Question

Given below are some elements of the modern periodic table : 4Be, 9Fe, 14Si, 19K, 20Ca [3] (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?

Answer 1

Answers
1.K has one electron in outermost shell.
   Its Configuration is 2,8,8,1
2.Be And Ca belong to same group because both of them has 2          electrons in outermost shell that is why they are placed in group      II A
3.Be and Fe belong to same period.Be has greater atomic size        because atomic size decreases along a period
   K And Ca also belong to same period .K has greater atomic Size      beacuse atomic size decreases along a period.

Answer 2

(i).Element K (potassium) has 1 electron in the outermost shell.
E.C.-2,8,8,1
(ii)Element Be (beryllium) and Ca (calcium) belong to same group because both of them are in the second group because their outermost shell has 2 electrons that is their valency is 2. So we keep them in same group.
(iii)Element Fe (iron) and K (potassium) belong to same period that is period 4.
K (potassium) has a greater atomic size because K is at left side of the period and Fe is at right side as compared to K. So as we go from left to right in period, the size of atom decreases as the no. of valence electrons increase.