R3.3 Electron sharing reactions

Radical: A radical is an atom, molecule, or polyatomic species that contains an unpaired electron. Radicals are electrically neutral but highly reactive because they seek to pair their unpaired electron to achieve a more stable configuration.

Radicals are represented by placing a dot (•) next to the atom carrying the unpaired electron. They can be:

• Atomic radicals , e.g., $\text{Cl}•$ or $\text{H}•$
• Polyatomic radicals , e.g., $•{\text{CH}}_3$ (methyl radical) or $•\text{OH}$ (hydroxyl radical)

Homolytic fission: Homolytic fission is the breaking of a covalent bond in which each atom retains one of the two shared electrons, producing two radicals.

This is in contrast to heterolytic fission, where both electrons go to one atom, producing ions. In homolytic fission, bond breaking is symmetrical.

Steps in homolytic fission:

1. A covalent bond absorbs energy (from UV light or heat).
2. The bond breaks symmetrically , one electron goes to each atom.
3. Two radicals are produced.

${\text{Cl}}_2\stackrel{\text{UV light}}{\to }\text{Cl}•+\text{Cl}•$

The movement of single electrons in homolytic fission is shown using fish hook arrows , these are single-barbed (half-headed) arrows, one for each electron moving to its respective atom.