Question

State Mendeleev’s periodic law.

Answer 1

Hint: Mendeleev is best known for his discovery of the periodic law, which he introduced in 1869, and for his formulation of the periodic table of elements. The atomic mass of nickel is less than that of cobalt; in spite of that cobalt is placed before nickel. Groups from 1 to VII are meant for normal elements and group VIII is for transition elements.

Complete step by step answer:
Let us see what Mendeleev’s law actually states!
The law states that “the properties of elements are the periodic function of their atomic masses.”

Now, let us try to understand how he formulated this law!
In 1869, after the rejection of Newlands Octave Law, Mendeleev Periodic law came into picture. In Mendeleev’s periodic table, the elements were arranged on the basis of the fundamental property, atomic mass and chemical properties. After studying the properties of every element, Mendeleev found that the properties of elements were to atomic mass in a periodic manner.
So, here comes the trick now, he arranged the elements in such a way that elements with similar properties fell into the same vertical columns of the periodic table. Whereas for chemical properties, he took 63 cards and on each card and he wrote the properties of one element. He grouped the elements with similar properties and pinned it on the wall. He observed that elements were arranged in the increasing order of atomic mass and there was the periodic occurrence of elements with similar properties.
Therefore, according to this observation, he formulated this periodic law.

Let us go through a few merits and demerits of the Mendeleev Periodic table.
Merits:
Some gaps were left for the elements which were yet to be discovered. So even if a certain element is discovered, it can be placed in a new group without disturbing any existing group.
Demerits:
He was unable to locate hydrogen in the periodic table.
Later on, isotopes of elements were found which violated Mendeleev’s periodic law.

Note: Modern periodic table is considered better than mendeleev’s periodic table because it does correct defects of the Mendeleev’s periodic table. Modern periodic table considers atomic numbers as the fundamental property that decides the properties of the elements.