Q9 of 48 Page 1

Given below are some elements of the modern periodic table:

4 Be, 9 Fe, 14 Si, 19 K, 20 Ca


(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?


(i) Since 19 K has 1 electron present in its outermost shell and the configuration will be:


2, 8, 8 1


(ii) Since no. of valence electrons are same in 4 Be and 20 Ca. So, 4 Be and 20 Ca belongs to the same group.


(iii) 19 K and 20 Ca, both have 4 energy shells present. So, 19 K and 20 Ca belongs to the same period.


As we know on moving from left to right in a period, the atomic size decreases. So, 19 K will have larger size than 20 Ca.


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