Write two major shortcomings of mendeleev's periodic table? how have these been removed in the modern periodic table?
Answers
Two limitations of Mendeleev’s periodic table are:
*The position of the element hydrogen in the periodic table could not be ascertained. This is because hydrogen has the properties of both halogens and alkali.
*Because isotopes have different atomic masses, they should be placed at different points of the periodic table. However, in Mendeleev’s periodic table, this has not been done and the isotopes are placed next to their core element because they share similar properties.
Henry Moseley illustrated that the periodic properties of an element can be explained better by its atomic number rather than its atomic mass. This formed the basis of arranging the elements in the modern periodic tables. Elements are arranged in increasing order of atomic numbers.
The two major short comings of Mendeleev’s periodic table were
(i) It could not justify the position of hydrogen in the periodic table whether in
group 1 or group 8
(ii) It could not assign proper position to the different isotopes of the same element.
The main reason for these short comings was the basis of the Mendeleev’s periodic
table. It regarded atomic masses of the elements as the basis of classification. The
modern periodic table regards atomic numbers of the elements as the basis of
classifying the elements. It removed both the short comings from the table.