Known to be behind the characteristic odor of rotting eggs, sulfur is essential for all living cells. Cells make proteins that form strong chemical bonds called disulfide bridges between two adjacent sulfur atoms. These bridges give strength to our hair, outer skin, and nails. Eggs are loaded with sulfur because disulfide bridges are needed to form feathers, which explains why eggs smell on rotting. Because sulfur is easy to smell, natural gas lines–which are normally odorless–have sulfur additives to help people identify and smell a gas leak when it occurs.
Sulfur burns with a blue flame concomitant with formation of sulfur dioxide, notable for its peculiar suffocating odor. Sulfur is insoluble in water but soluble in carbon disulfide and, to a lesser extent, in other nonpolar organic solvents, such as benzene and toluene.
The first and the second ionization energies of sulfur are 999.6 and 2252 kJ·mol−1, respectively. Despite such figures, the +2 oxidation state is rare, with +4 and +6 being more common.
The fourth and sixth ionization energies are 4556 and 8495.8 kJ·mol−1, the magnitude of the figures caused by electron transfer between orbitals; these states are only stable with strong oxidants as fluorine, oxygen, and chlorine.