Where would you shoot him? head or chest?
The nose is a pretty good target, if the bear is coming straight at you.
Put lots of shots on target, as the bear closes. Aiming at a shoulder is good, because it usually slows them down and moves them off the line of attack, if you have a powerful enough caliber to break the shoulder.
The brain is a good target because it stops them right now. It is especially viable if they are paused for a moment, very close to you, which happens with some frequency.