Cerium (Ce) Revision Guide

Cerium (Ce): Atomic Structure and Chemical Properties

Cerium (Ce) is a chemical element with atomic number 58. It is the most abundant of the lanthanide elements.

Atomic Number (Z): 58
- Indicates 58 protons in the nucleus.
- A neutral Cerium atom has 58 electrons.
Atomic Mass (A): Approximately 140.12 u (atomic mass units).
- Number of neutrons (for the most common isotope, Ce-140) = Mass Number - Atomic Number = 140 - 58 = 82 neutrons.
Atomic Size:
- Metallic Radius: 182.5 pm (picometers) for coordination number 12.

Electronic Configuration: [Xe] 4f¹ 5d¹ 6s²
- This configuration is characteristic of many lanthanides, where the 5d orbital is occupied before the 4f orbital is fully filled, contributing to their chemical behaviour.
Shell Diagram Representation (Electrons per shell):
- 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): 19 electrons (4s² 4p⁶ 4d¹⁰ 4f¹)
- O-shell (n=5): 9 electrons (5s² 5p⁶ 5d¹)
- P-shell (n=6): 2 electrons (6s²)
- Total electrons = 2 + 8 + 18 + 19 + 9 + 2 = 58.

Ionization Enthalpy:
- First Ionization Enthalpy: 534.4 kJ/mol (energy required to remove the first electron).
- Second Ionization Enthalpy: 1047 kJ/mol (energy required to remove the second electron).
- Third Ionization Enthalpy: 1949 kJ/mol (energy required to remove the third electron).
- Cerium readily loses its 6s and 5d electrons to form Ce³⁺ ions, which is the most common oxidation state. The relatively low first and second ionization energies facilitate this.
Electronegativity (Pauling scale): 1.12
- Cerium is an electropositive metal, indicating its tendency to lose electrons rather than gain them.
Electron Gain Enthalpy: Not typically measured or relevant for electropositive metals like Cerium; values are usually positive or close to zero, reflecting no tendency to gain electrons.
Atomic Radius: As noted above, the metallic radius is 182.5 pm. The atomic radius generally decreases slightly across the lanthanide series (lanthanide contraction), but Cerium is at the beginning.

Density: 6.77 g/cm³ (at 25 °C)
State at STP: Solid
Color: Silvery-white metal, which readily tarnishes to a reddish-brown oxide layer upon exposure to air.
Melting Point: 795 °C
Boiling Point: 3443 °C