Atto

{
  "id": "MLC-T-CHM-000934",
  "term": "Atto",
  "field": "Chemistry",
  "definition": "The standard SI prefix for a factor of one quintillionth, or 10⁻¹⁸. It is assigned the symbol 'a' and is appended to a unit of measure to denote this very small fraction of the base unit. For example, an attosecond (as) is 10⁻¹⁸ seconds, a timescale relevant to the motion of electrons in atoms, and the mass of a single protein molecule can be measured in attograms (ag).",
  "subject": "Physical and Biophysical Chemistry",
  "references": [
    "Green Book, 2nd ed., p. 74 (https://goldbook.iupac.org/files/pdf/green_book_2ed.pdf)"
  ],
  "url": "https://mlchart.com/terminology/chemistry/atto/"
}