You may not know: Astatine is the rarest natural element on Earth

Astatine is the rarest element that occurs naturally in the Earth’s crust with less than 25 g of 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 is named after the Greek word “less stable “. It is radioactive with a half-life of just over 8 hours , even in its most stable form, astatine-210 . That means even if you collect some, after 24 hours it’s only 1/8 as astatine decays to bismuth-206 or polonium-210 .

You may not know: Astatine is the rarest natural element on Earth
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. The radioactivity of astatine is so high that if you had enough to see with the naked eye, it would evaporate under its own heat. Scientists can only work directly with astatine through artificial production by nuclear reaction, usually using alpha particles to bombard bismuth-209.

Therefore, most of what we know about the element comes from theoretical research rather than practical experiments . For example, researchers think that astatine looks like a black solid because it is located in the halogen column of the periodic table. The heavier the elements in the halogen column, the darker the color. Colorless fluorine, yellow-green chlorine, red-brown bromine, dark gray-violet iodine. So, logically, the next element, astatine, should get darker.

Whether astatine is more like a metal or a nonmetal is controversial among chemists because it lies along the diagonal of the periodic table, containing metalloids such as 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 may have some important practical applications . When the element decays, it emits alpha particles, radioactive particles that form from the combination of two protons and two neutrons. For several reasons, alpha particles are very effective at targeting cancer cells. According to Mehran Makvandi, a radiologist at the University of Pennsylvania’s medical school, astatine emits fewer alpha particles than other isotopes like actinium-225. The element also emits only alpha particles, which are the least toxic type of radiation.

If scientists can attach astatine isotope to a molecule that looks for cancer cells, they could create a cancer therapy that doesn’t harm surrounding tissue. Since astatine is so rare and unstable, it’s not an easy task.