Rhodium (Rh) Revision Guide

Rhodium (Rh)

Rhodium (Rh) is a rare, silvery-white, hard, and chemically inert transition metal, belonging to Group 9 and Period 5 of the periodic table. It is a platinum group metal.

Atomic Model Details

• Atomic Number (Z): 45
  • Number of Protons: 45
  • Number of Electrons: 45 (in a neutral atom)
• Atomic Mass (Average): 102.90550 u
• Isotopes: The most stable and common isotope is Rhodium-103 ($^{103}\text{Rh}$).
  • Number of Neutrons in $^{103}\text{Rh}$: 103 - 45 = 58
• Atomic Size (Metallic Radius): 134 pm

Electronic Configuration & Shell Diagram Representation

• Electronic Configuration: [Kr] 4d⁸ 5s¹
  • Expanded: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d⁸ 5s¹
• Shell Diagram Representation:
  • K-shell (n=1): 2 electrons
  • L-shell (n=2): 8 electrons
  • M-shell (n=3): 18 electrons
  • N-shell (n=4): 16 electrons (consisting of 4s² 4p⁶ 4d⁸)
  • O-shell (n=5): 1 electron (consisting of 5s¹)
  • Note: The 4d⁸ 5s¹ configuration is an exception to the Aufbau principle, where an electron from the 5s orbital is promoted to the 4d orbital to achieve a more stable configuration (nearly half-filled or fully-filled d-subshell, though 4d⁸ is not exactly that, it’s energetically preferred over 4d⁷ 5s²).

Periodic Trends

• Ionization Enthalpy (IE):
  • First Ionization Enthalpy (IE₁): 719.7 kJ/mol (Energy required to remove the first electron from a neutral gaseous atom).
  • Second Ionization Enthalpy (IE₂): 1740 kJ/mol (Energy required to remove the second electron).
• Electronegativity:
  • Pauling Scale: 2.28 (Indicates a relatively high tendency to attract electrons in a chemical bond, characteristic of noble metals).
• Electron Gain Enthalpy: Generally positive (endothermic), indicating low affinity for an additional electron, and thus energy is absorbed rather than released when an electron is gained.
• Atomic Radius: 134 pm (Metallic radius). Consistent with its position in the d-block, showing typical transition metal atomic radii.

Key Physical Properties

• Density: 12.41 g/cm³ (at 20 °C)
• State at Standard Temperature and Pressure (STP): Solid
• Color: Silvery-white, lustrous
• Melting Point: 1964 °C (2237 K)
• Boiling Point: 3695 °C (3968 K)
• Crystal Structure: Face-centered cubic (FCC)