Halogens: Physical States, Redox Trends, and Displacement Reactions

Introduction to Halogens

Halogens are elements found in Group 17 of the periodic table. They include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). These elements are known for their distinct physical states and strong redox properties.

Physical States of Halogens

• Fluorine (F): Pale yellow gas
• Chlorine (Cl): Greenish-yellow gas
• Bromine (Br): Reddish-brown liquid
• Iodine (I): Dark purple solid
• Astatine (At): Rare, radioactive solid

Redox Trends of Halogens

Halogens are highly reactive and readily participate in redox reactions. They are excellent oxidizing agents because they have a strong tendency to gain electrons and form negative ions.

• Oxidizing Power: Decreases down the group. Fluorine is the strongest oxidizing agent, while iodine is the weakest.
• Reactivity: Decreases down the group. Fluorine is the most reactive, while iodine is the least reactive.

Change in Oxidation States

In redox reactions, halogens typically change their oxidation state from 0 to -1 as they gain an electron. For example:

• Chlorine: $$\text{Cl}_2 + 2e^- \rightarrow 2\text{Cl}^-$$

Displacement Reactions

Halogens can displace less reactive halogens from their compounds. This is known as a displacement reaction. The more reactive halogen will take the place of the less reactive one.

Example of Displacement Reaction

When chlorine gas is bubbled through a solution of potassium bromide, chlorine displaces bromine:

• $$\text{Cl}_2 + 2\text{KBr} \rightarrow 2\text{KCl} + \text{Br}_2$$