Atomic number: 37

Symbol: Rb

Category: alkali metal

Density at 25°C: solid:  1.532 g·cm−3

This is quite a reactive element in the sense that it reacts with air quite rapidly. Rubidium chloride is used in biochemistry to help take up DNA in cells. Sometimes rubidium compounds are used in fireworks because of their purple colour when burning.

Rubidium in a glass tube with inert gas. image: adapted from wikipedia

Use, natural applications or common combinations: 

  • For atomic clocks 
  • Special cooling for atoms
  • Some compounds tested for effect on bipolar depression.

Basic characteristics:

  • Standard atomic weight: 85.4678(3)
  • Melting point:  39.31 °C
  • Boiling point: 688 °C
  • Radioactivity: almost all stable naturally but one is slightly radioactive
    • 87Rb decays to stable 87Sr half life of a few billion years. about 670 Bq/g, enough to affect photographic film.