Fluorine

Fluorine (F) is the first element in the periodic table's halogen group (Group 17). It has an atomic number of 9 and an atomic weight of 19. Fluorine is a gas at room temperature and is the most electronegative element, which makes it highly reactive, particularly as it is positioned at the top of the halogen group.

1.0Fluorine (Super Halogen)

Fluorine gas, with the chemical formula F₂, is also known as difluoride. It consists of two fluorine (F) atoms and is highly reactive, interacting with almost all other elements except argon, neon, and helium. In its gaseous state, fluorine appears to be pale yellow. When liquefied, it takes on a bright yellow hue, and in its solid state, it can be either transparent or opaque, with the solid forms known as alpha and beta.

• Discovered by Henri Moissan in 1886.
• Found in combined states such as Fluorspar (CaF₂,)Cryolite (Na₃AlF₆), and Fluorapatite (CaF₂·3Ca₃(PO₄)₂).
• Present in small amounts in soil, river water, bones, and teeth of animals.

2.0Anomalous Behavior of Fluorine

Like other elements in the p-block of the second period, Fluorine exhibits several anomalous properties.

• Notably, based on trends observed in other halogens, fluorine's ionisation enthalpy, electronegativity, and electrode potentials are higher than expected. 
• Conversely, its ionic and covalent radii, melting and boiling points, bond dissociation enthalpy, and electron gain enthalpy are lower than anticipated.

This anomalous behaviour can be attributed to fluorine's small atomic size, exceptionally high electronegativity, low F-F bond dissociation enthalpy, and the absence of d-orbitals in its valence shell. Due to these factors, most reactions involving fluorine are highly exothermic, as they form small and strong bonds with other elements.

Unlike other halogens, which form multiple oxoacids, fluorine forms only one. Due to strong hydrogen bonding, hydrogen fluoride (HF) is a liquid with a boiling point of 293 K, whereas other hydrogen halides exist as gases.

3.0Common Compounds Of  Fluorine

Fluorine's small atomic size makes it challenging to find in ionic compounds. However, fluorine forms various compounds due to its highly electrophilic and reactive nature. Some of the most widely used fluorine-containing compounds include:

• Calcium Fluoride (CaF₂)
• Xenon Difluoride (XeF₂)
• Hydrogen Fluoride (HF)
• Uranium Hexafluoride (UF₆)
• Sodium Monofluorophosphate (Na₂PO₃F)
• Sodium Fluoride (NaF)
• Stannous(II) Fluoride (SnF₂)
• Dichlorodifluoromethane (CF₂Cl₂)

4.0Preparation of Fluorine Gas

Fluorine is predominantly found in the form of fluoride compounds. These fluoride compounds can be converted to hydrogen fluoride (HF) by reacting calcium fluoride (CaF₂) with sulfuric acid (H₂SO₄): 

• CaF₂​+H_2​SO₄​→2HF+CaSO₄​.

Fluorine can also be produced by the degradation of hexafluorosilicic acid (H₂SiF₆), which releases hydrogen fluoride (HF) through hydrolysis: 

• H₂​SiF₆​→2HF+SiF₄​.

The silicon tetrafluoride (SiF₄) formed can further react with water to produce additional hydrogen fluoride (HF) and silicon dioxide (SiO₂): 

• SiF₄​+2H₂​O→4HF+SiO₂​.
  

Industrial Extraction of Fluorine

Fluorine is an element of significant industrial importance, and its extraction is carried out in factories primarily through the electrolysis of potassium hydrogen fluoride in anhydrous hydrofluoric acid. In this process, the anode is made of calcium, and hydrogen gas is released at the anode, while pure diatomic fluorine (F₂) is liberated at the cathode.

The electrolysis reactions can be observed in the following equations:

At the Anode: 2HF→H₂​+2F⁻ 

At the Cathode: 2F⁻→F_2​

For optimal cell operation, a low temperature of around 360 K is required. A water jacket maintained at 350 K maintains this temperature.

Fluorine is naturally present in the air and occurs in combined forms with other elements in the Earth's crust.

5.0Physical Properties of Fluorine gas  

Appearance: Pale yellow gas

Atomic Mass: 18.998403 g/mol

Melting Point: -219.67°C

Boiling Point: -188.11°C

Density: 1.8 × 10⁻³ g/cm³

Reactivity:

• Combines easily with metals, non-metals, metalloids, and some noble gases
• Reacts with glass and water

6.0Chemical Properties of Fluorine Gas

Reactions:

• With Water (H₂O): When fluorine reacts with water, it produces hydrogen fluoride (HF) and oxygen gas (O₂).

2F_2​ + 2H_2​O → 2HF + O₂​

• With Sodium Hydroxide (NaOH): When fluorine reacts with sodium hydroxide, it yields sodium fluoride (NaF), oxygen difluoride (OF₂), and water (H₂O).

F₂​ + 2NaOH → 2NaF + OF₂​ + H_2​O

• With Metals and Non-metals: Reacts directly with Al, Mg, C, P, S, As, Sb, Br2, I2, forming fluorides. Cu and Hg form a protective coating of fluoride.
• With Xenon: Forms XeF₂ (linear, sp³d hybridisation), XeF₄ (square planar, sp³d² hybridisation), XeF₆ (distorted octahedral, sp³d³ hybridisation).
• With Hydrogen: Reacts even in the dark.
• With Ammonia: Forms NH₄F and N₂ (non-explosive).
• With H₂S: Reacts vigorously, forming HF and S.
• With Hydrocarbons: It reacts violently (e.g., with CH₄). Fluorination is done in the presence of N₂ and a copper catalyst to control the reaction.

7.0Uses of Fluorine Gas

• Used in preparing uranium hexafluoride (UF₆) for the nuclear fuel cycle.
• It is added to toothpaste to prevent dental cavities.
• Used in drinking water fluoridation to prevent dental cavities.
• Serves as a strong oxidising agent.
• Used in the manufacturing of Teflon (polytetrafluoroethylene).
• Employed in light bulbs.
• Molecular and atomic fluorine are used in semiconductor manufacturing processes, particularly for Plasma Etching, MEMS fabrication, and flat panel display production.
• Fluorinated compounds can be used to map the circulatory system and detect disorders.
• Proposed for use in optoelectric nuclear batteries.