What is the Difference Between Hard Acid and Soft Acid?

The Difference Between Hard Acid and Soft Acid can be summarized as follows:

• Hard Acids:
• Cations of electropositive metals.
• Relatively nonpolarizable with a higher charge-to-radius ratio.
• Typically have a high charge density and small ionic size.
• Examples: H+, Li+, Na+, K+, Be2+, Mg2+.
• Soft Acids:
• Cations of less electropositive metals.
• More polarizable with a lower charge-to-radius ratio.
• Typically have a lower charge density and greater ionic size.
• Examples: BF3, Al2Cl6, CO2, SO3.

According to the Hard and Soft Acid-Base (HSAB) Theory, hard acids prefer to bind to hard bases, and soft acids prefer to bind to soft bases. The interactions between hard acids and hard bases are primarily electrostatic, while the interactions between soft acids and soft bases are more covalent in nature.

Comparative Table: Hard Acid vs Soft Acid

Here is a table comparing hard acids and soft acids:

Hard acids have a high charge-to-radius ratio and are relatively nonpolarizable, while soft acids have a low charge-to-radius ratio and are more polarizable. Hard acids are typically cations of electropositive metals, whereas soft acids are cations of less electropositive metals.