A Level Chemistry OCR Practice Exam

What are electrons called that are shared among more than two atoms?

1. Localized electrons

2. Delocalised electrons

3. Valence electrons

4. Free electrons

The correct answer is: Delocalised electrons

Electrons that are shared among more than two atoms are referred to as delocalised electrons. This phenomenon occurs in certain bonding scenarios, particularly in molecular structures where the electrons are not confined to a single covalent bond between two atoms but instead are spread out over several adjacent atoms. A prominent example of delocalised electrons can be found in benzene, where the pi electrons are evenly distributed across the carbon atoms, allowing for resonance structures. Localized electrons, in contrast, are associated with specific bonds between two atoms and are not found in a shared state among multiple atoms. Valence electrons are the outermost electrons of an atom concerned in bonding but do not specifically describe the behavior of electrons across multiple atoms. Free electrons typically refer to electrons that are not attached to any atom but are available for conduction, particularly in metals. Therefore, delocalised electrons accurately describes the scenario where electrons are shared among more than two atoms.