Numford
Electronic configuration

Niobium (Nb)

[Kr] 4d⁴ 5s¹, an exception. 5 unpaired electrons, period 5, group 5, d block.

Element or ion

Type a symbol, a name or an atomic number, add a charge such as Fe3+ or Cl-, or tap an element in the table. Orbitals fill from m = −l up, spin +½ first.

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H1He2Li3Be4B5C6N7O8F9Ne10Na11Mg12Al13Si14P15S16Cl17Ar18K19Ca20Sc21Ti22V23Cr24Mn25Fe26Co27Ni28Cu29Zn30Ga31Ge32As33Se34Br35Kr36Rb37Sr38Y39Zr40Nb41Mo42Tc43Ru44Rh45Pd46Ag47Cd48In49Sn50Sb51Te52I53Xe54Cs55Ba56Hf72Ta73W74Re75Os76Ir77Pt78Au79Hg80Tl81Pb82Bi83Po84At85Rn86

NbNiobium, Z = 41, 92.906 u

[Kr] 4d4 5s1

In full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d⁴ 5s¹

[Kr]4d5s
  • Blockd block
  • Period5
  • Group5
  • Valence5
  • Unpaired5
  • MagneticPara

Last electron 4d

  • n4shell
  • l2d subshell
  • m+1orbital
  • s+½spin up
Why Nb is an exception

Plain filling would give [Kr] 4d³ 5s². For heavier atoms the (n − 1)d, (n − 2)f and ns levels lie very close together, so one electron sits in d. These are the configurations found by experiment and printed in the NCERT tables.

Working

Step by step

  1. Niobium has 41 electrons.
  2. Fill in (n + l) order: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d³.
  3. That gives [Kr] 4d³ 5s², but the accepted configuration is [Kr] 4d⁴ 5s¹. For heavier atoms the (n − 1)d, (n − 2)f and ns levels lie very close together, so one electron sits in d. These are the configurations found by experiment and printed in the NCERT tables.
  4. Write the subshells in order of n: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d⁴ 5s¹.
  5. Replace the krypton core with [Kr]: [Kr] 4d⁴ 5s¹.
At a glance

Niobium (Nb): the numbers

Atomic number41
Atomic mass92.906 u
Period5
Group5
Blockd block
Valence electrons5
Unpaired electrons5
Magneticparamagnetic
Last electron4d: n = 4, l = 2, m = +1, s = +1/2
Questions

Niobium (Nb): quick answers

What is the electronic configuration of niobium?

Niobium has 41 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d⁴ 5s¹, or [Kr] 4d⁴ 5s¹ in short.

Why is niobium [Kr] 4d⁴ 5s¹ and not [Kr] 4d³ 5s²?

For heavier atoms the (n − 1)d, (n − 2)f and ns levels lie very close together, so one electron sits in d. These are the configurations found by experiment and printed in the NCERT tables.

What are the quantum numbers of the last electron of niobium?

The last electron goes into 4d: n = 4, l = 2, m = +1, s = +1/2. Orbitals fill from m = −l up, spin +½ first.

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