Alkali metals form ionic and highly soluble monofluorides; these have the cubic arrangement of sodium chloride and analogous chlorides.
Alkaline earth difluorides possess strong ionic bonds but are insoluble in water, with the exception of beryllium difluoride, which also exhibits some covalent character and has a quartz-like structure.
Rare earth elements and many other metals form mostly ionic trifluorides.

Covalent bonding first comes to prominence in the tetrafluorides: those of zirconium, hafnium and several actinides are ionic with high melting points, while those of titanium, vanadium, and niobium are polymeric, melting or decomposing at no more than 350 °C (660 °F).
Pentafluorides continue this trend with their linear polymers and oligomeric complexes.
Thirteen metal hexafluorides are known, all octahedral, and are mostly volatile solids but for liquid MoF
₆ and ReF
₆, and gaseous WF
₆. Rhenium heptafluoride, the only characterized metal heptafluoride, is a low-melting molecular solid with pentagonal bipyramidal molecular geometry.
Metal fluorides with more fluorine atoms are particularly reactive.
Alkali metals form ionic and highly soluble monofluorides; these have the cubic arrangement of sodium chloride and analogous chlorides. Alkaline earth difluorides possess strong ionic bonds but are insoluble in water, with the exception of beryllium difluoride, which also exhibits some covalent character and has a quartz-like structure. Rare earth elements and many other metals form mostly ionic trifluorides.
Covalent bonding first comes to prominence in the tetrafluorides: those of zirconium, hafnium and several actinides are ionic with high melting points, while those of titanium, vanadium, and niobium are polymeric, melting or decomposing at no more than 350 °C (660 °F). Pentafluorides continue this trend with their linear polymers and oligomeric complexes. Thirteen metal hexafluorides are known, all octahedral, and are mostly volatile solids but for liquid MoF
₆ and ReF
₆, and gaseous WF
₆. Rhenium heptafluoride, the only characterized metal heptafluoride, is a low-melting molecular solid with pentagonal bipyramidal molecular geometry. Metal fluorides with more fluorine atoms are particularly reactive.
Fluorine