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Nb

Niobium

Niobium (Nb) is a transition metal with atomic number 41 and an atomic mass of 92.906. Its electron configuration is [Kr] 4d4 5s1.

Niobium key data

Symbol Nb
Atomic number 41
Atomic mass (standard atomic weight) 92.906
Molar mass 92.906 g/mol
Protons 41
Neutrons (most abundant isotope, niobium-93) 52
Electrons (neutral atom) 41
Category Transition metal
Period 5
Group 5
Block d-block
Noble gas notation [Kr] 4d4 5s1
Full electron configuration 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d4 5s1
Electrons per shell 2, 8, 18, 12, 1

Atomic mass: IUPAC CIAAW abridged standard atomic weights, 2024. Most abundant isotope: NIST Atomic Weights and Isotopic Compositions.

The values are facts and free to use; this page’s selection and presentation are © 2026 ScienceQuest.

Measured properties of niobium

From PubChem, the US National Institutes of Health. Public domain.

Melting point 2750 K (2476.9 °C), 7th of 103 by melting point
Boiling point 5017 K (4743.9 °C), 6th of 93 by boiling point
Density 8.57 g/cm³, 37th of 96 by density
State at room temperature Solid
Electronegativity 1.6 (Pauling), 50th of 95 by electronegativity
Van der Waals radius 207 pm, joint 52nd of 99 by atomic radius
First ionisation energy 6.759 eV (652.1 kJ/mol), 55th of 102 by first ionisation energy
Electron affinity 0.893 eV (86.2 kJ/mol), 26th of 57 by electron affinity
Common oxidation states +5, +3
Discovered 1801

Each rank counts down from the highest value, among the elements PubChem’s table gives one for, and links to that property ranked across the whole table. All of them are collected under periodic trends.

Niobium electron configuration

The full electron configuration of niobium is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d4 5s1. With the noble-gas core collapsed it is [Kr] 4d4 5s1, and the outermost subshell is 5s1.

Niobium does not follow the simple filling order. Its measured configuration differs from the one the aufbau rule predicts, because its 4d and 5s subshells lie so close in energy that the simple filling order cannot predict which arrangement is lowest. This is a measured fact about the atom rather than an exception to be derived.

Bohr model of niobium (Nb): a nucleus and five shells holding 2, 8, 18, 12 and 1 electrons from the inside out.
Bohr model of niobium (Nb). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.
Orbital box diagram of niobium (Nb), [Kr] 4d4 5s1, with the krypton core drawn as one bar: one box per orbital, filled by Hund’s rule, showing five unpaired electrons, in 4d and 5s.
Orbital diagram of niobium (Nb). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.

Why group and block follow from this is set out in how the periodic table maps electron configuration, and the electron configuration of every element is listed on one page.

Mass of one niobium atom

A molar mass is grams per mole, so dividing by the Avogadro constant gives the mass of a single atom, or for an element with more than one natural isotope the average mass of its atoms, and the reciprocal gives how many atoms sit in a gram.

Mass of one atom

  1. one atom = 92.906 / (6.02214076 × 10²³)
  2. = 1.5427 × 10⁻²² g

Atoms in one gram

  1. atoms per gram = 6.02214076 × 10²³ / 92.906
  2. = 6.4820 × 10²¹ atoms

Niobium on the periodic table

Niobium is in period 5, group 5, in the d-block.

The other elements of group 5 are vanadium, tantalum and dubnium.

The rest of period 5

Work with niobium