Question

4.(a) What is meant by periodicity
in properties of elements with reference to the periodic table?
(b) Why do all the elements of the same group have similar properties?
(c) How will the tendency to gain electrons change as we go from left to right across a period? Why?
5.(a) Which two criteria did Mendeleev use to classify the elements in his Periodic Table?
(b) State Mendeleev’s periodic law.
(c) Why could no fixed position be given to hydrogen in Mendeleev’s Periodic Table?
(i) Sizes of their atoms
(ii) Their metallic characters
(iii) Their valencies in forming oxides
(iv) Molecular formulae of their chlorides​

Answer 1

Answer:

4.a) Element will show certain similarity in their properties after a fixed interval of time.

b) because they have same valency

c) It increases because of increase in electronegativity of element from left to right.

5.a) Atomic mass

b) Physical and chemical properties of an element are the periodic function of their atomic weight.

c) because it show the property of both alkali metals and halogens.