63 Eu 151.964

Europium

Lanthanide Europium solid

[Xe] 4f⁷ 6s² · 2 · 8 · 18 · 25 · 8 · 2

← Sm Samarium Gd Gadolinium →

The softest and most reactive lanthanide, and the world's best red phosphor. Europium is the only lanthanide with a stable +2 state, and the security of euro banknotes rests on the switch between +2 and +3.

3D model

Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.

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Atomic properties

Atomic number: 63
Atomic mass: 151.964 а.е.м.
Electron configuration: [Xe] 4f⁷ 6s²
Electrons per shell: 2 · 8 · 18 · 25 · 8 · 2
Block: f-block
Group: no data
Period: 6
Electronegativity (Pauling): 1.2
Electronegativity (Allen): 1.01
Atomic radius: 233 pm
Covalent radius: 198 pm
Van der Waals radius: 233 pm
Ionisation energy 1: 547.1 kJ/mol
Ionisation energy 2: 1 085 kJ/mol
Ionisation energy 3: 2 404 kJ/mol
Ionisation energy 4: 4 120 kJ/mol
Electron affinity: 50 kJ/mol
Common oxidation states: +2, +3
Oxidation states: +2, +3

Physical properties

State at 25 °C: solid
Density: 5.264 g/cm³
Melting point: 1 099 K · 825.9 °C
Boiling point: 1 802 K · 1 528.9 °C
Speed of sound: no data

Thermal properties

Heat of fusion: 9.21 kJ/mol
Heat of vaporisation: 176 kJ/mol
Specific heat capacity: 0.182 J/(g·K)
Thermal conductivity: 13.9 W/(m·K)

Mechanical properties

Young's modulus: 18.2 GPa
Shear modulus: 7.9 GPa
Bulk modulus: 8.3 GPa
Poisson ratio: 0.15
Mohs hardness: no data
Brinell hardness: 167 MPa

Electrical and magnetic properties

Electrical resistivity: 900 nΩ·m
Magnetic ordering: paramagnetic
Curie point: no data
Néel point: no data
Superconducting point: no data

Crystal structure

Crystal structure: body-centred cubic (bcc)
Lattice constants: a = 458.1 pm

Abundance

In the crust: 2 mg/kg
In the ocean: 1.3·10⁻⁷ mg/L
In the universe: 0.05 mg/kg
In the human body: no data

Isotopes

Isotope	Abundance	Half-life	Decay mode
¹⁵¹Eu	47.81 %	4.595·10⁹ Gyr	α
¹⁵³Eu	52.19 %	stable	—

Europium-151 is formally radioactive with a 5·10¹⁸-year alpha half-life — the decay was only detected in 2007.

Discovery

Year of discovery: 1901
Discovered by: Eugène-Anatole Demarçay
Where: France
Origin of the name: named after Europe

History

Eugène Demarçay isolated europium in 1901 from samarium samples after noticing spectral lines belonging to no known element. It was named after the continent.

Where it occurs

2 mg/kg of the crust — one of the rarest lanthanides. Its anomalous depletion or enrichment in a rock, the europium anomaly, is an important geochemical marker.

How it is produced

Separation is easier than for its neighbours because europium is readily reduced to +2 and precipitated as the sulfate, leaving the rest behind.

Role in living things

No biological role.

Safety

Of low toxicity. The metal oxidises readily and ignites in air.

Uses

Red phosphor in picture tubes, fluorescent lamps and white LEDs
Security marks on euro banknotes: under ultraviolet they glow red and green
Reactor control rods
Medical immunoassays using long-lived europium labels

Curiosities

The glow of a euro banknote under ultraviolet is europium complexes at work.
The europium anomaly in lunar rocks helped reconstruct the Moon's magma ocean.
Europium is the only lanthanide soft enough to cut with a knife.
The red of every colour television in the second half of the twentieth century came from europium.