Question

(a) What is a group in the periodic table? In which part of a group would you separately expect the elements to have (i) the greatest metallic character (ii) the largest atomic size?
(b) In what respects do the properties of group 1 elements differ from those of group 17 elements? Explain with examples by taking one element from each group.
(c) From the standpoint of atomic structure, what determines which element will be the first and which the last in a period of the periodic table?
(d) Explain why, the properties of elements are repeated after 2, 8, 18 and 32 elements in the periodic table.
(e) What are the advantages of the periodic table?

Answer 1

(a) A group is a vertical column of elements in the periodic table.
In a group:
(i) The greatest metallic character is expected by elements in the lowest part of the group, as the metallic (electropositive) character increases on going down in a group.
(ii) The largest atomic size is found at the bottom of the group, as the atomic size increases on moving down in a group of the periodic table.

(b) Let us explain the properties by taking the example of sodium (Na) in group 1 and chlorine (Cl) in group 17:

Properties	Group 1	Group 17
i) Atomic number	Na, atomic number is 11	Cl, atomic number is 17
ii) Size of the atom	Na has a smaller size than Cl	Cl has a larger atomic size comparatively
iii) Metallic character	Na is a metal, shows more metallic character	Cl is non-metallic
iv) Valence electron	Number of valence electrons is 1 for Na metal	Number of valence electrons is 7 for Cl
v)Electronegativity/ Electropositivity	Na is electropositive in nature	Cl is electronegative in nature
vi) Chemical reactivity	Na is basic in nature	Cl is acidic in nature

(c) The number of valence electrons in atoms determines which element will be the first and which the last in a period of the periodic table.

(d) The electronic configurations are repeated because 2, 8, 18 and 32 are the maximum number of electrons that can be placed in the four atomic shells, namely, K, L, M and N. The properties of the elements are repeated after 2, 8, 18 and 32 because the electronic configurations of elements are repeated after 2, 8, 18 and 32.

(e) Advantages of the periodic table:
(i) The study of elements and its properties is made easy.
(ii) By knowing the position of the element in the periodic table, prediction of the type of compounds that the elements form becomes easy.
(iii) The study of chemistry has been made easy in schools and colleges by using the periodic table chart as a teaching-aid.