Covalent radius of fluorine

Bonds to fluorine have considerable ionic character, a result of its small atomic radius and large electronegativity.

[1] Brockway prepared a vapour of F2 molecules by means of the electrolysis of potassium bifluoride (KHF2) in a fluorine generator, which was constructed of Monel metal.

In 1960, Linus Pauling proposed an additional effect called "back bonding" to account for the smaller experimental values compared to the theory.

They determined that there was no significant back-bonding, but instead proposed that there is extra pi bonding, which arose from the donation of ligand lone pairs into X-F orbitals.

In 1992, Ronald Gillespie and Edward A. Robinson suggested that the value of 71 pm was too large because of the unusual weakness of the F-F bond in F2.

In 1997, Gillespie et al. found that his original prediction was too low, and that the covalent radius of fluorine is about 60 pm.

Contour plots of the electron density distribution were then drawn, which were used to evaluate the bond length of fluorine to other molecules.

From this, they discovered that the Schomaker-Stevenson and Pauling assumptions were too high, and their previous guess was too low, thus, resulting in a final value of 60 pm for the covalent bond length of fluorine.