Question

Titanium, Zirconium and 'Hafnium belong to the same group. The density of Zr is slightly greater than titanium. But the density of Hafnium is double, to that of Zr. Give reason. Given that the IP values of the elements and comment on the observed trend.

Answer 1

X and Y are the starting elements in 3rd and 4th periods

Thus they are $X=Na\Rightarrow$ sodium

$Y=K\Rightarrow$ potassium

Density of potassium is less than sodium Reason:

Density= mass/ volume

Density$\infty$ mass and density $\infty$ 1/volume

Basically in case of potassium, the increase in shell size outweighs the pull of the core on the outermost electron and so potassium is less dense than sodium. When we move from sodium to potassium, effect of the increase in the volume is more pronounced as compared to effect of the increase in the atomic mass.