Halogen only periodic table group that contains elements in three of the main states of matter at standard temperature and pressure. All of the halogens form acids when bonded to hydrogen. Most halogens are typically produced from minerals or salts. The middle halogens, that is chlorine, bromine and iodine, are often used as disinfectants. Organobromides are the most important class of flame retardants. Elemental halogens are dangerous and can be lethally toxic. The fluorine mineral fluorospar was known as early as 1529. Early chemists realized that fluorine compounds contain an undiscovered element, but were unable to isolate it. In 1860, George
Graphite intercalation compound A stage n magnetic GIC has n graphite layers separating successive magnetic layers. As the stage number increases the interaction between spins in successive magnetic layers becomes weaker and 2D magnetic behaviour may arise. Chlorine and bromine reversibly intercalate into graphite. Iodine does not. Fluorine reacts irreversibly. In the case of bromine, the following stoichiometries are known: CBr for n = 8, 12, 14, 16, 20, and 28. Because it forms irreversibly, carbon monofluoride is often not classified as an intercalation compound. It has the formula (CF). It is prepared by reaction of gaseous fluorine with graphitic carbon at 215–230