57 La Lanthanum 138.905
Lanthanide f-block Period 6

Lanthanum

La · Element 57

The first lanthanide and the element that hid inside cerium for 36 years before anyone noticed.

STATE AT 20°C Solid
ATOMIC MASS 138.905 u
ELECTRON CONFIGURATION [Xe] 5d¹ 6s²
56Ba All 118 58Ce

Structure

The lanthanum 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 lanthanum sits among all 118 elements for that property.

Physical

Density 6.162 g/cm³ 35%
Melting point 1193 K 52%
Boiling point 3737 K 80%
Specific heat 0.195 J/g·K
Thermal conductivity 13.4 W/m·K 41%

Atomic

Atomic radius 187 pm 74%
Covalent radius 207 pm
Van der Waals radius 240 pm

Electronic

Electronegativity 1.1 10%
Ionisation energy 538.4 kJ/mol 12%
Electron affinity 48.2 kJ/mol 31%

Occurrence

Abundance in crust 39 mg/kg 77%

Identity

SymbolLa
Atomic number57
Atomic mass138.9055 u
CategoryLanthanide
Blockf
Crystal structurehexagonal
Oxidation states+2, +3
Discovered1839
Discovered byCarl Gustav Mosander

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

Size, to scale

How big is a lanthanum atom?

Radius 187 pm — that is 0.187 nm, so about 2674 million of them side by side would span a millimetre.

Thermal range

Solid, liquid, gas — and when

Lanthanum is liquid over a 2544 K window, from 1193 K to 3737 K.

Where it sits

Position in the table

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

OTHER LANTHANIDES

58Ce 59Pr 60Nd 61Pm 62Sm 63Eu 64Gd 65Tb 66Dy 67Ho 68Er 69Tm 70Yb 71Lu
All lanthanides

The story

What lanthanum is, and how we found it

The first lanthanide and the element that hid inside cerium for 36 years before anyone noticed.

The discovery of lanthanum

The Discovery Saga

1839 - The First Clue

Carl Gustav Mosander, a Swedish chemist and student of the great Jöns Jakob Berzelius, was studying cerium nitrate when he noticed something peculiar. The supposedly pure cerium exhibited properties that didn't quite match what was expected.

The Separation Triumph

Through meticulous fractional crystallization - a painstaking process of repeatedly dissolving and recrystallizing compounds - Mosander managed to separate what he thought was pure cerium into two distinct substances.

Naming the Element

Mosander named the new element "lanthanum" from the Greek word "lanthanein," meaning "to lie hidden". This was incredibly prophetic - lanthanum had indeed been hiding in cerium samples for decades.

Historical Context

Mosander's discovery came during the golden age of elemental discovery. The same year (1839), he also discovered terbium and erbium. His systematic approach to separating rare earth elements laid the groundwork for understanding the entire lanthanide series.

"The elements seemed to multiply before our eyes, each separation revealing new complexities hidden within what we thought was simple."

— Contemporary description of rare earth element discoveries

Scientific Impact

Mosander's discovery of lanthanum was significant because it proved that even "well-known" elements could harbor hidden secrets. This discovery sparked a 70-year quest to separate and identify all the rare earth elements, fundamentally changing our understanding of atomic structure and periodicity.

Mosander's Legacy

Carl Mosander discovered more elements than any other scientist except for Glenn T. Seaborg. His methodical approach to rare earth separation influenced generations of chemists and established Sweden as a powerhouse in early elemental chemistry.

Applications

What lanthanum is used for

Advanced Industrial Applications

Lanthanum is the gateway element to the lanthanide series and plays crucial roles in modern technology. As a catalyst extraordinaire, lanthanum compounds are essential in petroleum refining, where they help crack heavy crude oil into gasoline and diesel fuel that powers our world.

Camera Revolution

High-end camera lenses contain lanthanum glass - up to 50% by weight. This special glass has an incredibly low dispersion, meaning it bends different colors of light by almost the same amount, eliminating the rainbow fringes (chromatic aberration) that plague cheaper lenses. When you see those crystal-clear, professional photographs, lanthanum is working behind the scenes.

Battery Technology

Nickel-metal hydride (NiMH) batteries - found in hybrid cars like the Toyota Prius - rely on lanthanum-based alloys to store hydrogen. A typical hybrid car battery contains about 10-15 kg of lanthanum, making it one of the largest industrial uses of this rare earth element.

Lighter Flints & Spark Generation

The "flint" in cigarette lighters is actually a mischmetal alloy containing 25-50% lanthanum. When struck, lanthanum creates the bright sparks that ignite the fuel. This same technology is used in welding electrodes and theatrical pyrotechnics.

Advanced Materials

  • Hydrogen storage materials for fuel cell research
  • Superconducting materials when combined with copper and oxygen
  • Phosphor materials for energy-efficient lighting
  • Ceramic capacitors for electronic devices

Everyday Applications

Automotive

  • Hybrid vehicle batteries (Toyota Prius, Honda Insight)
  • Catalytic converters for emission control
  • High-performance headlight glass
  • Fuel additives for cleaner burning

Optics & Photography

  • Professional camera lenses (Canon, Nikon telephoto lenses)
  • Telescope mirrors and lenses
  • Binocular and microscope optics
  • Virtual reality headset lenses

Lighting Technology

  • Carbon arc lighting for movie projectors
  • Studio lighting equipment
  • Energy-efficient fluorescent bulbs
  • LED phosphor coatings

Tools & Equipment

  • Disposable cigarette lighters
  • Welding electrode coatings
  • Spark plug materials
  • Laboratory equipment

Where it comes from

Natural occurrence

39 mg/kg of Earth's crust · more abundant than 77% of elements

Natural Distribution

Despite being called "rare earth," lanthanum is actually three times more abundant than lead in Earth's crust. The "rare" designation comes from the extreme difficulty of separating and purifying these elements from their natural state.

Abundance Statistics

  • Earth's Crust: 39 parts per million (ppm)
  • Ranking: 28th most abundant element
  • Ocean Water: 3.4 × 10⁻⁶ ppm
  • Universe: Extremely rare, formed in stellar nucleosynthesis

Primary Mineral Sources

Bastnäsite

Chemical formula: (Ce,La)CO₃F
La content: 25-35%
Major deposits: Mountain Pass (California), Bayan Obo (China)

Monazite

Chemical formula: (Ce,La,Nd,Th)PO₄
La content: 15-25%
Major deposits: Australia, India, Brazil, South Africa

Global Distribution

  • China: 85% of world production (Inner Mongolia)
  • United States: Mountain Pass mine (recently reopened)
  • Australia: Mount Weld deposit
  • India: Kerala and Tamil Nadu beach sands
  • Brazil: Minas Gerais state deposits

Geological Formation

Lanthanum forms through fractional crystallization in alkaline igneous rocks and carbonatites. It concentrates in late-stage magmatic processes and weathering products, often associated with fluorine and carbonate minerals.

Handling

Safety

Safety Information

Moderate Hazard Level

Lanthanum and its compounds are generally considered moderately hazardous with specific precautions required for safe handling.

Respiratory Concerns

Inhalation Risk: Lanthanum dust can cause respiratory irritation and potential lung damage. Fine particles may cause pneumoconiosis (lung scarring) with prolonged exposure.

  • Use appropriate dust masks (N95 minimum) when handling powders
  • Ensure adequate ventilation in work areas
  • Avoid creating airborne dust through grinding or cutting

Eye and Skin Contact

  • Eye Contact: Can cause irritation and possible corneal damage
  • Skin Contact: May cause dermatitis in sensitive individuals
  • PPE Required: Safety glasses and chemical-resistant gloves

First Aid Procedures

Inhalation

Move victim to fresh air immediately. If breathing difficulties persist, seek medical attention.

Eye Contact

Flush with clean water for 15 minutes. Remove contact lenses if easily removable. Seek medical attention.

Skin Contact

Wash affected area with soap and water. Remove contaminated clothing.

Ingestion

Rinse mouth with water. Do not induce vomiting. Seek immediate medical attention.

Storage Requirements

  • Store in cool, dry area away from strong acids
  • Keep containers tightly sealed to prevent oxidation
  • Separate from incompatible materials (strong oxidizers)
  • Use corrosion-resistant containers for compounds

Environmental Considerations

Lanthanum compounds should not be released into waterways as they can bioaccumulate in aquatic organisms. Dispose of waste through licensed hazardous waste facilities.

Quick answers

Lanthanum: common questions

What is Lanthanum?

Lanthanum (symbol La) is element 57 on the periodic table, a lanthanide in period 6. The first lanthanide and the element that hid inside cerium for 36 years before anyone noticed. At room temperature it is a solid.

What is the electron configuration of Lanthanum?

Lanthanum's ground-state electron configuration is [Xe] 5d¹ 6s², giving 6 occupied shells holding 2, 8, 18, 18, 9, 2 electrons respectively.

What are the melting and boiling points of Lanthanum?

Lanthanum melts at 1193 K (919.9 °C) and boils at 3737 K (3463.9 °C).

What is the atomic mass of Lanthanum?

The standard atomic weight of Lanthanum is 138.905 u. That is a weighted average across its naturally occurring isotopes, which is why it is rarely a whole number.

How dense is Lanthanum?

Lanthanum has a density of 6.162 g/cm³. Water is 1.0 g/cm³, so a block of lanthanum is about 6.2× heavier.

What is the electronegativity of Lanthanum?

Lanthanum has a Pauling electronegativity of 1.1. 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 Lanthanum, and when?

Lanthanum was discovered in 1839 by Carl Gustav Mosander. It is named after greek lanthanein, "to lie hidden".

How common is Lanthanum on Earth?

Lanthanum makes up about 39 mg/kg of the Earth's crust — uncommon, but not rare.

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