What Is the Structure of an Atom of Uranium?

When most people the word "uranium," the first thought is often of military applications and atomic bombs.
But what exactly is it in the structure of uranium that makes it so dangerous?

Physical Description

Uranium is labeled with the symbol "U" on the periodic table of elements. It is part of the actinide series of the table that is presented along the bottom of the other elements.
Uranium has an atomic number of 92, which means it has 92 protons. There are also 92 electrons orbiting the nucleus of the element, including 6 valence electrons. (Valence electrons are those in the outermost orbit, or shell, of the atom.)
The number of neutrons in uranium varies, and can be anywhere from 141 to 146. Most common are 143 and 146.
Uranium metal is a metallic silver color, which can react with air to create a coating of black oxide. After refining, the color changes to a white silver. Uranium is softer than steel, but it is also one of the densest metals, almost on par with the density of gold.
The atomic radius of uranium (defined as the width of the atom itself) is 138.5 pm. (A picometre is one trilllionth of a metre.)
Uranium melts at 2070 degrees F, and boils at 7468 degrees F.

Isotopes

An isotope of uranium is defined by the number of neutrons in the atom. (The number of protons and electrons remain the same.)
None of the uranium isotopes are stable, meaning that they can all be destroyed by the process of radioactive decay (the process of losing energy by emitting radiation).
Uranium-234 is one of the naturally occurring isotopes, and is created after the decay of uranium-238. However, it exists in much smaller quantities because of the rate of decay; 234 decays much faster than 238.
Uranium-235, another naturally occurring isotope, is a fissile. Fissiles are capable of creating and often sustaining the chain reactions of nuclear fission. This is the isotope that is used in nuclear reactors and nuclear weapons, capable of generating vast amounts of energy. Less than 1 percent of uranium that occurs naturally forms this isotope, and in order to collect enough to power these weapons and power plants, the uranium must be produced artificially.
Uranium-236 is a product of 235, created when fission does not take place and the atom emits gamma radiation that results in the creation of the new isotope.
Uranium-238 is the most commonly occurring isotope in nature, and it is also used in nuclear reactions. When hit with neutrons, the atom becomes uranium-239, which is very unstable. Within less than 25 minutes, uranium-239 will decay into neptunium-239, which will then decay into plutonium-239. The plutonium-239 is a common component in both nuclear reactors and weapons.

History

The discovery of uranium is credited to Martin Heinrich Klaproth, a German chemist born in 1743. An apothecary who worked in pharmacies across Germany, he was instrumental in revolutionizing developments in mineralogy and analytical chemistry. In 1789, he discovered the first uranium atom, in pitchblende (now known as uraninite, the ore that produces uranium).
A sample of uranium was not isolated until 1841, by French chemist Eugene-Melchior Peligot. Originally, it was believed that uranium existed as a black powder, but with Peligot's work, he found the silvery metallic metal that is recognized as uranium today.
It was another French scientist that discovered the radioactive properties of uranium. Henri Becquerel won the Nobel Prize in 1903 for his discoveries of radioactivity, a prize that was shared with Pierre and Marie Curie. His discovery came in 1896, when he was experimenting with the phosphorescent qualities of uranium.
In 1934, work investigating the possibilities of uranium as both a fuel source and a weapon were begun in earnest. Italian scientist Enrico Fermi--another Nobel Prize winner for his work with radioactivity--was instrumental in creating the groundwork for the first nuclear reactors.
The Manhattan Project began in 1939, further exploring the properties of radioactivity and playing a monumental role in the arms race that took place surrounding World War II, as countries across the world raced to be the first to harness the power of nuclear weapons.

Civilian Uses

Uranium is a valuable resource in terms of its energy production. Because several of its isotopes can be used in fission reactions that create an amazing amount of energy, it has been seen as a viable energy source. The first nuclear reactor was built in 1951, when it was first used to power four lightbulbs. Later, it became the first plant to provide energy to sustain an entire town. Now, a kilogram of uranium can produce the same amount of energy as 1500 tons of coal.
Before the dangers of uranium were discovered, it was a component in many other processes. In the Middle Ages, the compound known as pitchblende (the compound that uranium was discovered in) was used in the glassmaking industry as a colorant to create a yellowish-green shade in glass and ceramics. The dyes created from uranium have also been used in leathermaking. It has also been used in dentures and chemicals in early photographic processes.

Finding Uranium

Uranium is more common in nature than tin and mercury, and can be found in limited quantities in all rock and soil. It is always found in combination with other elements, and can be found combined with a great number of other elements. While forms of uranium occur naturally, in order to get a workable form of uranium, it must first be extracted from the minerals it forms in connection with, and often much go through an enrichment process where the isotopes needed for the final product are created. The form of uranium created through the enrichment process is uranium-235.
Approximately 25 percent of mined uranium is produced in Canada, with Australia and Kazakhstan also producing large numbers.