Portrait shots with Nikon D7000 and Tokina 50-135mm

Just recently bought this camera and lens and really liking them both to use as a combo. I had my first go at taking some portrait shots in the last few weeks and am reasonably happy with the results. The only thing that bothers me is that on quite a few of the pics I managed to get the eyes in focus but not the mouth or ears. I'm new to photography so having to do a lot of experimenting and making a lot of mistakes. Should I use a smaller apature to get the whole face in focus. I took most of the pics at F3.2. Thanks for any advice.

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