A Level Chemistry OCR Practice Exam

What effect does electron shielding have on outer-shell electrons?

1. It increases the attractive force from the nucleus

2. It decreases the repulsion between outer-shell electrons

3. It reduces the net attractive force from the positive nucleus

4. It enhances the nucleus's ability to attract all electrons

The correct answer is: It reduces the net attractive force from the positive nucleus

Electron shielding refers to the phenomenon where inner-shell electrons repel outer-shell electrons, which can affect the overall interaction between these outer electrons and the positively charged nucleus. In this context, the correct choice highlights that electron shielding reduces the effective nuclear charge that outer-shell electrons experience. As inner-shell electrons are present, they create a shielding effect that diminishes the attractive force exerted by the nucleus on the outer-shell electrons. Essentially, the presence of these inner electrons means that outer electrons do not feel the full strength of the positive charge from the nucleus. This results in a lower net attractive force, making it easier for outer-shell electrons to be removed, which is significant in explaining trends in ionization energy across periods and down groups in the periodic table. The other options fail to address the fundamental implication of shielding accurately, emphasizing why shielding ultimately leads to a weaker attraction rather than enhancing forces or reducing repulsion between outer electrons.