Atomic number: 85

Symbol: At

Category: halogen 

Density at 25°C: solid: density: uncertain

This is perhaps one of the rarest and fleeting elements that can naturally occur. It was initially synthesised but then later discovered in nature.  

Use, natural applications or common combinations: 

  • naturally, albeit briefly, occurs in uranium minerals, estimated to only be about 1 gram on earth at anyone time.
  • Francium-223, the father isotope of astatine-219, alpha decays with a probability of only 0.006%, making this astatine isotope extremely rare. 

Basic characteristics:

  • Standard atomic weight: about 210
  • Melting point: 302 °C [estimated, may be lower]
  • Boiling point: 337 °C [estimated]
  • Radioactivity: all radioactive
  • 210At  has half life of 8.1 hours via alpha and beta decay and turns into polonium and bismuth.