Iodine (I): Atomic Structure & Chemical Properties

Atomic Model Details of Iodine (I)

Iodine (I) is a Group 17 element, a halogen.

Subatomic Particles

• Atomic Number (Z): 53
  • Number of Protons: 53
  • Number of Electrons: 53 (in a neutral atom)
• Mass Number (A): Approximately 127 (for the most common isotope, $^{127}\text{I}$)
  • Number of Neutrons: A - Z = 127 - 53 = 74

Atomic Size

• Covalent Radius: ~139 pm
• Van der Waals Radius: ~215 pm

Electronic Configuration & Shell Diagram

Electronic Configuration

• Full Configuration: $1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^2 4p^6 4d^{10} 5s^2 5p^5$
• Noble Gas Configuration: $[\text{Kr}] 4d^{10} 5s^2 5p^5$
• Valence Shell Configuration: $5s^2 5p^5$ (indicating 7 valence electrons)

Shell Diagram Representation (Textual)

• K-shell (1st shell): 2 electrons
• L-shell (2nd shell): 8 electrons
• M-shell (3rd shell): 18 electrons
• N-shell (4th shell): 18 electrons
• O-shell (5th shell - Valence shell): 7 electrons

Periodic Trends of Iodine

Ionization Enthalpy (First)

• Value: 1008.4 kJ/mol
• Trend: As we move down Group 17, the ionization enthalpy decreases due to increasing atomic size and shielding effect, making it easier to remove the outermost electron. Iodine has a lower ionization enthalpy compared to F, Cl, and Br.

Electronegativity

• Value (Pauling scale): 2.66
• Trend: Electronegativity decreases down Group 17 due to increasing atomic size and greater distance of valence electrons from the nucleus. Iodine is less electronegative than F, Cl, and Br.

Electron Gain Enthalpy

• Value: -295.2 kJ/mol
• Trend: Electron gain enthalpy generally becomes less negative (less exothermic) down Group 17, although chlorine (Cl) has a more negative electron gain enthalpy than fluorine (F). For iodine, the larger atomic size and diffused electron cloud lead to a less exothermic electron gain enthalpy compared to Cl and Br.

Atomic Radius

• Value: 139 pm (covalent radius)
• Trend: Atomic radius increases down Group 17 due to the addition of new electron shells. Iodine has the largest atomic radius among the stable halogens (F, Cl, Br, I).

Key Physical Properties

Density

• Value: 4.93 g/cm³ (at 20°C, solid state)

State at Room Temperature (25°C)

• Solid: Iodine exists as a crystalline solid at room temperature.

Color

• Solid: Lustrous violet-black solid.
• Vapor: Sublimes to form a vibrant violet-purple gas.

Melting Point (MP)

• Value: 113.7 °C

Boiling Point (BP)

• Value: 184.3 °C