Question

₁₉K, ₃Li, ₁₁Na, ₄Be Which of these atoms has smallest atomic radius? Write down the electronic configuration of the elements from the given atomic numbers. Answer the question with explanation

Answer 1

The smallest atomic radius among of these (₁₉K, ₃Li, ₁₁Na, ₄Be ) atoms are Beryllium (₄Be ) 

Before discussing why ? First we must know what is Atomic radius ?

Atomic radius :- Atomic radius is known as the distance from the centre of the nucleus across the surrounding electrons.

The correct order of these atoms ⇒ { K > Na > Li > Be }

Reason/ Explanation :- 

(i) On moving down the group the atomic size increase, due to electrons are added in the new shells. 
(ii) On moving in a group from top to bottom then Atomic radius increases. 

$Atomic Radius \alpha \frac{1}{Electron Affinity}$

Hence the correct order will be like - { K > Na > Li > Be} .


Electronic configuration :-

Lithium (Li³)     ---→ 1s²,2s¹

Beryllium (Be⁴)---→1s²,2s²

Sodium(Na¹¹)-----→1s²,2s²,p⁶,3s¹

Potassium (K¹⁹)--→1s²,2s²,2p⁶,3s²,3p⁶,4s¹ 




Hope it Helps :-)