Hard acid

{
  "id": "MLC-T-CHM-013142",
  "term": "Hard acid",
  "field": "Chemistry",
  "definition": "A Lewis acid characterized by a small atomic or ionic radius, a high positive oxidation state, and low polarizability. These species have vacant orbitals of high energy and do not readily distort their electron clouds. Examples of hard acids include H+, Li+, Na+, K+, Mg2+, Ca2+, and Al3+, which preferentially bond with hard bases.",
  "subject": "Organic and Biomolecular Chemistry",
  "see_also": [
    "Lewis acid",
    "hard base",
    "class (a) metal ion",
    "coordination",
    "polarizability"
  ],
  "references": [
    "PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1120 (https://doi.org/10.1351/pac199466051077)"
  ],
  "url": "https://mlchart.com/terminology/chemistry/hard-acid/"
}