Question

Give reasons for the following: (a) Fluorine exhibits only (-I) oxidation state while the other halogens can show higher oxidation states. (b) HF has the highest boiling point while lowest acidic strength among the halogen acids. (c) \(\mathrm{F}_{2}\) is the strongest oxidising agent.

Short answer

Fluorine always exhibits -1 oxidation state due to its highest electronegativity and no available d-orbitals. HF's high boiling point and lowest acidic strength amongst halogen acids can be attributed to its high polarity and strong bond . F2 is the strongest oxidizing agent due its extremely high electronegativity, small size and the stability it gains after reduction to F-.

Step-by-step solution

Explanation of Fluorine Oxidation State

Fluorine is the most electronegative element in the periodic table. Thus, it always attracts electron to gain a stable electronic configuration of the nearest noble gas, and forms a \( \mathrm{-1} \) oxidation state. It does not have d-orbitals to expand its covalency beyond one, so it cannot show a positive oxidation state. Hence, Fluorine exhibits only a -1 oxidation state, while other halogens, which have empty d-orbitals, can exhibit positive oxidation states.

Explanation of HF Boiling Point and Acidic Strength

HF has the highest boiling point among halogen acids due to the high polarity of the bond and the presence of strong hydrogen bonds. The acidic strength of a hydrogen halide is determined by the ease with which it can lose a proton (H+). In comparison to other hydrogen halides, HF is least willing to donate a proton due to its strong H − F bond, resulting in its least acidic strength.

Explanation of F2 as the Strongest Oxidising Agent

F2 is the strongest oxidizing agent because of its extremely high electronegativity and small size, which contributes to a strong desire to gain electrons. Also, when F2 is reduced to F-, it forms an exceptionally stable ion. The ability for elements and compounds to attract and accept electrons is what makes them potent oxidation agents. Thus, F2, having the strongest ability to attract electrons, is the strongest oxidizing agent.

Key concepts

Oxidation States

Understanding oxidation states is crucial for grasping how elements interact chemically. An oxidation state indicates the degree of oxidation (loss of electrons) of an element within a compound. For halogens, which are known for their high electronegativities, it is often negative. However, some can exhibit positive oxidation states when bonded with elements that are more electronegative than themselves.

Fluorine, being the most electronegative element in the periodic table, is unique in that it always exhibits a \(-1\) oxidation state. It cannot exceed this due to its lack of available d-orbitals for bonding. Other halogens, like chlorine or bromine, possess empty d-orbitals, enabling them to form compounds in higher oxidation states when bonded to highly electronegative elements such as oxygen.

• Fluorine: Always -1
• Chlorine and other halogens: Possible positive states due to d-orbitals

Fluorine

Fluorine is known for being the most electronegative element, which greatly influences its chemical behavior. This electronegativity means fluorine has a strong tendency to attract electrons towards itself. Because of this characteristic, it often forms stable compounds where it achieves a noble gas electronic configuration by gaining one electron and achieving a \(-1\) oxidation state.

Fluorine does not participate in further sharing or losing electrons due to its high electronegativity and lack of d-orbitals. This property limits fluorine's covalency to one, preventing the formation of compounds with fluorine in any other oxidation state besides \(-1\).

• High electronegativity
• Lacks d-orbitals
• Forms stable \(-1\) ion

Hydrogen Bonding

Hydrogen bonding plays a key role in determining the physical properties of substances, such as boiling and melting points. It occurs when a hydrogen atom, covalently bonded to a highly electronegative element (like fluorine, oxygen, or nitrogen), experiences attraction to another electronegative atom.

In the case of hydrogen fluoride (HF), strong hydrogen bonds form between the hydrogen and fluorine atoms, resulting in a higher boiling point relative to other hydrogen halides like HCl or HBr. The hydrogen bonding requires more energy to break, thus HF remains in the liquid phase at higher temperatures, unlike other halogen acids that are gases under similar conditions.

• Strong intermolecular forces
• Higher energy required to break bonds
• HF: Higher boiling point due to strong hydrogen bonds

Oxidizing Agents

Oxidizing agents are substances that gain electrons during chemical reactions, which leads to the oxidation of another substance. They are characterized by their ability to accept electrons easily. Fluorine gas (\( ext{F}_2\)) is the strongest oxidizing agent known, thanks to its extremely high electronegativity and small atomic radius.

This small size means fluorine can get very close to other atoms, allowing it to exert a strong pull on the electrons of a reacting substance. When \( ext{F}_2\) is reduced by gaining electrons to form fluoride ions (\( ext{F}^-\)), it forms an exceptionally stable ion due to the achievement of a noble gas configuration. The energetic feasibility of this process makes \( ext{F}_2\) an exceptionally strong oxidizing agent.

• High electronegativity
• Small atomic size
• Forms stable fluoride ion