Estimate the fraction of molecular volume to the actual volume occupied by oxygen gas at STP. Take the diameter of an oxygen molecule to be 3 Å.
Diameter (size) of oxygen molecule =3A˚ Radius of oxygen molecule, r=23A˚=1.5×10−10m Therefore, volume of 1 mole of oxygen gas at S.T.P =34πr3×N =34×π×(1.5×10−10)3×6.0225×1023 =8.514×10−6m3=8.514×10−3 litre Fraction of the molecular volume occupied =22.48.514×10−3=3.8×10−4