Main features of mendeleev's Periodic Table:
(a) There are seven horizontal rows in the periodic table. They are called periods and are numbered from 1 to 7.
(b) In a given period, there is regular gradation in the properties of elements from left to right.
(c)
There are eight vertical columns in the periodic table. These are named
as groups. They are numbered from I to VIII. Groups I to VII are
subdivided into subgroups A and B.