Pauling give method to calculate univalent ion radii by assuming that
(i) In ionic crystal (let `M^(+)X^(-))` cations and anions are is contact of eac other and sum of their radii is equal to interionic distance, i.e.,
`d_((M^(+)-X^(-)) = r_(M^(+) +r_(X^(-))`
(ii) The radius of an ion having noble gas configuration is inversely proportional to the effective nuclear charge felt at the periphery of the ion, i.e., `r_((M^(+))) = (C)/(Z_(eff(M^(+))))` and `r_((X^(-))) = (C)/(Z_(eff(X^(-))))`
Here C is constant of proportionality whose value depends on electronic configuration of ion. Thus,
`d_((M^(+)-X^(-))) =(C)/(Z_(eff(M^(+)))) +(C)/(Z_(eff(X^(-))))` pm
`Z_(eff)` is the effective nuclear charge whose value can be calculated by the formula: `Z_(eff) = Z - sigma`. Here `sigma` is shielding constant and for neon, the value of `sigma` when calculate by Slater's rule is found to be 4.5
The value of univalent radii for `F^(-)` as calculated by Pauling method is (given that interionic distance of `NaF = 231`pm):