category: actinide 

Density at 25°C: solid: density: 19.1 g·cm−3

Uranium is a  well known naturally widely occurring  element that is weakly radioactive.  Uranium is the only naturally occuring element that can sustain it's own nuclear fission reaction. This means its nucleus can split apart spontaneously and then go on to split another uranium atom nearby. 

A recovered billet of highly enriched uranium. image: adapted from wikipedia

The discovery of uranium as an element is credited to the German chemist Martin Heinrich Klaproth.

Use, natural applications or common combinations: 

  • nuclear reactors energy supply 
  • military uses - depleted uranium ammunition for high density penetration.
  • was used in glazes before knowledge of radioactivity
  • measuring the age of the Earth

Basic characteristics:

  • Standard atomic weight: 238.02891(3)
  • Melting point: 1132.2 °C
  • Boiling point:  4131 °C
  • Radioactivity: all radioactive
    • 238U with a half-life of  4.47 billion years emitting alpha particles (most common, about (99.2739–99.2752%)
    • 235U  with a half-life of  704 million years, spontaneous fission decay process.