. Given below are some elements of the modem periodic table. Atomic number of the element is given in the parentheses

A(4), B(9), C(14), 0(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 reason/for  your answer.

(c) Which two elements amongst these belong to the same period ? Which one of the two has bigger atomic radius?


Best Answer

Ans. (a) D has 1 electron in the outermost shell Atomic no. = 19, Elec. Configuration = 2, 8, 8, 1

(b) A and E belong to the same   group;.i.e 2nd group of the  periodic  table as both have same number  of valence electrons  (i.e.2) in their  outermost shell.

(c) A & B and D & E belong to the same period as they have the same no. of valence shells.

A and B have 2 shells thus belong to 2ndlf'eriod of the periodic table.

D and E have 4 shells thus belong to 4th period of the periodic table.    

A has the bigger atomic radius among A and B and D has the bigger. atomic radius among  D and E as atomic size decreases  on  moving from left to right in a period  (or atomic size decreases  as the atomic number  increases in a period).        

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