Atomic number 68

Erbium

Er
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Shells Orbitals 4f 6s

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68 electrons in 6 shells: 2, 8, 18, 30, 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: 167.26(1) Da
Electron configuration: [Xe] 4f¹² 6s²
Phase at 25 °C: solid
Melting point: 1529 °C
Boiling point: 2868 °C
Density: 9.07 g/cm³
Electronegativity (Pauling): 1.24
Discovered: 1843, Carl Gustaf Mosander

Neighbours in the table

Ho Tm

Erbium began as the name of a fraction, not of a metal. Carl Gustaf Mosander, a Swedish chemist, split the yttria from the mineral gadolinite into three portions and called them yttria, erbia and terbia. The split dates to 1843 for Jefferson Lab and for CIAAW, the atomic-weights commission of IUPAC (the International Union of Pure and Applied Chemistry). The name comes from Ytterby, the Swedish town where gadolinite was first mined, in CIAAW’s history.

The labels did not stay put. In CIAAW’s history, Mosander’s erbium was a deep-yellow peroxide and his terbium a rose-coloured salt. The change came after 1860 for Mosander’s terbia and after 1877 for the older erbia, in Los Alamos’s dating. The renamed erbia is today’s erbium oxide, Er₂O₃, and it is pink, Jefferson Lab notes.

Urbain and James each isolated fairly pure erbium oxide, Er₂O₃, by 1905. In 1934 Klemm and Bommer obtained reasonably pure metal from the anhydrous chloride, reduced with potassium vapour, Los Alamos reports. The result is soft and malleable, with a bright silvery lustre, and it oxidises more slowly in air than some other rare-earth metals. Inside each erbium atom, six shells take 68 electrons between them, 2, 8, 18, 30, 8 and 2, or [Xe] 4f¹² 6s² in shorthand.

Where it is found

Each kilogram of the Earth’s crust holds an estimated 3.5 milligrams of erbium, and seawater about 8.7 × 10⁻⁷ milligrams per litre, in Jefferson Lab’s figures. Most is recovered by ion exchange from two minerals. One is xenotime, an yttrium phosphate, YPO₄. The other is euxenite, an oxide of niobium, tantalum and titanium that also carries yttrium, calcium, erbium, lanthanum, cerium, uranium and thorium.

Gadolinite, the mineral behind the name, came from a quarry near Ytterby and has yielded a great many rare-earth elements, Jefferson Lab adds. According to Los Alamos, erbium turns up in the same minerals as dysprosium: xenotime, fergusonite, gadolinite, euxenite, polycrase and blomstrandine. Los Alamos’s list for those minerals also names monazite and bastnasite. Ion-exchange methods have cut the prices of rare-earth metals and their compounds sharply in recent years.

Natural erbium is a mix of six stable isotopes, Los Alamos reports. Erbium-166 is the commonest at 33.5 per cent in CIAAW’s abundance figures, ahead of erbium-168 at 27.0 per cent and erbium-167 at 22.9 per cent. Erbium-170 supplies 14.9 per cent, while erbium-164 and erbium-162 together make up less than 2 per cent.

Why it matters

Erbium oxide lends a pink tint, and it has been used to colour glass and porcelain enamel glazes, Los Alamos reports. Many rare-earth salts show pastel colours, linked to their electronic structure, Los Alamos notes. Erbium is a dopant in optical fibre, an impurity added on purpose, where it amplifies the signal, according to Jefferson Lab. Added to vanadium, it makes that metal softer and easier to shape. Erbium also has nuclear uses, Los Alamos and Jefferson Lab report.

Two artificial isotopes of erbium reach medicine, in IUPAC’s isotope notes. Erbium-169, whose half-life is 9.4 days, serves in radiosynovectomy, a radiotherapy for rheumatoid arthritis that has resisted standard treatment. A citrate colloid labelled with this beta emitter is injected into the synovial cavity, inside the synovium, the membrane lining the joint. Cells lining the joint engulf the particles, and the radiation damages the inflamed synovium, halting the inflammation for a time.

Erbium-171, with a half-life of 7.5 hours, has helped researchers follow movement through the bowel. Tablets made with ordinary erbium-170 are irradiated with neutrons, and some of those nuclei capture one to become erbium-171. The tablets are then tracked from outside the body by scintigraphy, imaging of the radiation they give off. Both isotopes decay entirely by beta-minus emission in the evaluation of the International Atomic Energy Agency (IAEA).

Properties

Properties of erbium 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	68
Standard atomic weight	167.26(1) Da	Da	IUPAC/CIAAW 2024
Melting point	1529 °C	°C	Los Alamos: 1529 °C
Boiling point	2868 °C	°C	Los Alamos: 2868 °C
Density	9.07 g/cm³	g/cm³
Electronegativity (Pauling)	1.24
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹²
Phase at 25 °C	solid

Safety

Finely divided erbium metal is flammable, and under the Globally Harmonized System (GHS) of hazard labels it carries the signal word Danger. Most of the 104 company reports to the European Chemicals Agency class it as a flammable solid, while five find that it meets no GHS hazard criteria. Haz-Map ties the fire risk to the fine metal, while Los Alamos calls the metal fairly stable in air. Hazards and handling of the powder are set out in the PubChem Laboratory Chemical Safety Summary for erbium.

Questions

Which elements were discovered in erbia?

The erbia of that era later proved to be five oxides: erbia, scandia, holmia, thulia and ytterbia, according to Los Alamos. Marignac found ytterbia in it in 1878. In 1879 Per Theodor Cleve cleared erbia of every known contaminant and, after further processing, obtained a brown material he named holmia and a green one he named thulia, in Jefferson Lab's account. In 1886 Paul-Émile Lecoq de Boisbaudran found dysprosium as an impurity in erbia, Jefferson Lab reports.

Is erbium radioactive?

Natural erbium is not. Its six isotopes are all stable, according to Los Alamos. Erbium's nuclides and isomers run from erbium-142 to erbium-180, 65 in all, in the table of the Atomic Mass Data Center of the International Atomic Energy Agency (IAEA). Erbium-162 and erbium-170 carry only lower bounds on a half-life there, more than 1.4 × 10¹⁴ and 4.1 × 10¹⁷ years.

What is erbium used for?

Erbium goes into fibre optic cables as a dopant, an impurity introduced on purpose, and works there to amplify the signal, in Jefferson Lab's account on PubChem's record. Mixed into vanadium, it leaves that metal softer and easier to work. It has some roles in the nuclear power industry, and its pink oxide, erbia, colours glass and glazes, Jefferson Lab adds.