Samarium (Sm) Revision Guide
Samarium (Sm) Overview
Samarium is a lanthanide element, a member of the f-block, and is characterized by its silvery-white luster and relatively high stability for a rare-earth metal.
Atomic Model Details
Fundamental Particles
- Atomic Number (Z): 62
- Protons: 62 (in the nucleus)
- Electrons: 62 (in a neutral atom)
- Neutrons: The most abundant isotope, Samarium-152 ($^{152}$Sm), contains 90 neutrons (152 - 62). The average number of neutrons for naturally occurring isotopes is approximately 88.36, based on an average atomic mass of 150.36 u.
Atomic Size
- Metallic Radius (12-coordination): Approximately 180 pm.
- Ionic Radius (Sm³⁺): Approximately 96.4 pm.
Electronic Configuration & Shell Diagram
Electronic Configuration
The ground state electronic configuration of Samarium (Sm) is:
[Xe] 4f⁶ 6s²
Where [Xe] represents the electronic configuration of Xenon (1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶).
Shell Diagram Representation
The distribution of electrons in different shells (main energy levels) is as follows:
- K-shell (n=1): 2 electrons (1s²)
- L-shell (n=2): 8 electrons (2s² 2p⁶)
- M-shell (n=3): 18 electrons (3s² 3p⁶ 3d¹⁰)
- N-shell (n=4): 24 electrons (4s² 4p⁶ 4d¹⁰ 4f⁶)
- O-shell (n=5): 8 electrons (5s² 5p⁶)
- P-shell (n=6): 2 electrons (6s²)
Periodic Trends
Ionization Enthalpy
- First Ionization Enthalpy (IE₁): Approximately 543.4 kJ/mol
- Second Ionization Enthalpy (IE₂): Approximately 1068 kJ/mol
- Third Ionization Enthalpy (IE₃): Approximately 2260 kJ/mol
Samarium exhibits a relatively low first ionization enthalpy due to the shielding effect of inner electrons and the relatively large atomic size, making it easy to remove the outermost 6s electrons.
Electronegativity
- Pauling Scale: Approximately 1.17
Samarium has low electronegativity, consistent with its metallic character and tendency to form positive ions.
Electron Gain Enthalpy
Electron gain enthalpy is generally not a common or favorable property for metals. For Samarium, like other lanthanides, the electron gain enthalpy is positive, indicating that energy is required to force an electron onto a neutral samarium atom. Therefore, it does not readily form anions.
Atomic Radius
As mentioned above, the metallic radius of Samarium is approximately 180 pm. Across the lanthanide series, a gradual decrease in atomic and ionic radii is observed, known as the Lanthanide Contraction, due to poor shielding by the 4f electrons.
Key Physical Properties
- Density: 7.52 g/cm³ (at 25°C)
- State at STP: Solid
- Color: Silvery-white
- Melting Point: 1072 °C (1345 K)
- Boiling Point: 1794 °C (2067 K)