Nb (Niobium) is an element with position number 41 in the periodic table.
Located in the V period. Melting point: 2468 ℃. Density: 8.58 g/cm^{3}.

The order of filling the orbitals with electrons in the Nb atom is an exception to the rule. Expected electronic configuration 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 4s^{2} 3d^{10} 4p^{6} 5s^{2} 4d^{3} But in reality, one electron moves from the 5s orbital to the 4d orbital:

Electronic configuration of the Niobium atom in ascending order of orbital energies: 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 4s^{2} 3d^{10} 4p^{6} 5s^{1} 4d^{4}

Electronic configuration of the Niobium atom in ascending order of the levels: 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{10} 4s^{2} 4p^{6} 4d^{4} 5s^{1}

Below is the electronic diagram of the Niobium atom
Distribution of electrons over energy levels in the Nb atom 1-st level (K): 2 2-st level (L): 8 3-st level (M): 18 4-st level (N): 12 5-st level (O): 1

Valence electrons of Niobium

The number of valence electrons in a Niobium atom - 5.
Below are their quantum numbers (N - energy, L - angular momentum, M - magnetic moment, S - spin )