LutetiumElectron Configuration, Bohr Model, Valence Electrons & Orbital Diagram

The electron configuration of Lutetium is written as 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f¹⁴ 5d¹ 6s². Applying the Aufbau principle — filling orbitals from lowest to highest energy — plus the Pauli Exclusion Principle and Hund's Rule, we systematically place all 71 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f¹⁴ 5d¹ 6s². Transition metals like Lutetium are defined by d-orbital filling. The five d-orbitals can hold up to 10 electrons and are responsible for Lutetium's characteristic bonding behavior, colored compounds, and catalytic activity.

Lutetium follows the standard Aufbau filling order without exception. The noble gas shorthand [Xe] 4f¹⁴ 5d¹ 6s² replaces the inner-shell electrons with the symbol of the preceding noble gas, highlighting that only the outer electrons — 4f¹⁴ 5d¹ 6s² — are chemically active. Note: for Period 4+ elements, the 4s orbital fills before 3d per Madelung's rule, even though 3d ends at a lower energy in the final atom.

Shell-by-shell, Lutetium's 71 electrons are distributed as: K-shell (n=1): 2 electrons; L-shell (n=2): 8 electrons; M-shell (n=3): 18 electrons; N-shell (n=4): 32 electrons; O-shell (n=5): 9 electrons; P-shell (n=6): 2 electrons. The P-shell (n=6) is the valence shell, containing 3 electrons.

Chemically, this configuration places Lutetium in Group 3 with oxidation states of 3. The partially (or fully) filled d-subshell is the source of Lutetium's variable valency, colored compounds, and catalytic behavior.

The SPDF orbital model describes Lutetium's electrons not as planetary orbits but as three-dimensional probability clouds — each orbital a region of space where an electron is most likely to be found. Lutetium's 71 electrons occupy 14 distinct subshells: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f¹⁴ 5d¹ 6s², governed by three quantum mechanical rules.

The Pauli Exclusion Principle ensures no two electrons in Lutetium share the same four quantum numbers (n, l, m_l, m_s). This is why the 1s orbital holds only 2 electrons, the full p-subshell holds 6, d holds 10, and f holds 14. Without this rule, all 71 electrons would collapse into the 1s orbital. For Lutetium's d-electrons, Hund's Rule requires filling each of the five d-orbitals singly before pairing. This maximizes electron spin, producing Lutetium's characteristic magnetic moment and explaining its tendency toward specific oxidation states.

Following standard orbital filling, Lutetium fills orbitals in the sequence: 1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p → 6s → 4f → 5d → 6p → 7s → 5f → 6d → 7p. The final electron enters the 6s² subshell, making Lutetium a d-block element with 3 valence electrons in Group 3.

The outermost electrons — 6s² — are Lutetium's chemical agents. Understanding the 6s² occupancy — how many electrons, whether paired or unpaired, the orbital shape involved — is the foundation for predicting Lutetium's bonding geometry, oxidation behavior, and compound formation.

Lutetium's chemical reactivity is shaped by three interlocking properties: electronegativity (1.27 Pauling), first ionization energy (5.426 eV), and electron affinity (0.5 eV). Its electronegativity is low-to-moderate (1.27) — predominantly metallic character, electropositive tendency. Lutetium donates electrons to partners rather than accepting them — the hallmark of electropositive metals.

The first ionization energy of 5.426 eV is relatively low, confirming Lutetium's readiness to lose electrons — a quintessentially metallic trait. The electron affinity of 0.5 eV represents the energy released when Lutetium gains one electron, indicating a meaningful but moderate acceptance of electrons.

In standard chemical conditions, Lutetium forms predominantly +3 oxidation state compounds, consistent with its 3 valence electrons and d-block character.

Placing Lutetium between Ytterbium (Z=70) and Hafnium (Z=72) reveals the incremental property changes that make the periodic table a predictive tool.

Ytterbium → Lutetium: adding one proton and one electron increases nuclear charge by 1. Valence electrons remain at 3 — both occupy Group 3. Electronegativity: 1.1 → 1.27 | Ionization energy: 6.254 → 5.426 eV. Atomic radius decreases from 242 pm to 221 pm, consistent with increasing nuclear pull across a period.

Lutetium → Hafnium: the additional proton and electron in Hafnium changes the valence electron count from 3 to 4, crossing from Group 3 to Group 4. This boundary also marks a categorical transition from Lanthanide to Transition Metal. These comparisons confirm that Lutetium sits at a well-defined chemical inflection point in the periodic table.