Hydrogen Halides

Thermal stability: HF > HCl > HBr > HI (H–I easiest to break) Acid strength in water: HF < HCl < HBr < HI HF is weak because H–F is very strong (hard to ionise) — not because “F is most electronegative so HF is strongest acid”. Keep the two lists separate.

HX means HF, HCl, HBr, HI. Heat stability: HF strongest molecule, HI weakest bond to break. As acids in water: HF weak; HCl, HBr, HI strong — and strength rises toward HI.

Always label which trend you mean. Thermal stability ≠ acid strength. Quote HF < HCl < HBr < HI for acidity and explain HF via strong H–F bond. Mention H-bonding in HF as supporting context if asked, without claiming electronegativity makes HF the strongest acid.

Acid strength here is about ease of producing H₃O⁺ / H⁺ in water. A very strong H–F bond raises the barrier to dissociation despite fluorine’s electronegativity. Reducing power of HX / X⁻ also rises down the group (HI / I⁻), which is a related but separate exam thread.

Stability HF>…>HI · Acid strength HF<HCl<HBr<HI · HF weak ← strong H–F · do not say “most EN ⇒ strongest acid”.