A Level Chemistry OCR Practice Exam

Which of the following correctly defines homolytic fission?

1. Breaking a bond and forming new bonds simultaneously

2. Breaking a bond equally between two atoms

3. Forming a bond between ions

4. Breaking a bond leaving one atom with both electrons

The correct answer is: Breaking a bond equally between two atoms

The correct definition of homolytic fission is breaking a bond equally between two atoms. In homolytic fission, a covalent bond is split such that each of the two atoms involved in the bond retains one of the bonding electrons. This results in the formation of two radicals, each containing an unpaired electron. This process is crucial in many chemical reactions, particularly those involving radical mechanisms, where the radicals can further react with other molecules, facilitating a variety of reactions in organic chemistry. The emphasis on equal distribution of electrons is what defines it distinctly from other types of bond cleavage, such as heterolytic fission, where one atom retains both electrons from the bond, leading to the formation of ions. In contrast, the other options describe different processes. For instance, breaking a bond and forming new bonds simultaneously refers to a different reaction mechanism, such as a concerted mechanism. Forming a bond between ions does not relate to fission at all. Breaking a bond and leaving one atom with both electrons characterizes heterolytic fission rather than homolytic fission. Thus, option B accurately represents the concept of homolytic fission in chemical reactions.