Polonium (Po), element 84, occupies a unique space on the periodic table due to its extreme radioactivity. Its chemical family is determined by its location in the periodic table, which dictates its electronic structure. Polonium belongs to Group 16, a collection of elements formally known as the Chalcogens.
Classification: The Chalcogen Family (Group 16)
The Chalcogen family, also called the Oxygen Group, includes oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and polonium (Po). These elements share a common outer electron configuration, specifically possessing six valence electrons in their outermost shell. This arrangement means they are two electrons shy of achieving a stable octet, which strongly influences their chemical behavior.
Polonium is situated at the bottom of this grouping. Metallic properties generally increase as one moves down a column in the periodic table, and the elements above polonium progress from non-metals (oxygen and sulfur) to metalloids (selenium and tellurium). Polonium is often classified as a metal, or sometimes a metalloid, because it exhibits electrical conductivity that decreases as temperature rises, a defining trait of metals.
Its position in Period 6 results in a large atomic size and lower electronegativity compared to the lighter chalcogens. While its chemical behavior shows similarities to its lighter family members, its physical characteristics lean toward metallic neighbors like bismuth and lead. This transitional nature makes polonium the heaviest and most metallic element in the Chalcogen family.
Defining Characteristics: Radioactivity and Toxicity
Polonium’s most defining characteristic is its intense radioactivity. The isotope Polonium-210 (Po-210) is the most common form and is a highly energetic alpha particle emitter. An alpha particle is essentially the nucleus of a helium atom, consisting of two protons and two neutrons.
Polonium-210 has a half-life of approximately 138 days, which is remarkably short for a heavy element, leading to a rapid decay rate. This fast decay causes it to generate substantial heat, about 141 watts per gram, and makes it radiotoxic. Since alpha particles cannot penetrate the outer layer of dead skin cells, polonium poses virtually no threat from external exposure.
The danger arises only if the substance is ingested, inhaled, or enters the body through a wound. Once inside, the short-range, high-energy alpha particles bombard internal tissues, causing rapid damage to DNA and major organs. Due to this internal exposure, Polonium-210 is considered highly lethal, being far more toxic than conventional chemical poisons like cyanide.
Discovery and Practical Uses
Polonium holds a significant place in the history of science, as the first element discovered through radiochemical analysis. Marie and Pierre Curie discovered it in 1898 while investigating the intense radioactivity of the uranium ore pitchblende. Marie Curie named the element polonium in honor of her native country, Poland.
Polonium-210 has a few specialized applications that capitalize on its unique properties. Its intense alpha emission is used in anti-static devices for industrial processes like rolling paper or manufacturing sheet plastics. The alpha particles ionize the surrounding air, which effectively neutralizes static electrical charges.
Another application uses the element’s high heat generation. Its rapid decay produces a lightweight, reliable heat source, which has been explored for use in radioisotope thermoelectric generators (RTGs) to power space equipment. However, its extreme toxicity and short half-life strictly limit its widespread use, requiring specialized handling and containment.