Bismuth (Bi) is a metallic chemical element with atomic number 83. Its only naturally occurring isotope is ²⁰⁹Bi, with 83 protons and 126 neutrons. This isotope was first thought to be stable, but it is actually radioactive with an extremely long half-life: 19 quintillion years!

Since the density of bismuth is fairly close to that of lead, and since bismuth is less poisonous than lead, it is sometimes used as a replacement for lead in things like fishing sinkers and X-ray shields.

Bismuth can be spelled using chemical element symbols: Bi - Sm - U - Th.