Anomalous Behaviour of Fluorine and Chemical Properties for JEE

Fluorine is the most reactive of all the halogens. This is due to the F₂ molecule's low F-F dissociation enthalpy. It has the ability to displace other halogens from salt solutions. Fluorine reacts with hydrogen in the dark at low temperatures, whereas the other halogens do not. Fluorine combines directly with non-metals such as carbon,silicon, nitrogen and others to form fluorides. The other halogens, on the other hand, do not combine directly with these elements, which results in fluorine’s anomalous behaviour.

In this article, we will come across various other anomalous behaviour of fluorine, its chemical properties and examples of its anomalous behaviour.

Chemical Properties of Fluorine

Fluorine's chemical properties are discussed as follows:

• Hydrogen Bonding: Fluorine has the highest electronegativity of any halogen. Fluorine forms strong hydrogen bonds in its hydride, unlike other halogens, because the H-F bond is highly polar in nature. As a result, HF is a liquid at room temperature, whereas other hydrogen halides are gaseous.

• Oxidation State: Fluorine, being the smallest and most electronegative element, has only one oxidation state -1, whereas other halogens have variable oxidation states such as -1,+1, +3, +5, and +7.

• Polyhalide Ions: Since fluorine has the smallest size and d-orbitals are not available in its valence shell, it has no tendency to form polyhalide ions, whereas other halogens do.

• Oxidising Nature: Fluorine has a higher tendency to accept an electron due to its high electronegativity and electron affinity. As a result, it is a more potent oxidising agent than other members of the halogen family. Although the electron gain enthalpy of fluorine is less negative than that of chlorine, it is a more powerful oxidising agent. This is because fluorine has a higher standard reduction potential (i.e. +2.87 V) than chlorine (i.e. =1.36 V).

• Reactivity: Out of all the halogens, fluorine is the most reactive. It is capable of displacing other halogens from salt solutions. It reacts with hydrogen in the dark and at low temperatures and with gold and platinum, but not with the other noble metals. Fluorine reacts violently and transforms into hydrofluoric acid when it comes into contact with moisture. Hydrogen fluoride (HF) can deeply penetrate biological tissues and continue to harm tissue if it is not neutralised.

Explain Anomalous Behaviour of Fluorine

Fluorine exhibits unusual behaviour when compared to the other halogens in the group. It differs from the other members. Reasons for anomalous behaviour of fluorine are discussed below:

• Fluorine gas (F₂) is in its simplest form.

• It has maximum electronegativity (electronegativity of 4).

• The F-F bond dissociation enthalpy is also low.

• d-orbitals are not available in the valence shell.

Examples of Anomalous Behaviour of Fluorine

Here are two examples:

1. Fluorine has an oxidation state of –1 due to the non-availability of d-orbitals in its valence shell. So, it forms compounds such as OF₂, whereas all other halogens form compounds such as OCl₂, ClO₂, Cl₂O₆, Cl₂O₇, BrO₃, I₂O₅, etc. due to the positive oxidation states of +1, +3, +5 and +7 in addition to the oxidation state of –1.

2. The dissociation energy of the F–F bond is lower than that of the Cl–Cl bond. Due to its small size, the lone pairs on the two fluorines repel each other more strongly.

Conclusion

In this article, we learned how fluorine differs from other members of its family, its relation to other members, the reasons for the anomalous behaviour of fluorine, the chemical properties which fluorine possesses, and the examples of its anomalous behaviour.

Fluorine belongs to periodic table group 17, known as halogens. Thus, fluorine, with atomic number 9 and electronic configuration 2,7 is the first member of the halogen family. Its behaviour and properties, however, differ from those of the other halogen family members. It behaves abnormally due to its extremely small atomic size, high electronegativity, low F-F bond dissociation enthalpy, and lack of vacant d-orbital. It has the highest reducing power and an oxidation state of -1.