Question

Why does the colour become darker in silver halides as we move down the group ?

Answer 1

Dear student... The attraction of covalent molecules is due 'dispersion' interaction. ... Since outer electron shells vastly grow in size in fluorine-iodine row, the efficiency of dispersion interactions grow.The halogens become darker as you go down the group. Fluorine is very pale yellow, chlorine is yellow-green, and bromine is red-brown. Iodine crystals are shiny purple - but easily turn into a dark purple vapour when they are warmed up... Regards