Mendeleev’s Periodic Table
In
Mendeleev’s Periodic Table, Mendeleev classify elements according to their
atomic masses and arranged these elements in table according to their
increasing order of atomic masses.
Mendeleev’s Periodic Law
According
to Mendeleev’s Periodic Law – “Physical and chemical properties of elements are
periodic function of their atomic masses”.
Mendeleev’s Periodic Table contains
seven horizontal rows known as periods and nine vertical columns known as
groups.
Groups of Mendeleev’s Periodic Table
1.
In
original Mendeleev’s Periodic Table only 8 groups present because Zero group
contains noble gases is added later after discovery of noble gases.
2.
So,
total vertical column is 9 including group 1 to 8 and Zero group.
3.
Group
1 to 7 are divided into two subgroups (A and B) each.
4.
In
eighth group, three elements found together in each period (from fourth period
onward) known as transition triplet.
Periods of Mendeleev’s Periodic Table
1.
Mendeleev’s
Periodic Table has seven periods.
2.
First
period is known as very short period because contain only two elements.
3.
Second
and Third period is known as short period because contain only 8 elements each.
4.
Fourth
and Fifth period is known as long period because contain 18 elements each.
5.
Sixth
period is known as very long period because contain 32 elements each, 18
elements in table and remaining 14 elements called Lanthanides (from atomic no.
58 to 71)
6.
Seventh
period is known as incomplete period because it contains only 24 elements and
some places are left vacant for elements as they are not known yet. 10 elements
in the table and remaining 14 elements called Actinides (from atomic no. 90 to
103) placed outside at bottom of periodic table.
Demerits of Mendeleev’s Periodic Table
These below
points are some Demerits of Mendeleev’s Periodic Table
1.
Position
of Hydrogen: Hydrogen is placed in 1st as well as in 7th
group because its properties are similar to both groups, which is not explained
well.
2.
Elements
which have similar properties are placed apart in different groups.
Example: Copper
and Mercury with similar properties placed in group first and second.
3.
Elements
with different properties are placed in one group.
Example: Coin
metals like Li, Na, K, Rb, Cs.
4.
Atomic
weights are not kept in serial order.
Example: Argon
with higher atomic weight 39.948 is placed before potassium, which have lower
atomic weight of 39.102
5.
Position
of isotope is not proper because all isotopes of elements are placed in one
group though the atomic weights of isotopes are different.
6.
Eighth group elements position is not
appropriate because elements put in triplet form.
7.
Rare
earth elements (Lanthanides and Actinides) position is not proper so they placed
outside at bottom of periodic table.