The Chemical Properties of the Halogen Elements & the Hydrogen Halides (Cambridge (CIE) A Level Chemistry): Flashcards

Going down Group 17, the atomic radius increases, so the outer shells are further from the nucleus. An incoming electron experiences greater shielding from the nuclear charge. The halogen's ability to attract (accept) electrons — its oxidising power — therefore decreases.

False.

Chlorine is more reactive than bromine, not the other way around. A more reactive halogen can displace a less reactive one. Bromine cannot displace chloride ions because Cl₂ is the stronger oxidising agent.

Cl₂ (aq) displaces Br^- (aq) ions in solution because chlorine is a stronger oxidising agent. The products are Cl^- ions and Br₂ (aq).

A hydrogen halide is a compound formed by the reaction of a halogen with hydrogen gas (e.g. HF, HCl, HBr, HI). They are all polar covalent molecules that dissolve in water to form acidic solutions.

H₂ + F₂: explosive, even in cool/dark conditions. H₂ + Cl₂: explosive in sunlight. H₂ + Br₂: reacts slowly on heating. H₂ + I₂: forms an equilibrium mixture on heating (reversible reaction).

True.

HF has a short, strong H–F bond (fluorine is small), giving it high thermal stability. HI has a longer, weaker H–I bond due to iodine's larger atomic radius, so it is far less thermally stable.

The thermal stability of hydrogen halides decreases going down Group 17 because the H–X bond becomes weaker as the halogen atom gets larger.

Cl₂ (aq) + 2Br^- (aq) → 2Cl^- (aq) + Br₂ (aq)

Chlorine is the oxidising agent (it gains electrons); bromide ions are oxidised to bromine.

Iodine has a much larger atomic radius than chlorine. The H–I bond is longer and therefore weaker than the H–Cl bond. Less energy is needed to break H–I, so HI decomposes more easily on heating and has lower thermal stability.