Lutetium (Lu) - Study Guide for JEE/NEET & CBSE

Introduction

Lutetium (Lu) is the last and heaviest element of the lanthanide series, a group of elements often referred to as “rare earth elements.” Despite the name, Lutetium is moderately abundant in the Earth’s crust. Its unique properties, arising from its fully filled 4f subshell, lead to specialized applications primarily in high-technology fields, medical imaging, and targeted radionuclide therapy. Understanding Lutetium’s chemical behavior is crucial for advanced chemistry studies.

CBSE/JEE Quick Revision Notes

• Symbol: Lu
• Atomic Number (Z): 71
• Atomic Mass: 174.967 u (approximately 175 g/mol)
• Block: f-block (classified as a lanthanide, although its ground state electron configuration contains a 5d electron)
• Group: Not formally assigned a group number in the main 1-18 system; considered part of the lanthanide series within Group 3.
• Period: 6
• Valency/Most Common Oxidation State: +3 (highly stable due to 4f¹⁴ configuration)
• Physical State at STP: Solid
• Appearance: Silvery-white, lustrous metal
• Density: 9.84 g/cm³
• Melting Point: 1663 °C
• Boiling Point: 3402 °C
• Nature: Highly electropositive, reactive metal.

Electron Configuration & Bonding Behavior

• Ground State Electron Configuration: [Xe] 4f¹⁴ 5d¹ 6s²
  • The presence of a 5d¹ electron rather than an additional 4f electron makes Lutetium an interesting case often debated for classification. However, it is conventionally grouped with the f-block elements due to its chemical similarity to other lanthanides, the completion of the 4f subshell, and its position immediately after Ytterbium (Yb, 4f¹⁴ 6s²).
• Ionization: Lutetium typically loses its 6s² electrons first, followed by the 5d¹ electron to achieve a highly stable +3 oxidation state.
  • Lu → Lu³⁺ + 3e⁻
  • Electronic Configuration of Lu³⁺: [Xe] 4f¹⁴ (fully filled 4f subshell, which confers significant stability).
• Bonding: Predominantly forms ionic compounds due to its high electropositivity and the stable Lu³⁺ ion.
• Lanthanide Contraction: As the last element of the lanthanide series, Lutetium exhibits the most pronounced effect of lanthanide contraction. The ionic radius of Lu³⁺ is the smallest among the lanthanide ions, significantly impacting the properties of subsequent 5d transition elements (e.g., Hafnium, Hf).

Crucial Chemical Reactions

Lutetium is a reactive metal and its chemical behavior is characteristic of an electropositive lanthanide, primarily forming +3 oxidation state compounds.

1. Reaction with Air/Oxygen: Lutetium tarnishes slowly in moist air but burns readily when heated in oxygen to form lutetium(III) oxide. 4 Lu(s) + 3 O₂(g) → 2 Lu₂O₃(s)

2. Reaction with Water: Reacts slowly with cold water and more vigorously with hot water to form lutetium(III) hydroxide and hydrogen gas. 2 Lu(s) + 6 H₂O(l) → 2 Lu(OH)₃(aq) + 3 H₂(g)

3. Reaction with Acids: Reacts readily with most dilute mineral acids (except hydrofluoric acid, HF, due to insoluble fluoride formation) to form lutetium(III) salts and hydrogen gas. 2 Lu(s) + 6 HCl(aq) → 2 LuCl₃(aq) + 3 H₂(g) 2 Lu(s) + 3 H₂SO₄(aq) → Lu₂(SO₄)₃(aq) + 3 H₂(g)

4. Reaction with Halogens: Lutetium reacts vigorously with all halogens to form lutetium(III) halides. 2 Lu(s) + 3 Cl₂(g) → 2 LuCl₃(s)

Industrial and Biological Importance

Industrial Importance

• Catalysis: Lutetium compounds serve as catalysts in various organic synthesis reactions, including petroleum cracking, alkylation, hydrogenation, and polymerization.
• Medical Imaging (PET Scanners): Lutetium oxyorthosilicate (LSO) and lutetium-yttrium oxyorthosilicate (LYSO) crystals, often doped with cerium, are crucial scintillator materials in Positron Emission Tomography (PET) scanners. Their high density, high light yield, and fast decay time provide excellent spatial resolution and detection efficiency.
• Nuclear Medicine: The radioisotope Lutetium-177 (¹⁷⁷Lu) is a beta-emitting radionuclide used in targeted radionuclide therapy (TRT) for specific cancers, particularly neuroendocrine tumors, in formulations like ¹⁷⁷Lu-DOTATATE. This therapy delivers radiation directly to tumor cells, minimizing damage to healthy tissue.
• Lasers: Lutetium aluminum garnet (LuAG) and lutetium gallium garnet (LGG) are used as host materials for solid-state lasers due to their excellent thermal and optical properties.
• High-Refractive-Index Glass: Lutetium compounds are incorporated into specialized glasses used in optics.

Biological Importance

• Lutetium has no known essential biological role in living organisms.
• In its non-radioactive forms, elemental Lutetium and its compounds are generally considered to have low toxicity.
• The primary biological interaction of Lutetium is through its radioisotope ¹⁷⁷Lu in medical diagnostic and therapeutic applications, where its radioactivity is specifically leveraged.