Acidity Ranking

Compare molecules side-by-side to determine which is more acidic and why.

Hydrogen Fluoride vs Hydrogen Chloride

pKa 3.2 vs -7

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The Two Molecules

Both HF and HCl are hydrogen halides - a hydrogen bonded to a halogen. Which one gives up its proton more easily?

5 Factors That Affect Acidity

1. Atom size - larger atoms stabilize charge better

2. Electronegativity - more EN atoms hold electrons tighter

3. Resonance - delocalization stabilizes the conjugate base

4. Induction - electron-withdrawing groups pull density away

5. Hybridization - more s-character = tighter electron hold

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About This Pair

Hydrogen Fluoride vs Hydrogen Chloride

HCl is a much stronger acid than HF because Cl is larger than F. The larger Cl- anion stabilizes the negative charge over a bigger volume, making it a weaker base and HCl a stronger acid.

Atom Sizebeginner

Acidity Factors

Atom Size - Larger atoms stabilize negative charge (down a group)
Electronegativity - More EN atoms hold bonding electrons tighter (across a period)
Resonance - Delocalization spreads charge over multiple atoms
Inductive Effect - EWGs pull electron density through sigma bonds
Hybridization - More s-character holds electrons closer to nucleus