Valence electrons for trasition elements?

Can anyone tell me how to figure out the valence electrons for the transition elements? I know Group 1 has 1 valence electron and Group 2 has 2 and so on but I don't know about the middle section of the Periodic Table. For example, I'm trying to figure out how to combine Fe and Cl but I'm unsure how to do that without knowing the valence electrons for Fe.