Question

The modern periodic table has been evolved through the early attempts of Dobereiner, Newland and Mendeleev. List one advantage and one limitation of all the three attempts.

Answer 1

Hint: Dobereiner’s triads involved the idea of the relationship between the atomic masses of the elements with their properties.
Newland’s law of octaves involved the arrangement of elements in the increasing order of their atomic masses.
According to Mendeleev’s law, the physical and the chemical properties of elements are periodic functions of their atomic weights.

-Complete step by step answer:
Dobereiner grouped the elements in triads. The elements of each of the triads resembled one another in properties. The atomic mass of the middle element of a triad was found to be the mean of the other two elements in the triad. For example, lithium, sodium and potassium form one triad. Chlorine, bromine and iodine form another triad and so on. Thus, the average mean of lithium and potassium is equal to the atomic mass of the middle element sodium.
-One advantage of the Dobereiner’s triads is that it was the first time that elements were arranged in a sequential manner and one limitation is that it was not applicable for all the elements.
-Newland found out that similar elements are repeated at the eighth place just like the eighth note of an octave of music (Sa, re, ga, ma, pa, da, ni, sa, i.e., atomic number 1 is repeated as sa at number 8). According to this data, lithium, sodium and potassium resemble one another and beryllium, magnesium and calcium resemble one another and so on.
-One advantage of Newland’s law of octaves is that it made the study of the elements comparative and easy and one limitation is that it was only applicable for elements that were discovered at that time and it failed after the discovery of noble gases.
-Mendeleev arranged all the elements known at his time in vertical columns and horizontal rows in the order of their increasing atomic weights. The elements with similar properties were placed beneath each other. He left certain gaps in his table and predicted that newly discovered elements would fill these gaps.
-One advantage of Mendeleev’s periodic table is that it simplified the study of elements and their compounds. Instead of studying the properties of all the elements only the study of the general properties of each group is required.
-One limitation of Mendeleev’s periodic table is that the position of hydrogen is not clear. It resembles the alkali metals as well as the halogens and so it may be placed in the first or seventh group.

Note:
In order to explain all these drawbacks, the modern periodic law modified the previous law.
-According to this law, the physical and the chemical properties of elements are periodic functions of their atomic numbers.
-The long form of the periodic table is based on the modern periodic law.
-According to this form of periodic table, all the elements are arranged in the increasing order of their atomic number.
-The periodic table consists of seven horizontal rows called periods and eighteen vertical columns called groups.