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Questions
Given below are some elements of the modern periodic table. Atomic number of the element is given in parentheses.
A(4), B(9), C(14), D(19), E(20)
(a) Select the element that has one electron in the outermost shell. Also, write the electronic configuration of this element.
(b) Which two elements amongst these belong to the same group? Give reasons for your answer.
(c) Which two elements amongst these belong to the same period? Which one of the two has bigger atomic radius?
Given below are some elements of the modern periodic table: (3)
4Be, 9Fe, 14Si, 19K, 20Ca
(i) Select the element that has one electron in the outermost shell and write its electronic configuration.
(ii) Select two elements that belong to the same group. Give reason for your answer.
(iii) Select two elements that belong to the same period. Which one of the two has bigger atomic size?
Solution
(a) Element D (19) has one electron in its outermost shell. Its electronic configuration is 2, 8, 8, 1.
(b) Elements A (4) and E (20) have two electrons in their outermost shells.
Electronic configuration of A: 2, 2
Electronic configuration of E: 2, 8, 8, 2
Since they both have a valency of two, they belong to group 2 of the periodic table.
(c) Elements A (4) and B (9) belong to the second period, and elements D (19) and E (20) belong to the fourth period of the periodic table.
Since the effective nuclear charge which pulls the outermost electron closer to the nucleus increases from left to right in a period, the atomic radii of the elements decreases. A (4) has a bigger atomic radius than B (9) and D (19) has a bigger atomic radius than E (20).
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