The entirety of the known universe is made up of just 118 elements arranged in innumerable formations and combinations. Some of the most common elements, like hydrogen and carbon, are necessary for organisms to survive on Earth. Just hydrogen and helium make up nearly ninety-eight percent of the mass of the visible universe, leaving only two percent for the other 116 elements. Thus, one can only imagine how uncommon the rarest elements in the universe are. However, these elements have unique properties, and they can be used in a variety of fields, including medicine and technology.
Promethium (Pm), otherwise known as element 61, is an extremely rare element part of the lanthanide group. Elements in this group are silvery, soft, and reactive metals. The lanthanides, along with scandium and yttrium, are known as rare-earth elements. All elements have their isotopes. Isotopes are variants of the same element with the same number of protons but a different number of neutrons to change the atomic mass. All of the promethium’s isotopes are radioactive, so the elements often decay in nature. This is why only 500-600 grams of it exist on Earth at any given moment. Most of this element has been created artificially, though because it can exist naturally, it is included in this list (as opposed to solely synthetic elements like oganesson). Promethium is mostly used in scientific research, though it is used in small quantities in atomic batteries.
Protactinium (Pa), also known as element 91, is an element in the actinide group. All actinides are radioactive and spontaneously ignite in the air when in powder form. Protactinium’s most stable isotope, 231Pa, exists in extremely small quantities in uranium deposits. Protactinium-231 is a decay product of uranium-235, explaining its location. Protactinium currently has no uses outside of scientific research. Due to the extremely low abundance of the elements in this list, it is difficult to determine which elements are more abundant than others; therefore, the list is not in exact order.
Technetium (Tc), otherwise known as element 43, is a radioactive transition metal. It is the first element to be created synthetically and is the lightest radioactive element. It is created naturally as a byproduct of fission between uranium ore and thorium ore. Because the transition metals are such a broad group, they can differ greatly, though all of them have high melting and boiling points. Technetium-99m, an isotope of the elements, emits gamma rays, which are useful for medical diagnostics. Technetium, in small amounts, is also useful for inhibiting corrosion on steel.
Francium (Fr), also known as element 87, is a radioactive alkali metal known for being the most expensive naturally occurring element at one billion dollars per gram. Alkali metals are known for having one valence electron. This electron is what makes them react violently with water. The larger the element, the more explosive the reaction. Though it is impossible to gather enough francium to observe a reaction with water, it is widely expected that such a reaction would be extremely explosive. Francium also has an extremely short half-life of 22 minutes, meaning that it will decay to half its original value in just 22 minutes. Due to this property, francium currently has no uses. Scientists estimate that there are only about 30 grams of francium in the world at any given moment. It is created by bombarding radium with neutrons in a nuclear reactor.
Finally, astatine (At), otherwise known as element 85, is a highly radioactive element. Strangely, it can act like a halogen or a metalloid depending on the reaction. Astatine’s name is derived from the Greek word “astatos”, meaning unstable. Astatine-211 has a half-life of just 8 hours. There are only about 25 grams of astatine existing on Earth at once, thus making it the rarest element in the known universe. Due to its short half-life, there are only a few uses for the element. However, medical research has shown it to be useful in cancer treatment. When astatine eventually decays, it emits an α particle, composed of two protons and two neutrons. These particles can slice through the strands of a cancer cell’s DNA. When astatine isotopes are attached to cancer-detecting molecules, the α particles could kill the cancer cells without causing damage to surrounding healthy cells. Though other elements also emit this particle, astatine-211 shows the most promise to oncologists due to a number of reasons. Elements have so many interesting properties, from hydrogen to astatine, and further research can open so many more doors in so many different fields.