What Causes Iodine Sublimation?

Iodine sublimation is caused by temperatures high enough to break the bonds between the atoms in its crystal lattice in the absence of pressures sufficient to keep them close to one another. At the atmospheric pressures at sea level, these conditions are met at just above room temperature, and thus both iodine sublimation and iodine deposition are readily observed. Iodine is a blue-black solid that sublimes into a purple gas.

Sublimation is a common phenomenon in nature. Water ice sublimates readily, which is why ice cubes left long enough in a freezer visibly shrink. Perhaps the best-known example of sublimation, however, occurs with dry ice, which is solidified carbon dioxide. Dry ice is deliberately used in many settings both because of its ability to keep things very cold without wetting them and because of its relative safety. Iodine crystals are far easier to create and demonstrate sublimation and deposition with, but iodine gas is toxic and dangerous.

Iodine in its elemental form is extremely reactive, but compounds of iodine are very important to human health, particularly the function of the thyroid gland. In these cases, it is actually iodine ions, indicated in compounds as iodide, that are used by the body.