Astatine

Astatine is the rarest naturally occurring element, only approx. 25 grams of it exists in the entire Earth's crust at any one time, and it is entirely produced by the decay of uranium and thorium. It is the heaviest naturally occurring halogen, highly radioactive, and almost nothing is known about its physical properties because no one has ever seen enough of it to observe.

  • Atomic Number8585 protons, 85 electrons
  • Atomic Mass209.98715 u85× heavier than hydrogen
  • State at Room TempSolidSolid
  • Density7 g/cm³
  • Melting / Boiling301.9°C
  • Discovered1940

What is Astatine?

Astatine has 85 protons and belongs to Group 17 (the halogens). Its most stable isotope, astatine-210, has a half-life of just 8.1 hours. This extraordinary instability means no macroscopic quantity has ever been isolated. Its chemistry has been studied using sub-nanogram amounts in solution. It is predicted to be a dark solid, possibly metallic.

Discovered in 1940 by Dale Corson, Kenneth Ross MacKenzie and Emilio Segrè at the University of California, Berkeley, by bombarding bismuth with alpha particles. Named from the Greek astatos meaning unstable.

Fact If you collected all the astatine that exists naturally in the Earth's crust at any one moment, it would weigh only approx. 25 grams, less than a golf ball. And it would all be gone within a few days as it decays. No other naturally occurring element is as rare.

Where you find Astatine

On Earth

Only a few grams exist in the Earth's crust at any moment. Produced artificially in cyclotrons.

How we use Astatine

  • Targeted radiotherapy.. Astatine-211 is being investigated for cancer treatment, it emits alpha particles that kill cancer cells within a very short range, minimising damage to surrounding healthy tissue.

How it was discovered

Discovered in 1940 by Dale Corson, Kenneth Ross MacKenzie and Emilio Segrè at the University of California, Berkeley, by bombarding bismuth with alpha particles. Named from the Greek astatos meaning unstable.

Deeper dive: astatine properties

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Moving to 86 protons on the periodic table takes us to the next element.