Children's, Intermediate and Advanced Online English Dictionary & Thesaurus

Word Explorer
Children's Dictionary
Help
Help
Help
Multi-word Results
periodic law the principle that the properties of the chemical elements recur periodically when the elements are arranged in increasing order of their atomic numbers.
periodic system a system of classifying the chemical elements, based on the periodic law.
periodic table a table that illustrates the periodic system of the chemical elements, classified according to atomic number.