# Origin of the 15% difference limit between solute and solvent atom radii in the Hume-Rothery rules

According to the Hume-Rothery rules for the substitutional solid solutions the atomic sizes of the the solute and solvent must not differ by more than 15%.

Why should it be so?

a) the atomic radii of metal A and metal B do not differ significantly, and thus there are chances both metals blend statistically with each other. Which would be covered by the $$< 15\%$$-rule, a situation similar to mixing apples and oranges in one crate.