Polonium is a chemical element

Chemical element

A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...

 with the symbol Po and atomic number

Atomic number

In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...

 84, discovered in 1898 by Marie Skłodowska-Curie

Marie Curie

Marie Skłodowska-Curie was a physicist and chemist famous for her pioneering research on radioactivity. She was the first person honored with two Nobel Prizes—in physics and chemistry...

 and Pierre Curie

Pierre Curie

Pierre Curie was a French physicist, a pioneer in crystallography, magnetism, piezoelectricity and radioactivity, and Nobel laureate. He was the son of Dr. Eugène Curie and Sophie-Claire Depouilly Curie ...

. A rare and highly radioactive element, polonium is chemically similar to bismuth

Bismuth

Bismuth is a chemical element with symbol Bi and atomic number 83. Bismuth, a trivalent poor metal, chemically resembles arsenic and antimony. Elemental bismuth may occur naturally uncombined, although its sulfide and oxide form important commercial ores. The free element is 86% as dense as lead...

 and tellurium, and it occurs in uranium

Uranium

Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

 ore

Ore

An ore is a type of rock that contains minerals with important elements including metals. The ores are extracted through mining; these are then refined to extract the valuable element....

s. Polonium has been studied for possible use in heating spacecraft

Spacecraft

A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....

. As it is unstable, all isotopes of polonium

Isotopes of polonium

Polonium has 42 isotopes, all of which are radioactive, with between 186 and 227 nucleons. 210Po with a half-life of 138.376 days has the longest half-life of naturally occurring polonium. 209Po with a half-life of 103 years has the longest half-life of all isotopes of polonium...

 are radioactive. There is disagreement as to whether polonium is a post-transition metal

Post-transition metal

In chemistry, the term post-transition metal is used to describe the category of metallic elements to the right of the transition elements on the periodic table...

 or metalloid

Metalloid

Metalloid is a term used in chemistry when classifying the chemical elements. On the basis of their general physical and chemical properties, each element can usually be classified as a metal or a nonmetal. However, some elements with intermediate or mixed properties can be harder to characterize...

.
Polonium has 33 known isotopes

Isotopes of polonium

Polonium has 42 isotopes, all of which are radioactive, with between 186 and 227 nucleons. 210Po with a half-life of 138.376 days has the longest half-life of naturally occurring polonium. 209Po with a half-life of 103 years has the longest half-life of all isotopes of polonium...

, all of which are radioactive.