In chemistry, a group is a column of elements in the periodic table of the chemical elements. There are 18 numbered groups in the periodic table, and the f-block columns are not numbered. The elements in a group have similar physical or chemical characteristics of the outermost electron shells of their atoms, as most chemical properties are dominated by the orbital location of the outermost electron. There are three systems of group numbering. The modern numbering group 1 to group 18 is recommen