For each BodyPart 2x a week, 6 days training is really the day to go...but most can only stand that type of regimin for 6-8 weeks. Thats usually enough to make the gains though. If you want to plan it all out on a calender, a 9 day rotation is better for more frequent usage. It may go something like this:
1: Chest (heavy)
2: Bi's/Back (light)
3: Legs (heavy)
4: Off
5:Tri's/Shoulders
6: Chest (light)/Bi's
7:Back(heavy)/Shoulders (light)
8:Legs (light)/Tri's
9: Off
For light vs. heavy, compound motions and low reps could root your regemin on those days. Chest would include lockouts and 3-4 rep sets for flats, maybe heavy incline flys, etc. Light day would be hammer presses high reps, high rep flys, etc. Shoulder light would have no pressing motions, only laterals and traps. Legs would follow the same logic, as well as back.
The thing about a 2x routine is that you have to attack the compound motions and then let them rest, preferably the legs BEFORE your day off. The hardest day should be recognized, in this case day two because of the heavy chest, but those Bi's and light back are all isolation motions. If you really want to get into it, plan your protien and carb intakes to recover/recoup/reload compared to your workload. This way you can avoid heavy protein overload or unneeded carbs on some days.