I want to get a lens for social photography (groups of people in weddings, or a close up for a bride). What focal length range would be recommendable? Also would it be good to get a wide angle lens for this?
Get a 24-70 F/2.8 zoom (35mm equivalent), if you're serious about wedding photography. Use what you have until you can afford one. (After that, save money for a 70-200mm F/2.8.)
Your question is a bit vague. To just do a group shot, basically any lens will be ok, as long as you can use your feet. However, you want to take into account whether you want to portray the group without context or whether you want to emphasize the group in the surrounding (which you might want to do for a wedding). So sometimes a 50 mm can be fine, while you will use 28-35mm most of the time, and probably even 24mm if you want to catch an impressive builing as well (to increase the percieved size difference of group and surroundings).
To get a close-up with nice aesthetics and proportions I would never go below 50mm (for anything less then head-to-hip), or 105mm for headshots. If close-ups also mean detail shots of the wedding rings, you might end up wanting a macro lens (down the road) as well.
I prefer fixed focal lenses. However, this doesn't work well for weddings, where flexibility is key to capture the event on all levels. If weddings are just something you do next to other things, you can get a set of nice primes that allow you to do anything, but with additional swapping lenses. Since you didn't mention your budget, you might as well go with whatever zoom you have, - subject isolation by low aperture is less important than pressing the shutter at the right time in the right place.
I would think you want to go with a zoom lens. A 28mm to 105 mm is what I always used. Works great especially if you use a dedicated flash and bracket.
I like the wide angle range for a little larger group like a table shot because most times you do not have enough room to back up and using a 105 in my opinion is best for a portrait situation with a couple shot because it compresses the photo more and brings out the crispness and the depth of field is better. Just my experience shooting weddings. When you have a flash mounted on a camera bracket you don't have to worry about shadows or red eye. I hope that helps.
A 28 to 70 is ok but it is much more cost effective to go up to the 105 which is a much better choice for a portrait lens. You get much more lens. I agree with the 2.8 but then again I always used a flash so putting out that extra cost for the 2.8 instead of the 3.5 is also wasteful. Of course if money is no object then get that and then a 105mm as well. I wouldn't think a 70mm will make you happy for background portrait shots. Anyway I hope it works out for you weddings are a tough biz. Tough on the equipment so buy well.