Atomic number: 19

Symbol: K

Category: metal

Density at 25°C: solid

Potassium is a highly reactive metal as an element and quite soft. However, as an ion K+, in biology, it is critical for many functions .  It has the symbol K because it comes from the latin Kalium which means potash, which in turn is the alkali that comes from plants. Which is originally where it was used.

A spherical sample of potassium in paraffin oil. image adapted from wikipedia

Use, natural applications or common combinations: 

  • For neurone cells transmitting information.
  • minerals like carnallite, langbeinite, polyhalite

Basic characteristics:

  • Standard atomic weight: 39.0983(1)
  • Melting point: 63.38 °C
  • Boiling point: 759 °C
  • Radioactivity: most are stable
  • 40K is important for radio dating rock samples with a half life of 1.248×109 years major source of natural radioactivity in people (0.012%) decaying via beta-