Given below are some elements of the modern periodic table:
$_{4} B e,_{26} F e,_{14} S i,_{19} K,_{20} C a$
(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?

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Solution

1. $_{19} K$ i.e. potassium has 1 electron in the outermost shell. Its electronic configuration is $2, 8, 8, 1$ .

2. Berylium $(_{4} B e)$ and Calcium $(_{20} C a)$ belong to group 2. They both are alkaline earth metals and contain valency as 2 and hence, placed in group 2.

3. $_{26} F e,_{19} K$ and $_{20} C a$ all belong to the 4th period. Moving left to right across a period, atomic radius usually decreases. Hence, K has the biggest atomic size as compared to $_{20} C a$ and $_{26} F e .$

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