Polonium (revised)

POLONIUM (REVISED)

Note: This article, originally published in 1998, was updated in 2006 for the eBook edition.

Overview

Polonium was discovered in 1898 by Polish-French physicist Marie Curie (1867-1934) and her husband, Pierre (1859-1906). They were looking for the source of radioactivity in a naturally occurring ore called pitchblende. Radioactivity is the process by which materials give off energy and change into new materials.

Polonium is the heaviest element in the chalcogen family. It is in Group 16 (VIA) on the periodic table. The periodic table is a chart that shows how chemical elements are related to one another. The other chalcogen elements are oxygen, sulfur, selenium, and tellurium.

SYMBOL
Po

ATOMIC NUMBER
84

ATOMIC MASS
208.9824

FAMILY
Group 16 (VIA)
Chalcogen

PRONUNCIATION
puh-LO-nee-um

Polonium is a relatively rare element. The pitchblende studied by the Curies contained only about 100 micrograms (millionths of a gram) of polonium per metric ton of ore. The element can now be prepared artificially in a particle accelerator, or "atom smasher." It causes small particles such as protons, to move at very high speeds. These speeds approach the speed of Light—300,000,000 meters per second (186,000 miles per second). The particles collide with targets, usually gold, copper, or tin. When struck by the particles, the targets break apart, forming new elements and other particles.

Polonium has a few commercial uses. For example, it is used to remove static electrical charges in certain industrial operations. The element is highly toxic.

Discovery and naming

In 1898 French physicist Antoine-Henri Becquerel (1852-1908) had discovered a new form of radiation that was similar to light rays. It was found in a uranium ore called pitchblende.

Becquerel's discovery encouraged many scientists to learn more about this radiation. Among these scientists were the Curies. They decided to study pitchblende to learn what was giving off radiation. They knew uranium was one source of the radiation, but the amount they found was too great to come from uranium only.

The Curies purchased pitchblende by the ton. They slowly purified the ore, getting rid of sand, clay, and other elements in the ore. After months of work, they finally isolated an element that had never been seen before. Marie Curie suggested the name polonium, in honor of her homeland, Poland. Polonium is hundreds of times more radioactive than uranium.

Physical properties

Polonium metal has a melting point of 254°C (489°F), a boiling point of 962°C (1,764°F), and a density of 9.4 grams per cubic centimeter.

Chemical properties

Polonium has chemical properties like the elements above it in the periodic table, especially selenium and tellurium. Polonium's chemical properties are of interest primarily to research chemists. Under most circumstances, scientists are more interested in polonium as a radioactive material.

Occurrence in nature

Polonium is produced in nature when other radioactive elements break down. It is so rare, however, that all the polonium needed is now made in particle accelerators.

Isotopes

Polonium has 27 isotopes, more than any other element. All of these isotopes are radioactive. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope.

A radioactive isotope is one that breaks apart and gives off some form of radiation. About the only isotope of any use is polonium-210.

Extraction

Polonium occurs so rarely and has so few uses that it is extracted from natural ores only for the purpose of research.

Uses

Polonium releases a great deal of energy during its radioactive breakdown. This has led to the development of compact heat sources for specialized purposes, such as use on space probes.

Radiation is used to remove static electricity from photographic film. Static electricity consists of electric charges that collect on the outside of a surface. In film, they can reduce the clarity of a picture. The radiation polonium releases creates electrical charges in the air around it. These charges combine with those on the film, neutralizing them and preventing damage to the film.

Compounds

There are no compounds of polonium of practical interest. Some polonium compounds are prepared for the purpose of research.

Health effects

Polonium is an extremely dangerous substance. When it breaks down, it gives off alpha particles. These particles are tiny, atom-sized particles that can destroy cells. Polonium is considered to be more than 100 billion times more dangerous than hydrogen cyanide. The maximum suggested exposure to the element is no more than about seven one-hundred-billionths of a gram.

Polonium is an extremely dangerous material. It has recently been found in the tobacco used in cigarettes.

A relatively new hazard of polonium has recently been identified. The element has been found in the tobacco used in cigarettes and other products. The amount of polonium taken in by a smoker is approximately equal to that taken in from all other sources. Polonium must be added, therefore, to the list of harmful chemicals inhaled during smoking.