The arrangement of elements in the long form of periodic table is a perfect matching of electronic configuration of the elements on one hand and physical and chemical properties of the elements on the other.
The elements possessing identical outer electronic configuration should possess similar physical and chemical properties and therefore they should be placed together for an easy and systematic study.
There are 18 vertical columns called Groups. They are numbered from 1 to 18. Every group has a unique configuration.
There are seven horizontal rows. These rows are called Periods.
There are a total of 114 elements known. Of all the known elements, 90 are naturally occurring and others are made through nuclear transformations or are synthesized artificially.
First period consists of only two elements (very short period). Second and third periods consists of only eight elements each (short periods). Fourth and fifth periods consist of 18 elements each (long periods). Sixth period consists of 32 elements (long period). Seventh period is yet incomplete and more and more elements are likely to be added as the scientific research advances.
There are also nick names given to the groups or a cluster of groups on the basis of the similarity of their properties.
Elements with atomic numbers 58 to 71 are called Lanthanoids or Inner Transition elements (First series). Elements from atomic numbers 90 to 103 are called Actinoids or Inner Transition elements (Second series). All elements except transition and inner transition elements are also collectively called Main Group Elements.