Atomic number 63

Europium

Eu
+ phase
− phase

Shells Orbitals 4f 6s

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63 electrons in 6 shells: 2, 8, 18, 25, 8, 2.

Shells are a teaching model: an electron does not travel on a ring at a fixed distance.

Category: Lanthanide
Period: 6
Block: f
Standard atomic weight: 151.96(1) Da
Electron configuration: [Xe] 4f⁷ 6s²
Phase at 25 °C: solid
Melting point: 826 °C
Boiling point: 1529 °C
Density: 5.24 g/cm³
Discovered: 1896, Eugène-Anatole Demarçay

Neighbours in the table

Sm Gd

In 1890 Boisbaudran obtained fractions from samarium and gadolinium concentrates whose spark spectra showed lines neither element explained, Los Alamos records, and those lines were later traced to europium. Eugène-Anatole Demarçay, a chemist from France, suspected an unknown contaminant in samarium. He separated it from magnesium samarium nitrate in 1896, in the history by CIAAW, the atomic-weights commission of IUPAC (the International Union of Pure and Applied Chemistry). The same history traces the name to the continent of Europe.

By 1901 Demarçay had europium in reasonably pure form, Jefferson Lab notes, and Los Alamos credits the discovery to that separation. Europium, [Xe] 4f⁷ 6s², has 63 electrons, 2, 8, 18, 25, 8 and 2 per shell. Jefferson Lab lists +3 and +2 as its oxidation states, and Los Alamos adds +1. Each is the charge an atom would carry if its more electronegative partner took all the bonding electrons, in Chem1’s account.

Among the rare-earth metals, Los Alamos ranks europium as the most reactive: it oxidises quickly in air and reacts with water much as calcium does. It is about as hard as lead and quite ductile. In Stephen Lower’s Chem1 account, each ion in a metal sits in a fluid of electrons on every side. The bonding therefore has no preferred direction, which accounts for a metal’s ductility.

Where it is found

Europium makes up 2.0 milligrams of each kilogram of the Earth’s crust, and seawater carries 1.3 × 10⁻⁷ milligrams per litre, according to Jefferson Lab. Bastnasite and monazite are its principal ores, Los Alamos reports. Today most europium comes out of monazite sand, a phosphate rich in rare-earth elements, by ion exchange. Spectra have also picked out europium in the Sun and in certain stars.

Natural europium is a mixture of two isotopes: europium-151, at 47.81 per cent, and europium-153, at 52.19 per cent, in CIAAW’s figures. Europium-151 is not quite stable. It emits alpha particles with a half-life of 4.6 × 10¹⁸ years in the evaluation of the International Atomic Energy Agency (IAEA), while europium-153 is listed as stable.

The metal is now made by heating europium oxide, Eu₂O₃, with lanthanum metal under high vacuum, in Los Alamos’s account. The europium collects as a silvery-white deposit on the walls of the crucible. Ion-exchange and other special processes have greatly cut the metal’s cost in recent years. Behind it all lies rare-earth mining, an estimated 390,000 tons of oxide equivalent worldwide in 2024, the US Geological Survey reports.

Why it matters

Jefferson Lab describes Eu₂O₃ as a widely used red phosphor, a substance that glows when struck by electrons or light, for television sets. It also acts as an activator in phosphors based on yttrium. The metal itself has no commercial applications, though it has been used to dope plastics that serve as lasers, adding a small amount of it to them. The US Geological Survey priced europium oxide of at least 99.99 per cent purity at 31 dollars a kilogram in 2020 and an estimated 27 in 2024.

Europium-152 forms when europium-151 captures a neutron, in IUPAC’s isotope notes on PubChem’s record. Europium-152, with a half-life of 13.517 years, and europium-154, with 8.592 years, serve as reference sources for calibrating gamma-ray spectrometers.

The same pair dates river mud. Discharges from the Krasnoyarsk reactors left europium-152 and europium-154 in the Yenisei River, alongside caesium-137 and cobalt-60. IUPAC notes that the ratio of europium-154 to europium-152 falls with depth, and that decline gives the age of bottom sediments and floodlands.

Europium isotopes absorb neutrons well. IUPAC says they have been used in nuclear control applications, while Jefferson Lab describes them as under study for reactors. Fast neutrons striking europium-153 can also produce samarium-153, a therapeutic radionuclide, or radioactive isotope, whose half-life is about 1.9 days.

Properties

Properties of europium Standard atomic weights from IUPAC/CIAAW (abridged, 2024); other values from PubChem's periodic table, kelvin converted to °C.
Property	Value	Unit	Source
Atomic number	63
Standard atomic weight	151.96(1) Da	Da	IUPAC/CIAAW 2024
Melting point	826 °C	°C	Los Alamos: 826 °C
Boiling point	1529 °C	°C	Los Alamos: 1529 °C
Density	5.24 g/cm³	g/cm³
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f⁷
Phase at 25 °C	solid

Safety

Europium metal can catch fire by itself in air, and the Globally Harmonized System (GHS) of hazard labels gives it the signal word Danger. Of 48 company reports behind that classification, 83.3% describe spontaneous ignition in air, 12.5% a flammable solid and 10.4% flammable gas released on contact with water. Los Alamos gives an ignition temperature in air of roughly 150 to 180 °C. For anyone handling the metal, the PubChem Laboratory Chemical Safety Summary for europium sets out the precautions.

Questions

Why is europium named after Europe?

Its name derives from the continent of Europe, in the history by CIAAW, IUPAC's atomic-weights commission, on PubChem's record. In 1890 Boisbaudran found unexplained spark lines in fractions from samarium-gadolinium concentrates, lines later shown to be europium's. Eugène-Anatole Demarçay, working in France, separated it from samarium in 1896 and had it reasonably pure by 1901.

Is europium radioactive?

Natural europium is slightly radioactive. Of its two natural isotopes, europium-151 makes up 47.81 per cent and alpha-decays with a half-life of 4.6 × 10¹⁸ years, in the International Atomic Energy Agency's evaluation. Europium-153, the other 52.19 per cent, is listed as stable. Reactors also make europium-152 and europium-154, with half-lives of 13.517 and 8.592 years.

Does europium react with water?

It does, and Los Alamos compares the reaction with that of calcium. The same page ranks europium first for reactivity among the rare-earth metals; it oxidises quickly and ignites in air somewhere between about 150 and 180 °C. About one in ten of the company reports behind its hazard classification adds that it releases flammable gases on contact with water, which may ignite by themselves.

What is europium oxide used for?

Jefferson Lab, in PubChem's record, describes europium oxide, Eu₂O₃, as a widely used red phosphor, a substance that glows when struck by electrons or light, for television sets. It is also added as an activator to phosphors built on yttrium. In 2024 the pure oxide cost an estimated 27 dollars a kilogram, in US Geological Survey figures.