Uranium (U) - Atomic Structure & Chemical Properties

Introduction to Uranium (U)

Uranium (U) is a silvery-white radioactive metallic element belonging to the actinide series. It is a critical element in nuclear technology due to its fissile isotopes.

Atomic Model Details

Uranium’s atomic structure is characterized by the following:

• Atomic Number (Z): 92
  • This indicates 92 protons in the nucleus.
• Number of Electrons: 92 (in a neutral atom).
• Mass Number (for the most common isotope, Uranium-238, U-238): 238
  • Number of Neutrons: Mass Number - Atomic Number = 238 - 92 = 146 neutrons.
• Atomic Radius:
  • Metallic Radius: Approximately 156 pm (picometers).
  • Covalent Radius: Approximately 158 pm.

Electronic Configuration & Shell Diagram

Uranium’s electronic configuration determines its chemical behavior.

• Electronic Configuration: [Rn] 5f³ 6d¹ 7s²
  • The term [Rn] represents the electron configuration of Radon, the noble gas preceding Uranium, which is 1s² 2s²2p⁶ 3s²3p⁶3d¹⁰ 4s²4p⁶4d¹⁰4f¹⁴ 5s²5p⁶5d¹⁰ 6s²6p⁶.
• Shell Diagram Representation:
  • The electrons are distributed in shells (energy levels) as follows:
    • K-shell (n=1): 2 electrons
    • L-shell (n=2): 8 electrons
    • M-shell (n=3): 18 electrons
    • N-shell (n=4): 32 electrons
    • O-shell (n=5): 21 electrons (5s²5p⁶5d¹⁰5f³)
    • P-shell (n=6): 9 electrons (6s²6p⁶6d¹)
    • Q-shell (n=7): 2 electrons (7s²)
  • This can be summarized as 2, 8, 18, 32, 21, 9, 2.

Periodic Trends

As an actinide, Uranium exhibits specific periodic trends:

• Ionization Enthalpy:
  • First Ionization Enthalpy (IE₁): 597.6 kJ/mol
  • Second Ionization Enthalpy (IE₂): 1420 kJ/mol
  • Third Ionization Enthalpy (IE₃): 1900 kJ/mol
  • These values indicate that Uranium, like other metals, has a relatively low ionization enthalpy, meaning it readily loses electrons to form positive ions.
• Electronegativity:
  • Pauling Scale: 1.38
  • Uranium has a low electronegativity, indicating its metallic character and tendency to donate electrons rather than attract them in chemical bonds.
• Electron Gain Enthalpy:
  • For most metals, especially actinides, electron gain enthalpy is typically positive or close to zero, as they generally tend to lose electrons rather than gain them. Precise negative values are not commonly reported or significant for its chemistry.
• Atomic Radius:
  • Metallic Radius: ~156 pm. The atomic radius is relatively large due to the presence of multiple electron shells.

Key Physical Properties

Uranium possesses distinct physical characteristics:

• Density: 19.1 g/cm³ (at 20 °C)
  • Uranium is an exceptionally dense metal, almost twice as dense as lead.
• State at Room Temperature: Solid
• Color: Silvery-white to grey. It tarnishes quickly in air to a dull grey or black oxide layer.
• Melting Point: 1132 °C
• Boiling Point: 4131 °C