Question

Write Merits and limitations of Mendeleev’s Periodic Table

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Answer 1

Answer:

Merits of Mendeleev's Periodic Table:

⋅ Mendeleev was first to properly arrange and classify all elements and was able to explain the periodicity in their chemical properties.

⋅ Mendeleev left some gaps for undiscovered elements. He predicted that some elements would be discovered in future. He also predicted properties of those undiscovered elements.

Demerits of Mendeleev's Periodic Table:

⋅ Position of hydrogen was not justified.

⋅ Increasing order of atomic mass could not be maintained throughout the table.

⋅ There is no place for isotopes.

Answer 2

Answer:

Merits of Mendeleev's periodic table:

i. Mendeleev was the first to successfully classify all known elements.

ii. Mendeleev's periodic table helped to revise the atomic masses of some

elements so as to give them proper places in the periodic table in accordance

with their properties.

For example, the atomic mass of beryllium (Be) was previously determined to

be 14.09. This value was changed to the correct value of 9.4 and beryllium (Be)

was placed before boron (B).

iii. Mendeleev's periodic table had left some vacant spaces in it. These were for

elements that were yet to be discovered.

Three of these unknown elements were named eka-boron, eka-aluminium and

eka-silicon. He predicted properties of these elements even before they were

discovered.

These elements are scandium (Sc), gallium (Ga) and germanium (Ge)

respectively. The properties of these elements matched well with those

predicted by Mendeleev.

iv. There was no place reserved for noble gases in Mendeleev's original periodic

table. But, when noble gases were discovered later, they were placed in a new

group called as “zero group' in Mendeleev’s periodic table without disturbing

the positions of other elements.