sentences:  Solving for formula_1 we obtain
  
  The radius can also be calculated as
  where formula_11 is molar mass, formula_12 is amount of free electrons per atom, formula_13 is mass density, and
  formula_14 is the Avogadro number.This parameter is normally reported in atomic units, i.e., in units of the Bohr radius.Values of formula_1 for the first group metals