Topic 9: Halogens

Halogens - Group VII Elements

Overview of Halogens

  • Positioned in Group VII on the right-hand side of the Periodic Table.

  • Comprise diatomic non-metals:

    • Fluorine (F)

    • Chlorine (Cl)

    • Bromine (Br)

    • Iodine (I)

    • Astatine (At) (radioactive)

General Physical Properties

  1. Physical States and Colors at Room Temperature (RTP):

    • Fluorine (F₂): Gas, Pale yellow-green

    • Chlorine (Cl₂): Gas, Yellowish green

    • Bromine (Br₂): Liquid, Red-brown

    • Iodine (I₂): Solid, Grey-black (also purple gas)

    • Astatine (At₂): Solid, Black

  2. Conductivity:

    • Poor conductors of heat and electricity (lack free ions/electrons).

  3. Solubility:

    • Low solubility in water.

  4. Toxicity:

    • All halogens are toxic.

Trends in Halogens

  • As you move down the group:

    • Density: Increases

    • Reactivity: Decreases

Testing for Chlorine Gas

  • Procedure:

    • Approach damp litmus paper.

  • Observations:

    • Blue litmus turns red then bleaches.

    • Red litmus bleaches.

Test for Halide Ions

  • Procedure:

    • Add a few drops of silver nitrate (AgNO₃) acidified with nitric acid to the aqueous solution.

  • Observations:

    • Chloride (Cl⁻): White precipitate of silver chloride (AgCl) formed, darkens with light.

    • Reaction:
      Ag^+(aq) + Cl^-(aq)
      ightarrow AgCl(s)

    • Bromide (Br⁻): Creamy precipitate of silver bromide (AgBr) formed, darkens with light.

    • Reaction:
      Ag^+(aq) + Br^-(aq)
      ightarrow AgBr(s)

    • Iodide (I⁻): Yellow precipitate of silver iodide (AgI) formed, darkens with light.

    • Reaction:
      Ag^+(aq) + I^-(aq)
      ightarrow AgI(s)

Reactivity of Halogens

  • Fluorine is the most reactive halogen and most reactive non-metal.

  • Reactivity decreases moving down the group.

Displacement Reactions of Halogens

  • General Equation:
    X2(aq) + 2Y^-(aq) ightarrow 2X^-(aq) + Y2(aq)

    • Where:

    • $X$: Halogen displacing another halogen

    • $Y$: Halogen being displaced

  • Examples:

    • Cl2(g) + 2NaBr(aq) ightarrow 2NaCl(aq) + Br2(aq) (Colorless to orange due to Br₂ formation)

    • Cl2(g) + 2NaI(aq) ightarrow 2NaCl(aq) + I2(aq) (Colorless to dark reddish-brown due to I₂ formation)

    • Br2(l) + 2NaI(aq) ightarrow 2NaBr(aq) + I2(aq) (Colorless to dark reddish-brown due to I₂ formation)

Predicting Reactivity

  • Use Trends in Reactivity:

    • Cl2 + 2KI ightarrow I2 + 2KCl

    • I2 + 2KF ightarrow F2 + 2KI

    • Br2 + 2KCl ightarrow Cl2 + 2KBr

Colors in Cyclohexane

  • Observe Colors of Solutions:

    • Bromine solution: [Color specific]

    • Iodine solution: [Color specific]