text: N-X-L nomenclature, introduced collaboratively by the research groups of Martin, Arduengo, and Kochi in 1980, is often used to classify hypervalent compounds of main group elements, where:
  * N represents the number of valence electrons
  * X is the chemical symbol of the central atom
  * L the number of ligands to the central atom
  Examples of N-X-L nomenclature include: 
  * XeF, 10-Xe-2
  * PCl, 10-P-5
  * SF, 12-S-6
  * IF, 14-I-7