72 - Hafnium transition metal
Discovered by Dirk Coster in 1923
Hafnium is a chemical element with symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in zirconium minerals. Its existence was predicted by Dmitri Mendeleev in 1869, though it was not identified until 1923, making it the penultimate stable element to be discovered (rhenium was identified two years later).
H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og
57-71 La-Lu Lanthanides
89-103 Ac-Lr Actinides
| Shell | Electrons | Orbitals |
|---|---|---|
| 1 | 2 | 2 in 1s |
| 2 | 8 | 2 in 2s + 6 in 2p |
| 3 | 18 | 2 in 3s + 6 in 3p + 10 in 3d |
| 4 | 32 | 2 in 4s + 6 in 4p + 10 in 4d + 14 in 4f |
| 5 | 10 | 2 in 5s + 6 in 5p + 2 in 5d |
| 6 | 2 | 2 in 6s |
steel gray Appearance
178 u Atomic Mass
1.55 Å Atomic Radius
4.88k K Boiling Point
4 Group
4 Common Oxidation States
1.75 Å Covalent Radius
13.3 g/cm³ Density
17.2 kJ/mol Electron Affinity
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d2 Electron Configuration
[Xe] 4f14 5d2 6s2 Electron Configuration (semantic)
1.3 Electronegativity
72 Electrons
6.83 eV First Ionization Energy
4 ICSD Oxidation States
658.5, 1440, 2250, 3216 kJ/mol Ionization Energies
2.5k K Melting Point
50 Mendeleev Number
25.7 J/(mol·K) Molar Heat
6 Number of Shells
106 Neutrons
72 Atomic Number
17 Number of Isotopes
2, 3, 4 Oxidation States
6 Period
Solid Phase
72 Protons
2, 8, 18, 32, 10, 2 Electron Shell Occupations