(a) The modem 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.' (b) Name the scientist who first of all showed that atomic number of an element is a more fundamental property than its atomic mass. (c) State Modem Periodic Law.

(a) The modem Periodic Table has been evolved through the early attemp

1.	(a) The modem 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.' (b) Name the scientist who first of all showed that atomic number of an element is a more fundamental property than its atomic mass. (c) State Modem Periodic Law.
Answer» Solution :(a) Dobereiner Attempt : ADVANTAGE : The atomic mass of the middle element of the triad was the mean of the other two elements. Limitation : Dobereiner could identify only three TRIADS. Newland Attempt : Advantage : Every eighth element has properties similar to that of the first. Sodium is the eighth element after lithium. These two elements have similar properties. Limitation : Newlands law of Octaves was found to be applicable only upto calcium. After calcium, every eight element did not possess properties similar to that of the first. Mendeleev Attempt : Advantage : The elements were arranged on the basis of their fundamental property, the atomic mass and also on the similarity of CHEMICAL properties. Limitation : No FIXED position in the periodic table could be given to hydrogen by Mendeleev classification. (b) Henry MOSELEY. (c) Properties of elements are a periodic function of their atomic number.