The structural features of the long form the of periodic table are:
1. In this periodic table the elements are arranged in order of their increasing atomic numbers.
2. There are seven periods. The elements in the periods are as follows:
- 1st period contains 2 elements, H(l) and He(2)
- 2nd period contains 8 elements, Li(3) to Ne(10)
- 3rd period contains 8 elements, Na(ll) to Ar(18)
- 4th period contains 18 elements, K(19) to Kr(36)
- 5th period contains 18 elements, Rb(37) to Xe(54)
- 6th period contains 32 elements, Cs(55) to Rn(86)
- 7th period contains 19 elements, starting from Fr(87).
This period is still incomplete.
The second and the third periods containing 8 elements each are called short periods. The fourth and the succeeding periods are the long periods.
3. The table has 18 vertical columns (excluding lanthanides and actinides), but the number of groups is 16 only. This is because group VIII has three vertical columns.
4. In this table, the subgroups of Mendeleev’s periodic table are kept separated. The elements belonging to subgroups A are called normal or representative elements and those belonging to subgroups B are called transition elements. Elements of group IA are called alkali metals, while the elements of group IIA are called alkaline earth metals. Elements of group VIIA are called the halogens and those of group 0 are the noble or inert gases.
5. The two rows at the bottom of the table consist of the lanthanides or lanthanides and the actinides. They belong to group IIIB.
6. In this table, a complete separation of metals and nonmetals has been achieved. The elements left of the staircase line (see the table) are mostly metals while those on the right of it are nonmetals. Some of the elements that lie right next to the staircase line possess properties intermediate between those of metals and nonmetals. These are called metalloids. These are boron, silicon, arsenic, antimony, etc.