Fluorine (F) - Atomic Structure & Chemical Properties

1. Atomic Structure of Fluorine (F)

Fluorine is the ninth element in the periodic table, belonging to Group 17 (halogens) and Period 2.

1.1. Subatomic Particles

• Atomic Number (Z): 9
  • Number of Protons: 9
  • Number of Electrons: 9 (in a neutral atom)
• Mass Number (A): Approximately 19 (for the most common isotope, ¹⁹F)
  • Number of Neutrons: A - Z = 19 - 9 = 10

1.2. Atomic Size

• Covalent Radius: ~71 pm (picometers)
• Fluorine has the smallest atomic radius among the halogens due to its high effective nuclear charge and the absence of inner d-orbitals.

2. Electronic Configuration

2.1. Electronic Configuration Notation

• Ground State Configuration: 1s² 2s² 2p⁵
• Noble Gas Configuration: [He] 2s² 2p⁵

2.2. Shell Diagram Representation

• K-shell (n=1): Contains 2 electrons.
• L-shell (n=2): Contains 7 electrons (valence shell).
  • This arrangement indicates 7 valence electrons, contributing to its high reactivity and tendency to gain one electron to achieve a stable octet configuration (like Neon).

3. Periodic Trends

Fluorine exhibits extreme values in several periodic trends due to its small size and high effective nuclear charge.

3.1. Ionization Enthalpy (IE₁)

• First Ionization Enthalpy: 1681 kJ/mol
• Fluorine has a very high ionization enthalpy. This is the highest among all elements in Period 2 and generally very high among all elements, reflecting the strong attraction of the nucleus for its valence electrons, making it difficult to remove an electron.

3.2. Electronegativity

• Pauling Scale Electronegativity: 4.0
• Fluorine is the most electronegative element in the periodic table. This signifies its unparalleled ability to attract shared electrons towards itself in a covalent bond.

3.3. Electron Gain Enthalpy (ΔH_eg)

• Electron Gain Enthalpy: -328 kJ/mol
• Fluorine has a highly negative electron gain enthalpy, meaning it readily accepts an electron to achieve a stable noble gas configuration (Neon). This process is highly exothermic. Despite its high electronegativity, its electron gain enthalpy is slightly less negative than Chlorine’s due to the small size of the fluorine atom, leading to significant inter-electronic repulsion when an extra electron enters the compact 2p subshell.

3.4. Atomic Radius

• Covalent Radius: ~71 pm
• Van der Waals Radius: ~147 pm
• Fluorine has the smallest atomic radius among the halogens and one of the smallest among all elements, primarily due to the high effective nuclear charge acting on its valence electrons in the second shell.

4. Key Physical Properties

4.1. Physical State

• At Room Temperature (25 °C): Gas

4.2. Color

• Gas: Pale yellow

4.3. Density

• Gas Density (at STP): 1.696 g/L

4.4. Melting Point

• Melting Point: -219.62 °C (53.53 K)

4.5. Boiling Point

• Boiling Point: -188.12 °C (85.03 K)