Praseodymium (Pr) - Atomic Structure & Chemical Properties

Atomic Model Details

Praseodymium (Pr) is a chemical element with atomic number 59. It is a soft, silvery, ductile metal in the lanthanide series.

• Atomic Number (Z): 59
• Protons: 59
• Electrons: 59 (in a neutral atom)
• Neutrons: 82 (for the most stable isotope, Pr-141)
• Atomic Mass: 140.90765 u
• Atomic Radius (Metallic): 182 pm

Electronic Configuration & Shell Diagram

The electronic configuration of Praseodymium dictates its chemical behavior.

• Ground State Electronic Configuration: [Xe] 4f³ 6s²
  • This configuration indicates that after the stable core of Xenon ([Xe], which accounts for 54 electrons), there are three electrons in the 4f subshell and two electrons in the 6s subshell. The filling of the 6s subshell before the 4f subshell is due to the lower energy of 6s compared to 4f initially, followed by the occupation of 4f orbitals.
• 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): 21 electrons (including 3 from 4f)
  • O-shell (n=5): 8 electrons
  • P-shell (n=6): 2 electrons

Periodic Trends

The position of Praseodymium in the periodic table (f-block, lanthanide series) influences its periodic properties.

Ionization Enthalpy

• First Ionization Enthalpy (IE₁): 527 kJ/mol
• Second Ionization Enthalpy (IE₂): 1020 kJ/mol
• Trend: Lanthanides generally have relatively low ionization enthalpies due to their large atomic size and the shielding effect of inner electrons on the outermost 6s electrons, making them relatively easy to remove. There is a general, slight increase in ionization enthalpy across the lanthanide series due to the lanthanide contraction.

Electronegativity

• Pauling Scale: 1.13
• Trend: Praseodymium is an electropositive metal, exhibiting low electronegativity. Electronegativity tends to slightly increase across the lanthanide series.

Electron Gain Enthalpy

• Value: Generally positive or negligible.
• Trend: As a metal, Praseodymium has a very low tendency to accept additional electrons. Its electron gain enthalpy is not a characteristic property and is typically positive, indicating energy input is required to add an electron.

Atomic Radius

• Metallic Radius: 182 pm
• Trend: The atomic radius of Praseodymium is part of the general trend known as Lanthanide Contraction. Across the lanthanide series (from La to Lu), there is a gradual decrease in atomic and ionic radii. This is attributed to the poor shielding effect of the 4f electrons, which leads to an increased effective nuclear charge experienced by the outer electrons, pulling them closer to the nucleus.

Key Physical Properties

• Density: 6.77 g/cm³ (at 20 °C)
• State at STP: Solid
• Color: Silvery-white; tarnishes slowly in air to form a greenish oxide coating.
• Melting Point: 935 °C
• Boiling Point: 3522 °C