Structural features of long form of periodic table :
The form of periodic table consists of horizontal rows and vertical columns. Horizontal row is termed as period while vertical column is called group.
Periods : The long form of the periodic table consists of total seven periods. These are numbered as 1,2,3,4,5,6 and 7. The first period contains only two elements while seconds and third periods contain eight elements each. These periods are referred as short periods and contain , and 18,18 and 32 elements respectively. The fourteen lanthanoids placed in series at the bottom of the periodic table are supposed to be present in the sixth period.The seventh period is till incomplete and contains 23 elements including 14 members of the actinoid series placed at the bottom of the periodic table.
Groups : In all there are 18 groups ( vertical columns ) in the long form of the periodic table. Earlier, these groups were designated as IA, IB, IIA, IIB,...... VIII and 0 groups. According to the new recommendiations of the International Union of Pure and Applied Chemistry ( IUPAC ) the groups are numbered from 1 to 18.
* Elements of groups 1,2 and 13 to 17, acoording to IUPAC recommendation, are called normal or representative elements.
* Elements form group 3 to 12 are called transition elements.
* Noble gases or Inert gas elements are placed in group 18.
* Two series of fourteen elements each, called Lanthanoids and Actinoids are placed at the bottom of the periodic table.
* Lanthanoids are placed in the 3rd group and sixth period.
* Actinoids are placed in the 3rd group but in the seventh period.
* Lanthanoids and Actonoids are also called as inner transition elements or rare earth elements.