Definition

The name is derived from Greek: "halous" (salt) + "gen" (former). Halogens are reactive non-metals existing as diatomic molecules.

• Elements: Fluorine, Chlorine, Bromine, Iodine, Astatine, Tennessine
• Reactive non-metals

Appearance

• Fluorine (F₂): Pale yellow gas
• Chlorine (Cl₂): Yellow-green gas
• Bromine (Br₂): Red-brown liquid
• Iodine (I₂): Grey-black solid, dark purple vapors when warmed

Electronic Configuration

General: ns²np⁵ (7 valence electrons). Halogens tend to gain one electron to form univalent negative ions (F⁻, Cl⁻, Br⁻, I⁻).

Density

• Fluorine: 0.0017 g/cm³
• Chlorine: 0.0032 g/cm³
• Bromine: 3.1028 g/cm³
• Iodine: 4.933 g/cm³

Reactivity

Reactivity decreases down the group as electronegativity decreases. Order of decreasing reactivity: F₂ ≥ Cl₂ ≥ Br₂ ≥ I₂.

Displacement Reactions

More reactive halogens can displace less reactive ones from their compounds:

• Br₂ + 2KI → 2KBr + I₂
• Cl₂ + 2KBr → 2KCl + Br₂
• Cl₂ + 2NaI → 2NaCl + I₂