How will we write half equations for addition reactions?

For instance C2H4+Cl2->C2H4Cl2

In this case, the oxidation state of chlorine decreases from 0 to -1 and in carbon, it increases from -2 to -1. So how should we write their half equations? I think simplifying will make it look like this: Cl2+2e->2Cl- and 2C2- ->2C-+2e

But what about the full half equations that we see in

http://www.chemguide.co.uk/inorganic/redox/equations.html how will we write them out?

Thanks for the help