Uranium was named for the planet Uranus and discovered in 1789 by Klaproth. Isolation came in 1841 by Péligot and the radioactivity of the element was noted by Becquerel in 1896.
The pure metal is heavy, silver and lustrous. It tarnishes slowly in air
\[U(s) + O_2(g) \rightarrow UO_2 (s)\]
which at ambient temperatures, \(UO_2\) will gradually convert to \(U_3O_8\). Uranium also reacts with boiling water.
Most of the naturally occurring uranium is the isotope U-238. This form of uranium is not fissionable, i.e., it cannot be used in atomic weapons or power plants. A much smaller percentage of naturally occurring uranium is the isotope U-235, which is fissionable. The process of "enriching" uranium to increase the proportion of U-235 in a sample is expensive and tedious but necessary to produce fuel that is usable in power plants and material for weapons.
The U-238 is not completely useless, however, as it can be "bred" into Pu-239 by bombardment with slow neutrons. This is how weapons-grade plutonium is produced. The use of Pu-239 in power plants is a controversial subject due to its toxicity and the fear of diversion by terrorist groups.
Stephen R. Marsden (ChemTopics)