soft acid

chemistry

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July 13, 2026

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In chemistry, a "soft acid" is a classification within the Lewis acid framework. Lewis acids are electron acceptors. Soft acids, as opposed to "hard acids," are characterized by their atomic structures being more readily deformable.1

Soft acids tend to react preferentially with soft bases, which share this characteristic of being more deformable. Examples of soft acids include cuprous, silver, and mercurous cations, as well as halogen cations. This concept helps predict the outcome of certain chemical reactions based on the nature of the interacting species.1

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acid–base reaction
Lewis acids
…with hard bases and, similarly, soft acids react with soft bases. The terms hard and soft are chosen to suggest that the atomic structures associated with hard acids and bases are rigid and impenetrable, whereas those associated with soft acids and bases are more readily deformable. Hard acids include the…
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…with hard bases and, similarly, soft acids react with soft bases. The terms hard and soft are chosen to suggest that the atomic structures associated with hard acids and bases are rigid and impenetrable, whereas those associated with soft acids and bases are more readily deformable. Hard acids include the…
Read More