65 Tb Terbium 158.925
Lanthanide f-block Period 6

Terbium

Tb · Element 65 · Lanthanide

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A green-phosphor rare earth that also changes shape in a magnetic field.

State at 20°C Solid
Atomic mass 158.925 u
Electron configuration[Xe] 4f⁹ 6s²
64Gd All 118 66Dy

Structure

The terbium atom

Not a diagram of dots on rings — a Monte-Carlo sample of the actual probability density |ψ|² for each occupied subshell. Drag to rotate. Blue and violet mark opposite signs of the wavefunction, which is what makes bonding possible.

Orbital cloud

Measured values

Property sheet

Every bar shows where terbium sits among all 118 elements for that property.

Physical

Density 8.23 g/cm³ 51%
Melting point 1629 K 68%
Boiling point 3503 K 72%
Specific heat 0.182 J/g·K
Thermal conductivity 11.1 W/m·K 30%

Atomic

Atomic radius 176 pm 61%
Covalent radius 194 pm
Van der Waals radius 221 pm

Electronic

Electronegativity 1.2 19%
Ionisation energy 565.4 kJ/mol 18%
Electron affinity 12.7 kJ/mol 15%

Occurrence

Abundance in crust 1.2 mg/kg 51%

Identity

SymbolTb
Atomic number65
Atomic mass158.9254 u
CategoryLanthanide
Blockf
Crystal structurehexagonal close-packed
Oxidation states+3, +4
Discovered1843
Discovered byCarl Gustav Mosander

Sources: IUPAC 2021 standard atomic weights · CRC Handbook of Chemistry and Physics · NIST. Values marked ~ are predicted rather than measured.

Same element, different neutrons

Isotopes of terbium

All terbium atoms have the same number of protons, 65, and differ only in their number of neutrons: those variants are its isotopes. The most common, Tb-159, has 94 neutrons and makes up 100% of natural terbium.

Isotopes of terbium found in nature, with their share of the natural element
ISOTOPE Neutrons Natural Abundance Half-life Decay Mode
Tb-159 most common 94 100% Stable —

Here the classroom shortcut, rounded atomic mass (158.925) minus atomic number, gives the same answer: 94.

Data: IAEA Nuclear Data Section, LiveChart of Nuclides, ground-state evaluations, retrieved October 10, 2026. Abundance is the share of atoms in the natural element; a dash means the isotope has no standard natural abundance.

Size, to scale

How big is a terbium atom?

Radius 176 pm — that is 0.176 nm, so about 2.84 million of them side by side would span a millimetre.

Thermal range

Solid, liquid, gas — and when

Terbium is liquid over a 1874 K window, from 1629 K to 3503 K.

Where it sits

Position in the table

Terbium sits in the lanthanide series, printed below the main grid.

Other lanthanides

57La 58Ce 59Pr 60Nd 61Pm 62Sm 63Eu 64Gd 66Dy 67Ho 68Er 69Tm 70Yb 71Lu
All lanthanides

The story

What terbium is, and how we found it

A green-phosphor rare earth that also changes shape in a magnetic field.

The discovery of terbium

🔬 The Swedish Discovery Story

Discovered by: Carl Gustaf Mosander in Stockholm, Sweden (1843)

Named after: Ytterby, Sweden - the village that gave its name to four different elements

🧪 The Complex Discovery Process

Terbium's discovery represents one of the most challenging achievements in 19th-century analytical chemistry. Carl Gustaf Mosander, working at the Karolinska Institute in Stockholm, began investigating the mineral gadolinite from Ytterby quarry in 1843. This same quarry had already yielded yttrium, but Mosander suspected additional elements remained hidden.

Using chemical precipitation methods, Mosander painstakingly separated the earth then called "yttria" into three distinct components. The process required hundreds of crystallization steps and took nearly two years to complete. He named one of the fractions terbia after the village of Ytterby; the names terbia and erbia were later swapped, and today's terbium comes from his yellow fraction.

⚗️ Verification Challenges

Mosander's discovery faced skepticism from the international scientific community. The chemical properties of terbium were so similar to other rare earths that many scientists questioned whether it was truly a distinct element. Marc Delafontaine's spectroscopic work in the 1860s confirmed the separate elements.

🏆 Scientific Legacy

The village of Ytterby holds the unique distinction of being the source of four element names: yttrium, terbium, erbium, and ytterbium. This small Swedish quarry has contributed more element names than any other location on Earth, making it a pilgrimage site for chemistry enthusiasts worldwide.

🔬 Modern Understanding

Today we know that Mosander's original "terbium" sample contained multiple elements. Terbium was not obtained in pure form until ion-exchange techniques were developed in the mid 20th century. The characteristic brilliant green fluorescence that defines terbium compounds wasn't fully understood until quantum mechanics explained electronic transitions in lanthanide ions.

Terbium's atomic number (65) places it exactly in the middle of the lanthanide series, giving it unique magnetic and optical properties that were completely unknown to its 19th-century discoverers but now drive billion-dollar industries.

Applications

What terbium is used for

Magneto-Optical Technology

Terbium stands as one of the most valuable rare earth elements, commanding premium prices due to its unusual magnetic and optical properties. In the digital age, terbium has become critical for data storage technologies, where its magneto-optical properties enable important advances in computer memory systems.

🔬 Advanced Data Storage Systems

Terbium-based magneto-optical storage materials have transformed digital storage capacity, increasing storage density by 10-15 times compared to conventional systems. These materials form the backbone of next-generation optical storage devices, where terbium's unique ability to change magnetic orientation under laser light creates ultra-high-density data storage solutions.

💡 Energy-Efficient Lighting Technology

In trichromatic fluorescent lamps (energy-saving bulbs), terbium serves as a critical phosphor activator, producing brilliant green emissions at 544 nm wavelength. Combined with europium (red) and cerium (blue), terbium creates the perfect white light spectrum while consuming 75% less energy than incandescent bulbs. Modern LED phosphors increasingly rely on terbium compounds for superior color rendering.

🧲 Ultra-High Performance Permanent Magnets

Terbium additions to neodymium-iron-boron magnets dramatically enhance their temperature stability and coercivity. Even small amounts (2-5%) of terbium can increase operating temperatures from 80°C to over 200°C, making these magnets essential for electric vehicle motors, wind turbine generators, and aerospace applications where high performance is demanded.

🔬 Precision Scientific Instruments

Terbium's exceptional magnetic moment makes it invaluable in magnetostrictive alloys used in sonar systems, actuators, and ultra-precise positioning devices. Terfenol-D (terbium-iron-dysprosium alloy) exhibits the largest room-temperature magnetostriction of any known material, enabling applications in underwater acoustics and vibration control systems.

🏥 Medical Imaging & Diagnostics

Terbium isotopes are studied for nuclear-medicine imaging and therapy, while terbium-activated phosphors in X-ray intensifying screens improve image quality while reducing patient radiation exposure. Advanced terbium compounds are being developed for targeted cancer therapies and diagnostic imaging agents.

🌟 Everyday Applications

  • 🔋 Energy-Saving Light Bulbs: Green phosphor in compact fluorescent lamps (CFLs) and LED lighting systems
  • 💻 Computer Components: Hard drive components and optical storage devices
  • 📱 Smartphone Technology: Speaker magnets and vibration motors in mobile devices
  • 🏠 Home Electronics: High-efficiency motors in appliances and HVAC systems
  • 🎮 Gaming Devices: Precise actuators in gaming controllers and VR equipment
  • 🚗 Automotive Applications: Electric power steering systems and hybrid vehicle components

💰 Market Impact

Despite being one of the most expensive rare earth elements ($800-2000/kg), terbium's exceptional properties make it economically viable for high-value applications. Its scarcity drives innovation in recycling technologies and alternative material research.

🔬 Research Frontiers

Emerging applications include quantum computing components, advanced photonic devices, and next-generation solid-state lighting. Scientists are exploring terbium-based single-molecule magnets for ultra-high-density data storage and quantum information processing.

Where it comes from

Natural occurrence

1.2 mg/kg of Earth's crust · more abundant than 51% of elements

🌍 Global Distribution & Mining

Terbium represents one of the least abundant rare earth elements in Earth's crust, with an average concentration of only 1.2 parts per million. This scarcity, combined with complex extraction processes, makes terbium one of the most valuable rare earth commodities.

🏔️ Primary Mineral Sources

  • Bastnäsite: Primary commercial source, found in carbonatite deposits
  • Monazite: Beach sand mineral containing 0.03% terbium oxide
  • Xenotime: Heavy rare earth phosphate mineral in alluvial deposits
  • Ion-adsorption clays: Southern China deposits with enhanced heavy REE content

🌏 Major Global Deposits

China (about 69% of the world's rare-earth mine output in 2025): Bayan Obo mine in Inner Mongolia produces most commercial terbium. Southern China's ion-adsorption clay deposits in Jiangxi and Guangdong provinces are particularly rich in heavy rare earths including terbium.

Australia: Mount Weld deposit contains significant terbium reserves within its bastnäsite ore body. Lynas Corporation processes this ore at their Malaysian facility.

United States: Mountain Pass mine in California and Bear Lodge project in Wyoming contain terbium-bearing bastnäsite deposits.

⚒️ Extraction & Processing

Terbium extraction requires sophisticated multi-stage separation processes due to the chemical similarity of lanthanides. Ion-exchange chromatography and solvent extraction using specific chelating agents can separate terbium from other rare earths. The final purification often requires hundreds of separation stages to achieve 99.9% purity.

♻️ Recycling Potential

Given terbium's high value and scarcity, recycling from permanent magnets and phosphors is increasingly important. Advanced hydrometallurgical processes can recover terbium from end-of-life products, though current recycling rates remain below 5% globally.

Handling

Safety

⚠️ Handling & Safety Protocols

🟡 Moderate Hazard Classification

Terbium metal and its compounds present moderate safety risks requiring standard laboratory precautions. While not highly toxic, proper handling procedures must be followed to prevent exposure and ensure safe laboratory practices.

🥽 Personal Protective Equipment

  • Eye Protection: Safety glasses or goggles required for all handling
  • Respiratory Protection: Dust mask or respirator when working with powders
  • Hand Protection: Nitrile or neoprene gloves to prevent skin contact
  • Body Protection: Laboratory coat and closed-toe shoes mandatory

⚗️ Chemical Hazards

Fire Risk: Terbium metal powder is pyrophoric and may ignite spontaneously in air. Store under inert atmosphere (argon or nitrogen) and keep away from oxidizing agents.

Dust Inhalation: Terbium oxide dust may cause respiratory irritation. Work in well-ventilated areas or use fume hoods when handling powdered compounds.

🏥 First Aid Procedures

  • Eye Contact: Flush immediately with water for 15 minutes, seek medical attention
  • Skin Contact: Wash thoroughly with soap and water, remove contaminated clothing
  • Inhalation: Move to fresh air immediately, monitor for respiratory distress
  • Ingestion: Rinse mouth, do not induce vomiting, seek immediate medical care

🗄️ Storage Requirements

Store terbium compounds in tightly sealed containers in cool, dry conditions. Metal powders require inert atmosphere storage to prevent oxidation. Keep away from strong acids, bases, and oxidizing materials.

♻️ Waste Disposal

Terbium-containing waste must be collected separately for recycling due to its high value and scarcity. Follow institutional waste disposal procedures for rare earth materials.

Keep exploring

Use terbium in the tools

Quick answers

Terbium: common questions

What is terbium?

Terbium (symbol Tb) is element 65 on the periodic table, a lanthanide in period 6. A green-phosphor rare earth that also changes shape in a magnetic field. At room temperature it is a solid.

What is the electron configuration of terbium?

Terbium's ground-state electron configuration is [Xe] 4f⁹ 6s², giving 6 occupied shells with the distribution 2, 8, 18, 27, 8, 2.

What are the melting and boiling points of terbium?

Terbium melts at 1629 K (1355.9 °C) and boils at 3503 K (3229.9 °C).

What is the atomic mass of terbium?

The standard atomic weight of terbium is 158.925 u. That is a weighted average across its naturally occurring isotopes, which is why it is rarely a whole number.

How many neutrons does terbium have?

The most common terbium atom, Tb-159, has 94 neutrons: its mass number, 159, minus its atomic number, 65. It makes up 100% of natural terbium. The classroom shortcut, rounded atomic mass (158.925) minus atomic number, gives the same 94.

How dense is terbium?

Terbium has a density of 8.23 g/cm³. Water is 1.0 g/cm³, so a block of terbium is about 8.2× heavier.

What is the electronegativity of terbium?

Terbium has a Pauling electronegativity of 1.2. The scale runs from 0.70 (francium, the least greedy for electrons) to 3.98 (fluorine, the most). A value this low means it readily gives its outer electrons away, forming positive ions.

Who discovered terbium, and when?

Terbium was discovered in 1843 by Carl Gustav Mosander. Origin of the name: Ytterby, Sweden.

How common is terbium on Earth?

Terbium makes up about 1.2 mg/kg of the Earth's crust — uncommon, but not rare.

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