Niobium (Nb)
Niobium (Nb) is a transition metal with atomic number 41 and a standard atomic weight of 92.906. At room temperature it is a solid that melts at 2,477 °C and boils at 4,741 °C.
Niobium key facts
Niobium at a glance
Identity
| Symbol | Nb |
|---|---|
| Atomic number (Z) | 41 |
| Atomic weight | 92.906 ± 0.001 (CIAAW 2024) |
| Category | Transition metal |
| Group | 5 |
| Period | 5 |
| Block | d-block |
| CAS number | 7440-03-1 |
Atomic properties
| Electron configuration | [Kr] 4d4 5s1 Full: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d4 5s1 |
|---|---|
| Electrons per shell | 2, 8, 18, 12, 1 |
| Oxidation states | +5 Less common: -3, -1, 0, +1, +2, +3, +4 |
| Electronegativity (Pauling) | 1.6 |
| First ionisation energy | 6.759 eV (652.1 kJ/mol) 2nd: 14.32 eV · 3rd: 25.04 eV |
| Electron affinity | 0.917 eV |
| Atomic radius (empirical) | 145 pm |
| Covalent radius | 147 pm |
| Van der Waals radius | 218 pm |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Melting point | 2,477 °C · 4,490.6 °F · 2,750.15 K |
| Boiling point | 4,741 °C · 8,565.8 °F · 5,014.15 K |
| Density | 8.57 g/cm³ |
| Specific heat capacity | 0.265 J/(g·K) |
| Thermal conductivity | 53.7 W/(m·K) |
| Crystal structure | Body-centred cubic |
Isotopes & abundance
| Natural occurrence | Primordial |
|---|---|
| Radioactive | No |
| Natural isotopes (abundance) | 93Nb 100% |
| Stable isotopes | 4 |
| Known isotopes | 38 |
| Abundance in Earth's crust | 20 mg/kg |
| Abundance in seawater | 0.00001 mg/L |
Atomic weights: CIAAW Abridged Standard Atomic Weights 2024. Other properties: standard reference compilations, checked October 2026; predicted values are marked.
Niobium electron configuration
Niobium has 41 electrons. Written in short form, its ground-state configuration is [Kr] 4d4 5s1 — the electrons of the noble gas krypton, plus 4d4 5s1.Written out in full: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d4 5s1.
An exception to the filling rule. The simple aufbau (Madelung) order predicts 5s2, 4d3, but niobium actually has 5s1, 4d4. Half-filled and filled subshells, and the close energies of the outer orbitals, make this arrangement more stable.
Discovery and name
1801 — Charles Hatchett · England.
Niobe, daughter of Tantalus in Greek myth — it was long confused with tantalum.
Known for
Added to steel for pipelines and cars. Niobium–titanium and niobium–tin superconductors are used in MRI magnets and particle accelerators.
Isotopes of niobium
Naturally occurring niobium is a mix of 1 isotope. Each has 41 protons; they differ in the number of neutrons:
| Isotope | Protons | Neutrons | Natural abundance | Stability |
|---|---|---|---|---|
| 93Nb | 41 | 52 | 100% | stable |
38 isotopes of niobium are known in our data set (half-lives as published in nuclear data tables).
Niobium compared with group 5
The other elements in group 5, from top to bottom of the table: