How does the half redox reaction 3Br2 -> 2Br3- become Br2 + 2e- -> 2Br-?
Good question. First I’ll have to say that the first reaction you have written appears to be incorrect. Bromine is able to take up one electron to form Br^-, but it is incapable of becoming a -3 ion. That is because there is only one position left for an electron in the 4th energy level of bromine. To put 3 electrons into the atom you would need to use the fifth energy level and the charge on the bromine nucleus simply will not retain extra electrons in the that higher energy level. If you look at the first link you will see much information about bromine and its ions. There is no mention of a -3 ion of bromine. The second reaction is the typical half reaction for the reduction of bromine to bromide ion. The second link shows more information about the half-reaction of bromine. Hope this is helpful.
