Why is AgCl light sensitive?
I had always assumed that light catalysed the reaction as AgCl is quite stable in the dark. A web search revealed a bit more information. AgCl consists of crystals of tightly packed ions of silver and chlorine, denoted Ag+and Cl-. When film containing Ag+ and Cl- is exposed to light energy, the chlorine ion’s extra electron is ejected and then captured by a silver ion. Electron ejected from chlorine (Oxidation): Ag+ + Cl- + light energy → Ag+ + Cl + 1 electron Electron captured by silver (Reduction): Ag+ + 1 electron → Ag (metal) When silver metal is produced as a result of the electron capture, it forms a dark image on film. Ag+ has been reduced to Ag (metal), and Cl- has been oxidised. I suspect it is a bit more complicatedthan this as AgCl is not a true ionic compound, but somewhere between ionic and covalent. It will be interesting to see if any further information emerges. An interesting question!
