A large variety of organic sulfur compounds is possible because of the ability of the sulfur atom to exhibit many valence states. Sulfur compounds having bivalent, tetravalent, and hexavalent sulfur are known. Organic sulfur compounds are often compared with oxygen compounds, but this can be very misleading. Some of the major differences result from: the ability of sulfur to unite with itself to form chains giving di-, tri-, tetra-, and polysulfides; the lower capacity of sulfur to hold hydrogen and the greater capacity to unite with negative elements; and the ability of sulfur to unite with oxygen and halogens to form such compounds as sulfones, sulfonyl halides, and sulfonic acids. The atomic structure which leads to these properties has been discussed under "sulfur compounds-structure".