If you throw a ball in space will you move?

Yes. According to Newton's third law of physics, a force exerted by one body (you) onto another body (the ball), will always have a returning force equal in magnitude and opposite in direction. In simpler terms, the force that you apply to the ball by pushing it will also be applied to you by the ball. However, because the ball has less mass, the ball will gain significantly more speed than you will.