Hydrides of the Halogens (Hydrogen halides):
i) All halogens react with hydrogen to form volatile covalent hydrides of formula HX.
ii) These hydrides are called hydracids.
iii) The activity of halogens towards hydrogen decreases from fluorine to iodine.
Hydrogen combines explosively with fluorine even in dark. It combines with chlorine in the presence of sunlight and with bromine on heating. Hydrogen combines with iodine on heating and in presence of a catalyst.
iv) Hydracids are the reducing agents.
v) Except HF, all hydrogen halides are gases. HF is a liquid because of inter molecular hydrogen bonding.
H – F ……. H – F ……. H – F ……. H– F
vi) The acidic character of HX are in the following order.
HF < HCl < HBr < HΙ.