Pariod numbers: periodicity
The period number is an identifier used to describe the row of the standard periodic table in which the element appears.
The lanthanoids and actinoids are extensions of Periods 6 and 7 respectively, hence their assignment to those Periods.
- International Union of Pure & Applied Chemistry: Commission on the Nomeclature of Inorganic Chemistry, Nomenclature of Inorganic Chemistry Recommendations 1990, Ed. G.J. Leigh, Blackwell Science, Oxford, 1990.
- W.C. Fernelius, and W.H. Powell, "Confusion in the periodic table of the elements", J. Chem. Ed., 1982, 59, 504-508.
- Periodic table in any volume of the Inorganic Oxford Chemistry Primers, Oxford University Press, Oxford, UK.