Reverse shielding effect? It is known that shielding effect causes a reduction in nuclear attraction of electrons,then wont the valence electrons cause a repulsive force on the inner shell electrons and cause a stronger 'attraction' to the nucleus?
 A: The position of electrons in atoms follow probability distributions. Even the outer shell electrons have probabilities of being closer to the nucleus than the inner shell electrons. But in atoms where screening is noticeable, we  have a large number of inner electrons that have a probability of being closer to the nucleus than the few valence electrons that are being screened. That is, a great majority of the time we have an inner region of electrons that form a spherically symmetric region of charge so that any repulsive forces from outer electrons is unnoticeable.
Even though the amount of time that the outer shell electrons are closer to the nucleus is smaller than what the inner shell electrons are, when they do get closer the inner electrons will experience a smaller nuclear charge (greater number of electrons). This means the outer shell electrons will actually have the opposite effect, and push the inner electrons away from the nucleus.
As such, there is no "reverse shielding" effect by the outer electrons on the inner electrons, but to a small degree the opposite is true.
