Difference Between Free Radical and Ion

[BSHC]

Difference Between Free Radical and Ion

Last updated on: February 21, 2015

 

  

Free Radical vs Ion
 

The difference between free radical and ion can be explained from the basic properties of an ion and a free radical. 

An ion can be a molecule or atom with a charge (positive or negative) due to loss or gain of an electron.

Ions hold a negative charge due to gain of an electron and hold a positive charge due to loss of an electron.

Ions can be single or multi-charged, depending on the number of electrons gained or lost.

Free radicals are molecules or atoms that has at least one unpaired electron.

This article is about the differences between free radicals and ions including their special characteristics.

What is a Free Radical?

A Free radical is an atom or a group of atoms containing one or more unpaired electron(s).

They are highly reactive due to the presence of an unpaired electron. Free radicals are very unstable and try to gain the stability by accepting the needed electron. They react with other chemical compounds by capturing the needed electron. Free radicals are important intermediates in natural processes. Free radicals are denoted by a superscript dot to the right.

Examples: H^., Cl^., HO^., H3C^.

Long-lived free radicals are sub-divided into three categories: stable radicals, persistent radicals, and di-radicals.

Stable radicals: The major example for a stable radical is molecular oxygen O₂. Organic radicals containing conjugated π system can be long lived.

Persistent radicals: They are long lived due to the steric crowding around the radical center and make them physically difficult to react with another molecule.

Di-radicals: Some molecules have two radical centers, they are called di-radicals. Molecular oxygen naturally (atmospheric oxygen) exists as a diradical.

What is an Ion?

Ions are formed when electrons are gained or lost in chemical reactions; they have a positive (+) or negative (-) charge. Those get a negative charge by accepting an electron(s) and positive charge by donating electrons for an electron deficiency molecule or an element. Accepting or donating electrons directly affect the size of the ion; it changes the molecular size dramatically. An atom or a group of atoms without a negative or positive charge is called neutral; to become a neutral atom or a molecule, the number of protons needs to be the same as number of electrons.

Cations (+) ions – often metals since metals lose electrons to become positive (+) charged (Na⁺, Ba²⁺, Ca²⁺, Al³⁺)

Anions (-) ions – often nonmetals since nonmetals gain electrons to become negative (-) charged (Cl^-, S^2-, O^2-, Br^-)

Polyatomic ions - units of atoms behaving as one entity (ClO₃^-, SO₄^2-, PO₄^3-)

Ionic solids – Electrostatic forces hold ions together. Strong ∴ ions held close together ∴ solids.

Cations and anions

What is the difference between Free Radical and Ion?

• Free radicals have one or more unpaired electron, but ions have paired electrons.

• Free radicals are very unstable while ions are relatively stable.

• Free radicals become stable by accepting electrons. Ions are stable when they form complexes with oppositely charged compounds.

• Radicals can exist by themselves, but most of the ions are combined with oppositely charged ions.

• Some ions can act as both oxidizing and reducing agents, but free radicals are neither oxidants nor reducing agents.

• Ions always hold a charge, but free radicals are not charged species even if they have unpaired electrons.

• In an ion, the total number of electrons is always not equal to the number of protons in the nucleus. In a free radical, the number of electrons is equal to the number of protons.

Summary:

Free Radical vs Ion

Free radicals and ions are both described using number of electrons belongs to a particular species. The most significant difference between free radicals and ions is that free radicals have unpaired electrons and ions have paired electrons. Free radicals are more reactive. Ions become chemically stable by forming compounds with oppositely charged ions / molecules.

Images Courtesy:

1. Free radical by Healthvalue (CC BY-SA 3.0)
2. cations and anions by Jkwchui (CC BY-SA 3.0)