Density order of S Block Elements

 Density Order of S-BLOCK Elements 

Density is a ratio of mass and volume of a substance.

Formula :- Density = Mass/Volume 

If mass increase, density increase and if volume increase, density decreases and vice versa.

Now let's look at the S Block Elements

First we discuss about Alkali metal which belongs to Ist A group or 1st Group.

Li, Na, K, Rb, Cs, Fr 

On moving down the group, no of electrons increase, and atomic number also increase it means atomic mass increase, 

Due to increase in mass density will also increases, 

But here is a twist 

On moving down the group and we look at Na & K, Na belongs to 2nd period and K belongs to 3rd period, in Na there is no empty d orbital but in K there is 5 empty d orbitals are present due to this volume increase more as compared to mass, and hence Density decreases

So the correct order is :- 

Li<K<Na<Rb<Cs 

And also the order of density for Alkali earth metal is :- 

Be,Mg,Ca,Sr,Ba,Ra

Correct order is:- 

Ca<Mg<Be<Sr<Ba