A Level Chemistry OCR Practice Exam

How does electron shielding influence chemical reactivity?

1. It enhances the attraction between outer and inner electrons

2. It reduces the effective nuclear charge experienced by outer electrons

3. It increases the ionization energy of electrons

4. It stabilizes reactive intermediates in a reaction

The correct answer is: It reduces the effective nuclear charge experienced by outer electrons

Electron shielding refers to the phenomenon where inner shell electrons partially block the attractive force exerted by the positively charged nucleus on the outer shell electrons. This results in outer electrons experiencing a reduced effective nuclear charge, which is the net positive charge felt by an electron after accounting for shielding by other electrons. When considering chemical reactivity, the lower effective nuclear charge means that outer electrons are less tightly held by the nucleus. This reduction in attraction makes it easier for these outer electrons to be involved in chemical reactions, as they can be lost or shared more readily with other atoms. For example, elements with more inner electron shells typically have higher reactivity, as their outermost electrons are less influenced by the nucleus. The other choices do not accurately reflect the effect of electron shielding on chemical reactivity. Enhancing the attraction between outer and inner electrons does not occur due to shielding; instead, shielding weakens this attraction. While increased ionization energy indicates that electrons are held more tightly, this contradicts the role of shielding, which leads to easier removal of outer electrons. Lastly, while stabilizing reactive intermediates can be important in some reactions, it is not directly related to the concept of electron shielding in the context of general chemical reactivity.