Cohalogens

A cohalogen is a diatomic molecule consisting of two different halogen atoms, such as bromine chloride (BrCl) or iodine monochloride (ICl). These compounds are often referred to as interhalogens, though the term cohalogen is more specific to the diatomic species. They are distinct from the homonuclear diatomic halogens like Cl2 or Br2.

Cohalogens are generally synthesized by direct reaction of the constituent halogens, often under controlled conditions to favor the formation of the mixed diatomic molecule. For example, bromine chloride can be prepared by reacting bromine with chlorine.

These compounds are typically reactive and serve as sources of both halogens in various chemical reactions. Their properties, such as melting points and boiling points, fall between those of the individual halogens. For instance, BrCl is a liquid at room temperature, with a boiling point between that of Br2 and Cl2.

The electronegativity difference between the two halogen atoms leads to a polar covalent bond within the cohalogen molecule, making them susceptible to nucleophilic and electrophilic attack. They can undergo disproportionation reactions, forming the individual halogens and other halogen compounds. Due to their reactivity, cohalogens are often handled with care and stored under inert conditions.