Radicals: Definition, Representation, and Applications
What Are Radicals?
Definition
Radical
A radical is an atom, molecule, cation, or anion that contains an unpaired electron. This unpaired electron makes radicals highly reactive as they seek to pair up their lone electron to achieve a more stable configuration.
Unlike ions, which are charged, radicals are electrically neutral but still highly unstable due to this unpaired electron.
Example
Examples of Radicals:
- Chlorine radical (⋅Cl): A chlorine atom with an unpaired electron.
- Methyl radical (⋅CH₃): A methane molecule missing one hydrogen atom, leaving the carbon atom with an unpaired electron.
- Hydroxyl radical (⋅OH): A hydroxyl group with an unpaired electron on the oxygen atom.
Formation of Radicals: Homolytic Fission (will be covered in more detail in R3.3.2)
- Radicals are commonly formed through homolytic fission, a process in which a covalent bond between two atoms breaks symmetrically, with each atom retaining one of the shared electrons.
- This process requires energy, which can be supplied by ultraviolet (UV) light or heat.
Example
$$
\text{Cl}_2 \xrightarrow{\text{UV light}} \cdot\text{Cl} + \cdot\text{Cl}
$$
In this reaction, UV light provides the energy to break the chlorine-chlorine bond, producing two chlorine radicals.
Note
- When representing homolytic fission, use "fish hook" arrows to show the movement of single electrons.
- Each arrow starts from the bond and ends at the atom gaining the electron.
Representing Radicals
Radicals are represented by placing a single dot (⋅) next to the atom or group of atoms containing the unpaired electron.
Example
- Consider the methyl radical (⋅CH₃).
- Normally, carbon forms four bonds, but in this case, it has three bonds and one unpaired electron.
- The dot next to carbon highlights the unpaired electron, indicating its high reactivity.
Common Mistake
- Radicals are often mistakenly confused with ions.
- Remember, radicals are neutral species with an unpaired electron, while ions are charged species.
