Anomalous Properties of Fluorine

Fluorine shows anomalous properties due to its small size and high electronegativity.

The low F-F bond dissociation enthalpy and absence of d-orbitals are also responsible for its anomalous behaviour.

Let us study a few anomalous properties of fluorine.

Ionisation enthalpy, electronegativity, and electrode potentials are all higher for fluorine than expected, compared to other halogens.

On the other hand, ionic and covalent radii, melting and boiling points, and electron gain enthalpy are lower than expected.

Because of its small size, fluorine forms hydrogen bonds in its compounds.

For example, hydrogen fluoride (HF) is a liquid whereas other halogen acids are gases.

This is because hydrogen bonding exists in HF, unlike other halogen acids.

Also, fluorine has only one oxidation state (-1). It does not show positive oxidation states.

This is because of its electronegative nature and absence of d-orbitals.

On the other hand, other halogens can show positive oxidation states of +1, +3, +5 and +7.

Another anomalous property is that fluorine forms only one oxoacid. The other halogens form a number of oxoacids.

All halogens react with hydrogen to form hydrogen halides. The affinity for hydrogen, however, decreases from fluorine to iodine.

The acidic strength of these hydrohalic acids is the lowest for HF and the highest for HI.

HF is the most stable and HI is the least. This is because of the decrease in bond (H–X) dissociation enthalpy.

HF cannot be stored in glassware because it reacts with silicates, while other halogen acids do not react.

Another difference is that fluorine reacts with water energetically, oxidizing it to ozone and oxygen.

On the contrary, other halogens decompose water differently and at a very slow rate.

Lastly, fluorides have the highest ionic character. Other halides have covalent character.

Revision

Anomalous behavior of fluorine is because of its small size, high electronegativity, low F-F bond dissociation enthalpy, and absence of d-orbitals.

Ionisation enthalpy, electronegativity, and electrode potentials are all higher for fluorine than expected, compared to other halogens.

Ionic and covalent radii, melting and boiling points and electron gain enthalpy are lower than expected.

Because of its small size, fluorine forms hydrogen bonds in its compounds. Hydrogen fluoride (HF) is a liquid whereas other halogen acids are gases.

This is because hydrogen bonding exists in HF, unlike other halogen acids.

Fluorine has only one oxidation state (-1) and does not show positive oxidation states.

It forms only one oxoacid. The other halogens form a number of oxoacids.

The acidic strength of hydrohalic acids is the lowest for HF and the highest for HI.

HF is the most stable and HI is the least stable because of the decrease in bond (H–X) dissociation enthalpy.

HF cannot be stored in glassware because it reacts with silicates.

Fluorine reacts with water energetically while other halogens decompose water at a very slow rate.

Fluorides have the highest ionic character.

The End.