The physical and chemical properties of element are a
periodic function of their atomic masses.
The tabular arrangement of the element based on the
periodic law is called Mendeleev’s Periodic Table.
FEATURES OF MENDELEEV’S PERIODIC TABLE:-
The horizontal rows in the periodic table are called as
periods.
Periods are seven in numbers.
These are numbered from 1 to 7.
Properties of element in a particular period show regular
gradation from left to right.
Vertical column in the periodic table are called group.
There are eight groups numbered from I to VIII.
Groups I to VII are further divided into A and B subgroups.
MERITS OF MENDELEEV’S PERIODIC TABLE:
1
st successful classified all known elements.
He kept some blank places in his periodic table for new
elements that were yet to be discovered.
He predicted properties of these elements even before
they were discovered. Later they were found to be correct.
When noble gases were discovered later. They placed in
periodic table without distributing table
DEMERITS OF MENDELEEV’S PERIODIC TABLE:-
No fixed position for Hydrogen in the periodic table. Hydrogen
resembles alkali as well as halogens.
Isotopes are similar elements have different atomic masses.
They are placed in different position.
Isotopes are chemically similar, they had same position.
Element of higher atomic masses has been placed before an
lower atomic mass. E.g. cobalt (Co=58.93) is placed before
nickel (Ni = 58.71).
Some elements placed in the same sub group had different
properties. E.g. Manganese is placed with halogens which
totally differ in the properties.