Most common isotopes: U-234 (0.0054 percent natural abundance), U-235 (0.7204 percent natural abundance), U-238 (99.2742 percent natural abundance).

Number of isotopes (atoms of the same element with a different number of neutrons): 16, 3 naturally occurring.

Melting point: 2,075 degrees Fahrenheit (1,135 degrees Celsius).

Density: 18.95 grams per cubic centimeter.

Atomic weight (average mass of the atom): 238.02891.

Atomic symbol (on the Periodic Table of Elements): U.

Atomic number (number of protons in the nucleus): 92.

Uranium (Image credit: Andrei Marincas Shutterstock) Becquerel shared a Nobel Prize with Marie and Pierre Curie in 1903 for the discovery. To his surprise, the plate fogged up, indicating some sort of emissions from the uranium salts. In 1897, French physicist Henri Becquerel left some uranium salts on a photographic plate as part of some research on how light influenced these salts. In fact, uranium was the element that made the discovery of radioactivity possible. Uranium is naturally radioactive: Its nucleus is unstable, so the element is in a constant state of decay, seeking a more stable arrangement. To understand uranium, it's important to understand radioactivity. (An isotope is a version of the element with a differing number of neutrons in its nucleus.) This radioactive metal is unique in that one of its isotopes, uranium-235, is the only naturally occurring isotope capable of sustaining a nuclear fission reaction. This was the first-ever use of an atomic bomb in warfare, and it used one famous element to wreak its havoc: uranium.

Space engineers where to find uranium