Chapter 5: The Halogen and The Noble Gases

Includes Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), Astatine (At). 'Halogen' means salt-former.

• General Trends: ns²np⁵ configuration. F, Cl (Gases), Br (Liquid), I (Solid). Oxidizing power decreases down the group (F2 > Cl2 > Br2 > I2).
• Peculiar Behaviour of Fluorine: Small size, high electronegativity, low dissociation energy of F2 bond. Forms only -1 oxidation state.

Properties of HF, HCl, HBr, HI.

• Acid Strength: HF < HCl < HBr < HI. HI is strongest because bond strength decreases down the group.
• Bond Energy: H-F > H-Cl > H-Br > H-I.
• Unique Properties of HF: Liquid due to strong Hydrogen Bonding. Weak acid. Etches glass (forms H2SiF6). solvent.

Oxides

• OF2: Oxygen difluoride.
• ClO2: Chlorine dioxide. Paramagnetic, exploded by heat. Used as bleaching agent.
• I2O5: Iodine pentoxide. Used for quantitative estimation of CO.

Oxyacids

Hypohalous (HXO), Halous (HXO2), Halic (HXO3), Perhalic (HXO4).

• Acid Strength: HClO4 > HClO3 > HClO2 > HClO. Increases with oxidation state of halogen.
• Perchloric Acid (HClO4): Strongest acid.

• Preparation: Interaction of Cl2 with dry slaked lime Ca(OH)2.
• Methods: Hasenclever's method (Old), Beckmann's method (Modern).
• Reaction: Ca(OH)2 + Cl2 → CaOCl2 + H2O.
• Available Chlorine: Chlorine set free when bleaching powder reacts with excess acid. Avg 35-40%.
• Uses: Disinfectant, sterilization of water, bleaching cotton/linen.

He, Ne, Ar, Kr, Xe, Rn. ns²np⁶ (except He ns²). Chemically inert.

Compounds of Xenon

• Fluorides: XeF2, XeF4, XeF6. Prepared by direct combination of Xe and F2. Strong fluorinating agents.
• Oxides: XeO3 (Explosive solid), XeO4.
• Oxyfluorides: XeOF4.

Uses

• Helium: Weather balloons, breathing mixture for divers (80% He, 20% O2).
• Neon: Neon signs.
• Argon: Electric bulbs, welding (inert atm).
• Radon: Radiotherapy (Cancer treatment).