What would happen if an incoming low energy antiproton collided with a hydrogen atom? Would it bounce off because of the orbiting electron or would it annihilate with the proton?
Never mind that this is an antiproton. Just suppose it is a positive charge. What happens?
Without another charge around, the electron is on average centered about the proton.
If a - charge is near, the electron is repelled and the proton is attracted. The electron on average is a little farther from the - charge, and the electric force of repulsion goes down a little. Likewise the proton is a little nearer and the electric force of attraction goes up a little.
So the attraction is a little stronger than the repulsion. The atom is weakly attracted to the - charge. You can use the same reasoning to show the atom would also be weakly attracted to a + charge.
Suppose the - charge is an antiproton. As the charge and atom get closer, the likelihood of the antiproton and proton interacting goes up. But without more information, you can't say how close they will get or how long they will stay close.