Fluorine is the most reactive and electronegative element, appearing as a pale yellow gas at room temperature. It forms compounds with almost all other elements and is highly corrosive.
Fluorine has the highest electronegativity on the Pauling scale and a very small atomic radius. Its valence shell (2p) is close to the nucleus and strongly attracts electrons. Also, the F–F bond, though short, is relatively weak due to electron–electron repulsions between lone pairs, so \(\mathrm{F_2}\) can be readily cleaved to form highly stable \(\mathrm{F^-}\).
The ground-state configuration is \([He]2s^2\,2p^5\). In compounds, fluorine almost exclusively exhibits the oxidation state \(-1\) (as \(\mathrm{F^-}\)), since it is more electronegative than all other elements, including oxygen.
Fluorine is obtained by the electrolysis of anhydrous hydrogen fluoride with dissolved \(\mathrm{KF}\) (to increase conductivity), in a cell with graphite electrodes:
\(\mathrm{2\,HF(l) \xrightarrow{electrolysis} H_2(g) + F_2(g)}\)
Strictly water-free conditions and corrosion-resistant materials are essential due to fluorine’s extreme reactivity.
Weak acid in water: HF is only partially ionized due to strong H–F bonding and extensive hydrogen bonding in solution, so its \(K_a\) is smaller than for HCl/HBr/HI.
Highly dangerous: HF penetrates skin, binds \(\mathrm{Ca^{2+}}\) and \(\mathrm{Mg^{2+}}\), and can cause deep tissue damage and hypocalcemia. Specialized calcium gluconate treatment is required for exposure.
Glass contains silica (\(\mathrm{SiO_2}\)). HF reacts to form volatile silicon tetrafluoride and water (or hexafluorosilicic acid in aqueous media):
\(\mathrm{SiO_2(s) + 4\,HF(aq) \rightarrow SiF_4(g) + 2\,H_2O(l)}\)
Because \(\mathrm{SiF_4}\) is gaseous, the surface is removed, producing an etched finish.
Fluorine forms numerous interhalogens such as \(\mathrm{ClF}\), \(\mathrm{ClF_3}\), \(\mathrm{BrF_5}\), and \(\mathrm{IF_7}\), where fluorine stabilizes high oxidation states on the central halogen.
It also forms oxygen fluorides (\(\mathrm{OF_2}\), \(\mathrm{O_2F_2}\)). In \(\mathrm{OF_2}\), oxygen is formally positive (\(+2\)) since fluorine is more electronegative.
Yes. Fluorine is such a strong oxidizer that it can oxidize water, releasing \(\mathrm{O_2}\) (and often \(\mathrm{O_3}\)) and forming HF:
\(\mathrm{2\,F_2 + 2\,H_2O \rightarrow 4\,HF + O_2}\)
It also forms oxygen fluorides like \(\mathrm{OF_2}\) via direct reaction with oxygen under suitable conditions.
Fluoride can replace hydroxide in hydroxyapatite to form more acid-resistant fluorapatite:
\(\mathrm{Ca_5(PO_4)_3OH + F^- \rightarrow Ca_5(PO_4)_3F + OH^-}\)
This reduces demineralization and enhances remineralization, helping prevent dental caries when used at controlled levels.
Use compatible materials (e.g., nickel, Monel, PTFE), dry systems, and rigorous ventilation. For HF, wear acid-resistant gloves, face/eye protection, and have calcium gluconate gel available. Avoid contact with glass for HF solutions and never confine fluorine without proper pressure-rated equipment.