Did you know: Astatine is the rarest natural element on Earth?

Astatine is the rarest naturally occurring element in the Earth's crust with less than 25 grams present on the entire planet at any given time .

Astatine is so rare that scientists still don't know basic information about the element, like what it looks like. Astatine gets its name from the Greek word for "unstable ." It's a radioactive element with a half-life of just over eight hours , even in its most stable form, astatine-210 . That means even if you collect some, after 24 hours, you'll only have one-eighth of it left because the astatine decays into bismuth-206 or polonium-210 .

Researchers still do not know basic information such as the shape of astatine. (Photo: iStock).

Most astatine isotopes have half-lives of less than one second. Astatine is so radioactive that if you had enough of it to see with the naked eye, it would vaporize under its own heat. Scientists can only work with astatine directly through artificial nuclear production, usually by bombarding bismuth-209 with alpha particles.

As a result, most of what we know about the element comes from theoretical research rather than practical experiments . For example, researchers believe that astatine looks like a black solid because it is in the halogen column of the periodic table. The heavier the elements in the halogen column, the darker they are. Fluorine is colorless, chlorine is yellow-green, bromine is red-brown, iodine is dark gray-purple. So, logically, the next element, astatine, would be even darker.

Whether astatine is more of a metal or a nonmetal is a matter of debate among chemists because it lies diagonally across the periodic table, along with metalloids like boron and silicon. In chemical reactions, it sometimes behaves like a halogen and sometimes like a metal, making it difficult for experts to classify.

Although extremely rare , astatine could have some important practical applications . When the element decays, it emits alpha particles, radioactive particles formed by the combination of two protons and two neutrons. For a variety of reasons, alpha particles are very effective at targeting cancer cells. According to Mehran Makvandi, a radiologist at the University of Pennsylvania School of Medicine, astatine emits fewer alpha particles than other isotopes such as actinium-225. The element also emits only alpha particles, which are the least harmful form of radiation.

If scientists could attach an astatine isotope to a molecule that targets cancer cells, they could create a cancer treatment that would not harm surrounding tissue. Because astatine is so rare and unstable, that would be no easy task.