Atomic number 64

Gadolinium

Gd
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− phase

Shells Orbitals 4f 5d 6s

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64 electrons in 6 shells: 2, 8, 18, 25, 9, 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: 157.25(1) Da
Electron configuration: [Xe] 4f⁷ 5d¹ 6s²
Phase at 25 °C: solid
Melting point: 1312 °C
Boiling point: 3273 °C
Density: 7.90 g/cm³
Electronegativity (Pauling): 1.2
Discovered: 1880, Jean Charles Galissard de Marignac

Neighbours in the table

Eu Tb

Johan Gadolin, a Finnish rare-earth chemist, lent his name to the mineral gadolinite and so to gadolinium, says CIAAW, the atomic-weights commission of IUPAC, chemistry’s world body. In 1880 Jean Charles Galissard de Marignac, a chemist from Switzerland, separated gadolinia, the element’s oxide, Los Alamos reports. His spectra of didymia and gadolinite showed signs of it in the same year, in Jefferson Lab’s account. In CIAAW’s history, his discovery came in 1886, with a white oxide he obtained from samarskite.

Paul-Emile Lecoq de Boisbaudran, a French chemist, named the element in that same year of 1886, according to CIAAW. Los Alamos adds that he isolated gadolinia independently, from the yttria of Mosander.

The silvery-white metal is malleable, ductile and ferromagnetic, according to Los Alamos. At room temperature its atoms pack in a hexagonal close-packed arrangement called the alpha form. In such a lattice, Chem1 notes, every atom sits among 12 nearest neighbours: six beside it and three apiece in the layers above and below. Heated to 1235 °C, alpha gadolinium turns into a beta form with a body-centred cubic structure.

Where it is found

Gadolinium makes up 6.2 milligrams per kilogram of the Earth’s crust and 7 × 10⁻⁷ milligrams per litre of seawater, in Jefferson Lab’s figures. Its namesake mineral, gadolinite, has the formula (Ce,La,Nd,Y)₂FeBe₂Si₂O₁₀. Most gadolinium now comes from monazite and bastnasite, both commercially important ores in Los Alamos’s description.

Seven isotopes make up natural gadolinium, in CIAAW’s 2024 table. Gadolinium-158 is the most common of them at 24.820 per cent, then gadolinium-160 at 21.811 and gadolinium-156 at 20.493. The two isotopes prized for neutron capture, gadolinium-157 and gadolinium-155, supply 15.657 and 14.828 per cent. Gadolinium-154 adds 2.187 per cent and gadolinium-152 just 0.204. That rarest one emits alpha particles with a half-life of 108 trillion years in the evaluation of the International Atomic Energy Agency (IAEA).

The metal can be made by reducing its anhydrous, or water-free, fluoride with calcium metal, according to Los Alamos. Separation by ion exchange and solvent extraction has since greatly improved its availability and lowered its price, Los Alamos adds.

Why it matters

Among all known elements, Los Alamos reports, gadolinium’s thermal neutron capture cross-section is the highest, at 49,000 barns. The cross-section measures how readily its nuclei absorb slow neutrons. The metal can serve in the control rods of nuclear reactors, Jefferson Lab notes. Jefferson Lab says the two isotopes that capture neutrons best, gadolinium-155 and gadolinium-157, are present only in small amounts. As a result, gadolinium control rods lose their effectiveness quickly, and Los Alamos calls the burnout rate very fast.

The same pair of isotopes keeps a record of the Moon’s exposure to neutrons. Gadolinium-157 absorbs neutrons and becomes gadolinium-158, in IUPAC’s isotope notes. Samarium-149 captures neutrons the same way. On a plot of gadolinium-158 and gadolinium-157, each measured against gadolinium-160, a sample’s values move further the longer its exposure. A stronger neutron flux, the stream of neutrons passing through, moves them further too. Lunar samples can therefore be read for their neutron history.

In medicine, gadolinium-153 supplies the photons for dual-photon absorptiometry, a technique that measures bone mineral content, IUPAC reports. Its half-life is 240.6 days in IAEA’s evaluation.

Properties

Properties of gadolinium 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	64
Standard atomic weight	157.25(1) Da	Da	IUPAC/CIAAW 2024
Melting point	1312 °C	°C	Los Alamos: 1312 °C
Boiling point	3273 °C	°C	PubChem: 3546 K
Density	7.90 g/cm³	g/cm³
Electronegativity (Pauling)	1.2
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f⁷ 5d¹
Phase at 25 °C	solid

Safety

The recorded hazards of gadolinium concern fire, and they centre on the finely divided metal. Under the Globally Harmonized System (GHS) of hazard labels it carries the signal word Danger, though 11 of 63 company reports (17.5%) judge it outside the hazard criteria. Of the reports behind that label, 66.7% say it releases flammable gas with water, and 15.9% class it as a flammable solid. The PubChem Laboratory Chemical Safety Summary for gadolinium sets out the classification and handling guidance.

Questions

Is gadolinium magnetic?

Yes. Gadolinium metal is ferromagnetic, and its Curie temperature, the point above which ferromagnetism vanishes, lies just at room temperature, according to Los Alamos. For that reason, Los Alamos suggests, gadolinium could serve as a magnetic component that senses hot and cold.

Is gadolinium used in MRI scans?

Gadolinium-containing compounds are used as contrast agents in magnetic resonance imaging (MRI), in Haz-Map's summary on PubChem, which also links those agents to nephrogenic systemic fibrosis, a condition also called nephrogenic fibrosing dermopathy. The isotope gadolinium-157 has a second medical use: added to neutron capture therapy, it has targeted tumours more effectively than boron-10 on its own, in IUPAC's isotope notes.

Does gadolinium rust in air?

Dry air leaves gadolinium relatively stable, but moist air tarnishes it, Los Alamos reports. The oxide film clings only loosely and falls away, so fresh metal is exposed and oxidation carries on. The metal also reacts slowly with water and dissolves in dilute acid. Los Alamos lists oxidation states of +1, +2 and +3 and describes the oxide as mildly basic.

What else is gadolinium used for?

Gadolinium yttrium garnets serve in microwave applications, and gadolinium compounds have been used as phosphors in colour television sets, Los Alamos reports. Small additions of the metal make iron, chromium and related alloys easier to work and better at resisting heat and oxidation. Gadolinium ethyl sulfate has very low noise and may find use in amplifiers such as the maser. It is also a component of compact discs.