Mendeleev published one of the first periodic tables in 1869, arranging the 63 known elements in order of atomic mass with chemically similar elements in the same columns. The periodic table is based on patterns in properties and reactivities between elements. Mendeleev's table included 7 periods and 8 groups, and predicted elements yet to be discovered by leaving gaps. Later work by Moseley established that atomic number determines an element's position and led to the modern periodic table.

3. Dmitri Mendeleev (1869)
In 1869 Mendeleev and LotharMeyer (Germany)
published nearly identical classification schemes for
elements known to date. The periodic table is base on
the similarity of properties and reactivities exhibited by
certain elements. Later, Henri Moseley
( England,1887-1915) established that each elements has
a unique atomic number, which is how the current
periodic table is organized

4. Features of Mendeleev’s periodic
Table
 Mendeleev arranged all the elements at that time (63
elements) in the increasing order of their atomic
masses in such a way that chemically similar elements
were placed in the same vertical column.
 In Mendeleev’s periodic table, the elements were
arranged in 7 horizontal rows (called periods) and
eight vertical columns (called groups).

5. Mendeleev’s periodic law
 Properties of elements depend on their atomic masses
 When elements are arranged according to their atomic
masses, properties are repeated at regular intervals.

6. Merits of Mendeleev’s
Classification
 Mendeleev’s left vacant spaces in the table, this stood
for new elements yet to be discovered.
 He corrected the atomic masses of certain elements.

7. Demerits of Mendeleev’s
classification
 He didn’t give proper place for hydrogen.
 He didn’t give proper place for transition elements.
 He violate the increasing of atomic masses in certain
places.