Understanding Iodine
Classification
Iodine (I) is classified as a non-metal. It belongs to Group 17 of the periodic table, known as the halogens.
Appearance and State at Room Temperature
At standard room temperature (approximately 20-25 °C) and pressure, elemental iodine exists as a solid. It typically presents as a lustrous, dark purple-black crystalline solid. These crystals often have a metallic sheen, leading some to initially mistake it for a metal. When heated, iodine produces a distinctive deep violet vapor.
Key Physical Properties
Melting and Boiling Points
Iodine exhibits specific temperatures at which it undergoes phase transitions. Its melting point is approximately 113.7 °C. Upon further heating, it reaches its boiling point at about 184.3 °C.
Sublimation
A notable physical property of iodine is its tendency to sublime readily. Sublimation is the process where a solid transitions directly into a gas without first passing through a liquid phase. This characteristic is observable even at room temperature, where solid iodine crystals slowly release a violet vapor. This sublimation becomes much more pronounced with increased temperature, making it a common laboratory demonstration. For example, in laboratories worldwide, iodine can be purified through sublimation by gently heating the solid, allowing the vapor to re-solidify on a cooler surface, leaving impurities behind.