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Anomalous Behaviour of Fluorine and Chemical Properties for JEE

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Anomalous Behaviour of Fluorine - A Brief Description

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.

  1. 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.


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.

Last updated date: 23rd Sep 2023
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FAQs on Anomalous Behaviour of Fluorine and Chemical Properties for JEE

1. What is anomalous behaviour?

Anomalous behaviour is defined as the abnormal behaviour of elements in a group as a result of their small size, electronegativity and lack of d-orbitals. Anomalous behaviour is distinct behaviour displayed by a member of a group. Elements in a group should have the same properties, but some have different properties known as anomalous properties. 

In comparison to other alkaline earth metals, beryllium possesses some different properties. It has a high melting and boiling point and does not react with acid. Therefore, beryllium is said to have anomalous behaviour.

2. What are halogens? Mention their properties?

Fluorine, chlorine, bromine, iodine, and astatine are the five elements that make up the halogens and the group containing them is group 17.


Many properties of halogens are similar to each other, including:

  • When combined with hydrogen, they all produce acids.

  • They are all fairly poisonous.

  • They combine easily with metals to form salts.

  • Their outer shell contains seven valence electrons.

  • They have high reactivity and are electronegative.

  • In their pure form, they are all diatomic molecules (two atoms).

3. What are the uses of halogens?

Halogens are used as,

  • Bromine is used in the extraction of gold and in the drilling of oil and gas wells. It is used as a fire retardant, refrigerating and is also found in fire extinguishing fluids.

  • Chlorine is used to disinfect and purify and treat drinking water. It is a bleaching agent used in laundries. It is used in the food, leather, textile and pulp and paper industries as a bleaching agent.

  • Fluorine compounds are used in toothpaste to prevent tooth decay. It is also used in the conversion of uranium tetrafluoride to uranium hexafluoride and chlorine trifluoride and is used in nuclear reactor fuel.