Periodic Classification of Elements


(a) What was the basis of Mandelẽev’s classification of elements?

(b) List two achievements of Mandelẽev’s periodic tables.

(c) List any two observations which posed a challenge to Mandelẽev’s periodic law.


Write the number of periods and groups in the Modern Periodic Table. How does the metallic character of elements vary on moving (i) from left to right in a period, and (ii) down a group? Give reason to justify your answer.


Na, Mg and Al are the elements of the 3rd period of the Modern Periodic Table having group number 1, 2 and 13 respectively. Which one of these elements has the (a) highest valency, (b) largest atomic radius, and (c) maximum chemical reactivity? Justify your answer stating the reason for each.


An element "X" has mass number 35 and the number of neutrons is 18. Identify the group number and period of "X".


Differentiate between the arrangement of elements in Mendeleev’s periodic table and Modern periodic table.


Explain giving justification the trends in the following properties of elements, on moving from left to right in a period, in the Modern periodic Table.

  1. Variation of valency.
  2. Change of atomic radius.
  3. Metallic to non-metallic character.
  4. Electronegative character.
  5. Nature of oxides.

(a) 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.

(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 Modern periodic law.