293Polonium- Metalloid
Polonium is a chemical element with the symbol Po and atomic number 84, discovered in
1898 by Marie and Pierre Curie. A rare and highly radioactive element with no stable
isotopes, polonium is chemically similar to bismuth and tellurium, and it occurs in uranium
ores. Applications of polonium are few, and include heaters in space probes, antistatic
devices, and sources of neutrons and alpha particles. Because of its position in the
periodic table, polonium is sometimes referred to as a metalloid, however others note that
on the basis of its properties and
behavior it is "unambiguously a metal".
Polonium is 'distinctly metallic' in
some ways, or shows metallic
character by way of:
The metallic conductivity of
both of its allotropic forms.
The presence of the rose-
colored Po2+ cation in aqueous
solution.
The many salts it forms.
The predominating basicity of
polonium dioxide.
The highly reducing conditions
required for the formation of the
Po2– anion in aqueous solution.
However, polonium shows nonmetallic character in that:
Its halides have properties generally characteristic of nonmetal halides (being
volatile, easily hydrolyzed, and soluble in organic solvents).
Many metal polonides, obtained by heating the elements together at 500–1,000
°C, and containing the Po2– anion, are also known.
Toxicity Overview
Polonium is highly dangerous and has no biological role. By mass, polonium-210 is around
250,000 times more toxic than hydrogen cyanide (the actual LD 50 for^210 Po is less than 1
microgram for an average adult (see below) compared with about 250 milligrams for
hydrogen cyanide).
The main hazard is its intense radioactivity (as an alpha emitter), which makes it very
difficult to handle safely. Even in microgram amounts, handling 210 Po is extremely
dangerous, requiring specialized equipment (a negative pressure alpha glove box
equipped with high performance filters), adequate monitoring, and strict handling
procedures to avoid any contamination.
Alpha particles emitted by polonium will damage organic tissue easily if polonium is
ingested, inhaled, or absorbed, although they do not penetrate the epidermis and hence
are not hazardous as long as the alpha particles remain outside of the body.