# Q 2.27: Estimate the average mass density of a sodium atom assuming its size to be about 2.5 Å. (Use the known values of Avogadro’s number and the atomic mass of sodium). Compare it with the mass density of sodium in its crystalline phase : . Are the two densities of the same order of magnitude? If so, why?

Estimate the average mass density of a sodium atom assuming its size to be about 2.5 Å. (Use the known values of Avogadro’s number and the atomic mass of sodium). Compare it with the mass density of sodium in its crystalline phase: Are the two densities of the same order of magnitude? If so, why? Given, Diameter of sodium = 2.5

Now, Volume occupied by each atom

We know, One mole of sodium has  atoms and has a mass of

Mass of each Sodium atom

Density  = Mass/ Volume

But, the mass density of sodium in its crystalline phase =

The densities are almost of the same order. In the solid phase, atoms are tightly packed and thus interatomic space is very small.

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