The Total solution for NCERT class 6-12
Estimate the average mass density of a sodium atom assuming itssize to be about 2.5. (Use the known values ofAvogadroтАЩs number and the atomic mass of sodium). Compare it with the densityof sodium in its crystalline phase: 970 kg mтАУ3. Are the twodensities of the same order of magnitude? If so, why?
Diameter of sodium atom = Size of sodium atom =2.5┬а
┬а
= 1.25 ├Ч 10тАУ10┬аm
According to the Avogadro hypothesis, one mole of sodium contains6.023 ├Ч 1023┬аatoms and has a mass of 23 g or 23 ├Ч 10тАУ3┬аkg.
It is given that the density of sodium in crystalline phase is 970kg mтАУ3.
Hence, the density of sodium atom and the density of sodium in itscrystalline phase are not in the same order. This is because in solid phase,atoms are closely packed. Thus, the inter-atomic separation is very small inthe crystalline phase.