Polonium (Po) is an element known for its intense radioactivity and notorious history. Its existence highlights a fundamental concept in chemistry: the identity of an element is solely determined by the number of protons in its nucleus. Understanding this specific count provides the foundation for comprehending Polonium’s unique physical behavior and atomic structure.
The Defining Number: Protons in Polonium
Polonium, symbolized as Po, possesses exactly 84 protons in the nucleus of every atom. This number, 84, is the atomic number (Z), which acts as the element’s distinct identifier on the periodic table. If an atom were to gain or lose a proton, it would instantly transform into a different element altogether, such as Bismuth (83 protons) or Astatine (85 protons). The proton count is fixed for Polonium, but the number of neutrons can vary, which leads to the existence of different isotopes. Protons and neutrons together determine the atomic mass of an atom, with the most common isotopes of Polonium having an approximate atomic mass of 209 atomic mass units.
What Makes Polonium Unique
Polonium was the first element discovered solely by its radioactivity, isolated by Marie and Pierre Curie in 1898 from the uranium ore pitchblende. The element was named in honor of Marie Curie’s native country, Poland. It is a rare, silvery metal located in Group 16 of the periodic table, sometimes classified as a metalloid or chalcogen, sharing properties with elements like tellurium. Polonium is extremely scarce in nature, occurring only in minute traces as a decay product of uranium. Its physical state is a solid at room temperature, with a relatively low melting point of 254 degrees Celsius.
Radioactivity and the Role of Isotopes
The variability in the number of neutrons results in Polonium having over two dozen known isotopes, all of which are radioactive. Isotopes are atoms of the same element that have the same number of protons but differ in their neutron count. The most notable isotope is Polonium-210 (Po-210), which has 84 protons and 126 neutrons, giving it an atomic mass of 210.
Polonium-210 is significant due to its short physical half-life of about 138 days and its powerful emission of alpha particles. Alpha radiation consists of two protons and two neutrons, identical to a helium nucleus, and does not penetrate the outer layer of skin.
However, if Po-210 is ingested or inhaled, the alpha particles are highly damaging to internal tissues, making the isotope extremely toxic. This intense radioactivity has led to limited, specialized uses, such as in antistatic devices or as a heat source for spacecraft. Despite these applications, Polonium-210 is most infamous for its extreme toxicity, being many times more poisonous than cyanide once inside the body.