Hafnium (Hf)

Atomic Model Details of Hafnium (Hf)

Hafnium (Hf) is a transition metal located in Group 4, Period 6 of the periodic table.

Atomic Number (Z): 72
- Indicates 72 protons in the nucleus.
- Indicates 72 electrons in a neutral Hafnium atom.
Atomic Mass: 178.49 u (unified atomic mass units)
- The most common isotope is Hafnium-180 (¹⁸⁰Hf).
Number of Neutrons: Varies with isotope. For the most abundant isotope (¹⁸⁰Hf), it is 180 - 72 = 108 neutrons. The average number of neutrons is approximately 106.49.
Atomic Radius:
- Metallic Radius: 156 pm
- Covalent Radius: 159 pm

Electronic Configuration & Shell Diagram

Electronic Configuration

The ground state electronic configuration of Hafnium is: [Xe] 4f¹⁴ 5d² 6s²

This configuration indicates that after the core electrons resembling Xenon (Xe), there are 14 electrons completely filling the 4f subshell, 2 electrons in the 5d subshell, and 2 electrons in the 6s subshell. The filling of the 4f orbitals accounts for the lanthanide contraction, which significantly impacts Hf’s properties.

Shell-wise Electron Distribution

The distribution of electrons in different shells (main energy levels) is as follows:

1st Shell (K): 2 electrons (1s²)
2nd Shell (L): 8 electrons (2s² 2p⁶)
3rd Shell (M): 18 electrons (3s² 3p⁶ 3d¹⁰)
4th Shell (N): 32 electrons (4s² 4p⁶ 4d¹⁰ 4f¹⁴)
5th Shell (O): 10 electrons (5s² 5p⁶ 5d²)
6th Shell (P): 2 electrons (6s²)

Periodic Trends

Hafnium’s position in the periodic table and the presence of the filled 4f subshell (lanthanide contraction) significantly influence its periodic properties.

Ionization Enthalpy

First Ionization Enthalpy (IE₁): 658.5 kJ/mol
Second Ionization Enthalpy (IE₂): 1440 kJ/mol
Trend: The first ionization enthalpy of Hafnium is remarkably similar to that of Zirconium (Zr) (IE₁ ≈ 660 kJ/mol). This similarity is a direct consequence of the lanthanide contraction, which causes the effective nuclear charge to increase more than expected across the 5d series, leading to a smaller atomic radius and a stronger attraction of valence electrons to the nucleus.

Electronegativity

Pauling Scale Electronegativity: 1.3
Trend: Hafnium has a relatively low electronegativity, typical for a metallic element, indicating its tendency to lose electrons rather than gain them in chemical bonding. It is similar to Zirconium (1.33).

Electron Gain Enthalpy

Electron Gain Enthalpy: Generally positive or close to zero for metals.
Trend: Hafnium, being a metal, does not readily accept electrons. Its electron gain enthalpy is not significantly negative, reflecting its metallic character and low affinity for extra electrons.

Atomic Radius

Metallic Radius: 156 pm
Trend: Due to the lanthanide contraction, Hafnium’s atomic radius (156 pm) is almost identical to that of Zirconium (160 pm), its lighter congener in the same group. This unusual similarity in atomic size contributes to the highly similar chemical properties of Hf and Zr, making their separation challenging.

Key Physical Properties

Hafnium is a lustrous, silvery, ductile metal.

Density: 13.31 g/cm³ (at 20 °C)
State at STP: Solid
Color: Silvery-gray, lustrous
Melting Point: 2233 °C (2506 K)
Boiling Point: 4603 °C (4876 K)
Crystal Structure: Hexagonal close-packed (hcp) at room temperature.

Hafnium (Hf) - Atomic Structure & Chemical Properties