A Period Group (or Family) is the columns of elements in a periodic table of chemical elements that is numbered from Group 1 to 18. International Union of Pure and Applied Chemistry (IUPAC) recommended names are: Group 1: alkali metals; Group 2: alkaline earth metals; Group 11: coinage metals; Group 15: pentels, pnictogens; Group 16: chalcogens; Group 17: halogens; Group 18: noble gases.
Reference Definition by Wikipedia: In chemistry, a Period Group (also known as a family) is a column of elements in the periodic table of the chemical elements. There are 18 numbered groups in the periodic table, but the f-block columns (between groups 2 and 3) are not numbered. There are three systems of group numbering. The modern numbering group 1 to group 18 is recommended by the International Union of Pure and Applied Chemistry (IUPAC). Two earlier group number systems exist: CAS (Chemical Abstracts Service) and old IUPAC. Both use numerals (Arabic or Roman) and letters A and B. Both systems agree on the numbers.
Related Definitions in the Project: The Engineering; Element and Substance
