Gadolinium

Gadolinium
Atomic number	64
Symbol	Gd
Group	Lanthanides
Boiling point	3000 °C
Electron configuration	[Xe] 4f7 5d1 6s2
Density	7.90 g/cm^3
Period	6
Melting point	1312 °C
Phase STP	Solid
Block	f
Oxidation states	+3, +2
Wikidata	Q1832

Gadolinium (symbol Gd, atomic number 64) is a silvery-white metal in the lanthanide series of rare-earth elements (atomic numbers 57–71). It is a malleable, ductile solid (phase at STP) that slowly oxidizes in air. The most common oxidation state of gadolinium is +3 (Gd³⁺), as found in its salts and compounds. Its standard atomic weight is about 157.25. Gadolin­ium’s notable properties include a very large neutron-capture cross-section (especially for isotope Gd-157) and unique magnetic behavior (ferromagnetic below ≈20 °C, strongly paramagnetic at or above room temperature). Because free Gd³⁺ ions are toxic to organisms, gadolinium is handled and used primarily in chemically bound (chelated) form in applications such as medical MRI contrast agents.

Gadolinium appears between europium (Eu) and terbium (Tb) in the periodic table, period 6, and is an f-block element (sometimes placed in “group 3” in older tables, but more properly in the lanthanide series). It has an electron configuration [Xe]4f⁷5d¹6s² with seven electrons in the 4f shell. This half-filled f-shell gives gadolinium unusually high magnetic moment when in the +3 state. At room temperature gadolinium metal is paramagnetic – it becomes ferromagnetic only below its Curie temperature of about 293 K (20 °C). Gadolinium does not occur on Earth as a pure element; it is found in trace amounts in minerals that contain other rare earth elements.

Key facts and identifiers for gadolinium include: atomic number 64, standard atomic weight 157.25, block f, period 6, principal oxidation state +3, electronegativity ≈1.20 (Pauling), first ionization energy ≈594 kJ/mol (6.15 eV), and density about 7.90 g/cm³. Its electrical resistivity at 20 °C is roughly 1.3×10⁻⁶ Ω·m, and its thermal conductivity is around 10.6 W·m⁻¹·K⁻¹ at 300 K. In its pure form, gadolinium has a hexagonal close-packed (hcp) crystal structure at room temperature (the α phase) and transforms to a body-centered cubic (bcc) β phase at higher temperature (~1235 °C).

Atomic Structure and Electron Configuration

Gadolinium’s 64 electrons occupy electron shells around the nucleus in the pattern 2, 8, 18, 25, 9, 2. Its ground-state electron configuration is [Xe]4f⁷5d¹6s². In other words, gadolinium has a xenon core plus seven 4f-electrons, one 5d-electron, and two 6s-electrons. The seven 4f-electrons are significant: they form a half-filled subshell that is relatively stable. The valence shell (outer shell) electrons are the 4f, 5d, and 6s electrons, of which three (one 5d and two 6s) are most easily removed to form ions.

In compounds, gadolinium almost always loses three electrons to become Gd³⁺. The remaining 4f-electrons on Gd³⁺ are still present but are core-like and contribute to gadolinium’s magnetic moment (each takes one unpaired spin). The Gd³⁺ ion, with configuration [Xe]4f⁷, has seven unpaired 4f-electrons and thus a high total spin (S = 7/2). This high spin state is why Gd³⁺ exhibits exceptionally strong paramagnetism (alignment with an applied magnetic field) above its Curie point, and ferromagnetism below it.

Across the periodic table, gadolinium follows the expected lanthanide trends. Its atomic radius (empirical) is about 180 picometers (pm), similar to or slightly smaller than its neighbor terbium (Tb) due to the lanthanide contraction. The Pauling electronegativity of gadolinium is about 1.20 (a low value, reflecting its electropositive character), and its first ionization energy is relatively modest (~6.15 eV, or ~594 kJ/mol). The second and third ionization energies are higher (each above 11 eV) reflecting the removal of the two 6s and the 5d electron. These values—low electronegativity and ionization energy—mean gadolinium readily forms Gd³⁺ by losing its outer electrons, consistent with its chemistry.

Thus, gadolinium is a fairly large, electropositive atom with a half-filled 4f shell. The half-filled configuration provides extra stability; for example, the Gd atom has a lower-than-expected ionization energy compared to adjacent lanthanides because removing the stable half-filled f-electron would require more energy, so ironically Gd’s first ionization energy is actually lower than its neighbor europium’s. This behavior underlies some of the subtleties of lanthanide chemistry but in practice Gd behaves like most trivalent lanthanoid metals.

Isotopes and Nuclear Properties

Naturally occurring gadolinium consists of several isotopes. There are six stable isotopes: ^154Gd, ^155Gd, ^156Gd, ^157Gd, ^158Gd, and ^160Gd. The most abundant is ^158Gd (about 24.8% of natural Gd). Additionally, ^152Gd is a trace isotope that undergoes extremely slow alpha decay (half-life ~1×10^14 years), so it is often counted as a long-lived radioisotope. All other isotopes of gadolinium are radioactive, with half-lives typically much shorter (days to years). For example, ^153Gd (t₁/₂ ≈ 241 days) is an artificial radioisotope commonly produced in nuclear reactors; it decays by electron capture and emits X-rays/gamma rays. ^148Gd (t₁/₂ ≈ 86 years) and ^150Gd (t₁/₂ ≈ 1.79×10^6 years) are long-lived alpha and beta emitters of interest in nuclear studies. In total, over thirty Gd radioisotopes have been observed, but most have half-lives under a minute. Gadolinium also has some meta-stable nuclear isomers (excited states), the longest of which have lifetimes on the order of minutes.

A striking property of gadolinium isotopes is their neutron-capture cross section. ^157Gd has the highest known thermal-neutron capture cross-section of any stable nuclide – about 2.6×10^5 barns (barn = 10^-28 m²). ^155Gd also has a very high cross-section (~6×10^4 barns). (By comparison, a typical absorber like ^235U is only ~98 barns.) This “giant” cross section arises from quantum absorption resonances in the Gd nucleus. Because of this, Gd is exceptionally good at absorbing slow (thermal) neutrons. This property is exploited in nuclear reactors (for control rods and shielding) and in neutrino-detection experiments (adding gadolinium to water greatly increases neutron capture signals). The neutron absorption is sometimes used medically in experimental neutron-capture therapy for cancer, where Gd compounds are introduced to tumor tissue and irradiated with neutrons to induce local radiation.

Gadolinium’s nuclear spins are relevant to magnetic resonance as well. The stable odd-A isotopes ^155Gd and ^157Gd have nuclear spin 3/2 (in their ground states). However, nuclear magnetic resonance (NMR) of these isotopes is not commonly used for chemical analysis, because the very large nuclear quadrupole moment and strong paramagnetism of Gd³⁺ broaden the signals. Instead, Gd³⁺ is often used as a contrast agent in electron paramagnetic resonance (EPR/ESR) and in magnetic resonance imaging (MRI) via its effect on nearby water proton relaxation.

In summary, gadolinium has multiple stable isotopes, a variety of radioisotopes, and is distinguished by extremely high neutron-capture ability (especially as Gd-157). These nuclear properties underlie its use in nuclear technology and in research.

Allotropes and Typical Compounds

Gadolinium has no allotropes in the sense that nonmetals like carbon do (no distinct atomic/molecular forms). However, the metallic form of gadolinium exists in two crystal phases. At room temperature it is the α-phase with a hexagonal close-packed (hcp) structure. When heated above about 1235 °C, it transforms into a β-phase with a body-centered cubic (bcc) lattice. These are merely different stacking arrangements of Gd atoms and do not create new chemical behavior, but engineers note the change because it slightly alters the metal’s density and properties at high temperature.

Chemically, gadolinium behaves like a typical trivalent lanthanide. Its stable compounds almost always involve Gd³⁺. Gadolinium(III) oxide, Gd₂O₃, is the principal oxide: a white, refractory solid (high melting point ~2330 °C). This oxide is basic and insoluble in water; it dissolves only in strong acids to make gadolinium(III) salts. Gd₂O₃ and related compounds (such as hydroxide Gd(OH)₃) are used in ceramics or as precursors to other materials.

Important simple compounds include the halides GdF₃, GdCl₃, GdBr₃, and GdI₃, made by direct reaction of Gd metal with halogens or by acid dissolution of Gd₂O₃. These are ionic solids (salts) with gadolinium in the +3 state. For example, GdCl₃ is often used to prepare other gadolinium chemicals. Gadolinium also forms chalcogenides like Gd₂S₃ and nitrides such as GdN. GdN is notable as a ferromagnetic semiconductor (Curie ~65 K). Hydrides are known too: gadolinium reacts with hydrogen under pressure to yield GdH₂ and the trihydride GdH₃. The dihydride is metallic, while GdH₃ is less conducting.

Because the Gd³⁺ ion is large and electropositive, Gd compounds often have high coordination numbers (8 or 9). In solution, Gd³⁺ behaves as a hard acid and forms complexes with ligands like water, carbonate, or chelators. Chelating agents (multidentate ligands) can encapsulate Gd³⁺ tightly; common examples are DTPA (diethylenetriaminepentaacetate) or DOTA, used in MRI contrast agents. There are no simple organic Gd compounds of importance, but a wide variety of coordination complexes exists for research.

In alloys, adding a small percentage of Gd improves high-temperature strength and corrosion resistance of steels and other metals. Gadolinium also alloys with transition metals; for example, GdCo₅ was once examined as a permanent magnet material (though now overshadowed by rare-earth magnets based on neodymium or samarium).

Summarized, gadolinium’s chemistry is dominated by the Gd³⁺ ion. It forms stable ionic oxides, halides, sulfides, etc., typically with high ionic character. The compounds of Gd(III) are often fluorescent under UV light and have notable optical properties; for instance, Gd₂O₂S doped with europium is a red phosphor used in display screens.

Physical Properties

Gadolinium metal is a lustrous, silvery-gray material (often described as slightly yellowish-white). It’s somewhat soft (malleable and ductile) and takes a bright polish like other rare-earth metals. The room-temperature density of gadolinium is about 7.90 grams per cubic centimeter. It has a high melting temperature of 1585 K (1312 °C) and a boiling point near 3546 K (3273 °C). The thermal expansion coefficient is moderate and its specific heat at room temperature is around 25 J·mol⁻¹·K⁻¹.

In terms of magnetism, gadolinium stands out. Below its Curie point (~293 K), gadolinium metal is ferromagnetic, meaning its atomic moments align even without an external field. Above that (for example at 300 K or body temperature ~310 K), it becomes strongly paramagnetic – it does not retain magnetization but responds very strongly to applied magnetic fields. In fact, at human body temperature gadolinium has one of the largest paramagnetic susceptibilities of all elements, due to its 7 unpaired 4f electrons in Gd³⁺. This is why gadolinium compounds are excellent for MRI contrast.

Electrically, gadolinium is a good conductor of electricity, typical of metals. Its electrical resistivity at 20 °C is about 1.3×10⁻⁶ Ω·m. Its thermal conductivity at room temperature is on the order of 10.6 W·m⁻¹·K⁻¹, which is lower than many transition metals but similar to other lanthanides. Gadolinium’s surface in air is protected by a thin oxide film, which can flake off (“spall”) to expose fresh metal. If heated strongly in oxygen, gadolinium will burn vigorously, forming Gd₂O₃. It reacts with steam or hot water to release hydrogen gas.

Optically, gadolinium metal reflects visible light with a silver sheen. Its spectrum (viewed as an atom) shows many lines in the ultraviolet and visible regions, but these are of interest mostly in research settings. Gadolinium doped into crystals (as Gd³⁺ ions) exhibits sharp emission lines in the UV and sometimes visible, due to f–f electronic transitions, which find use in laser and phosphor materials. For example, Gd³⁺ emission around 313 nm and 316 nm is used in some ultraviolet lamps.

Overall, the physical properties of gadolinium – high density, high melting point, strong magnetism, reasonable thermal and electrical conductivity – reflect a typical heavy metallic element with 4f electrons. These properties, especially the magnetic ones, are key to many applications.

Chemical Reactivity and Trends

Gadolinium metal is quite reactive chemically, as expected for an electropositive rare-earth metal. In dry air it tarnishes slowly, forming a dull oxide layer; in moist air it can corrode more quickly. When heated, it burns in oxygen to form gadolinium(III) oxide (Gd₂O₃). Gadolinium reacts with water to yield hydrogen gas and gadolinium hydroxide: \[\text{2 Gd + 6 H₂O → 2 Gd(OH)₃ + 3 H₂}\] Though this reaction proceeds slowly at room temperature, it accelerates with heat or steam, like many lanthanides.

With acids, gadolinium dissolves readily. For example, dilute hydrochloric acid or sulfuric acid will convert Gd metal into GdCl₃ or Gd₂(SO₄)₃, liberating hydrogen. These Gd(III) salts are typically soluble in water. In water, Gd³⁺ is a strong Lewis acid and the solutions are slightly acidic due to formation of Gd(OH)²⁺ and Gd(OH)₃ complexes; strong bases precipitate the insoluble hydroxide Gd(OH)₃. In a sense, gadolinium(III) is “hydrolysis prone,” meaning it acts as a powerful acidic cation in water.

As is true across the lanthanide series, the +3 oxidation state is by far the most stable. The +2 oxidation state can exist in some crystalline halides like GdCl₂, but such +2 compounds are rare for gadolinium and typically require special conditions. A formal +4 state (e.g. in GdO₂) has been reported in trace amounts under extreme conditions or in complex lattices, but it is not stable in normal chemistry. Therefore, chemical reactions involving gadolinium usually involve Gd(III) transforming into other Gd(III) compounds or Gd metal.

In terms of periodic trends, gadolinium fits the pattern of the middle lanthanoids. Its “lanthanide contraction” means its ionic radius is somewhat smaller than lighter lanthanoids (like neodymium). For coordination chemistry, the Gd³⁺ ionic radius (eight-coordinate) is about 119 pm. Because of the contraction, Gd behaves chemically similarly to neighboring elements like Tb or Eu, though Eu²⁺ chemistry diverges because Eu²⁺ is stable. Gd does not exhibit stable Eu-like +2 chemistry and is thus less reactive with reducing agents. Compared to the lighter 3d transition metals, Gd is much more electropositive: it forms ionic compounds rather than covalent complexes for the most part.

When exposed to common reagents, Gd metal also reacts with halogens (fluorine, chlorine, bromine, iodine) to form the corresponding GdX₃ (for example, GdCl₃ is formed by burning Gd in Cl₂ gas or by reacting Gd₂O₃ with HCl). It reacts with sulfur and nitrogen at elevated temperatures to give sulfides (Gd₂S₃) and nitrides (GdN). Essentially, gadolinium metal behaves like a strong reductant that is oxidized to Gd³⁺ by most nonmetals.

In corrosive environments (like acids), gadolinium metal dissolves, but the oxide film can afford some passivation in moist air (until it peels off). Standard electrode potentials place Gd lower (more negative) than hydrogen, indicating it will displace H₂ from acids. In the common reactivity series of metals, gadolinium would lie among the active metals (further to the left than Zn, above the lanthanides), similar to other rare-earth metals.

Summarizing reactivity: gadolinium is a fairly reactive metal that oxidizes easily and does not form volatile compounds. Its chemistry is dominated by transitions between Gd(0) and Gd(III). Gd(III) salts in solution are usually colorless (due to the half-filled 4f shell, Gd³⁺ complexes are often nearly colorless) and precipitate as hydroxides or carbonates on adding base or CO₂. Complexation with chelators (like EDTA, DTPA) is strong, reflecting the high charge and large size of Gd³⁺.

Occurrence and Production

Gadolinium is not found free in nature but is relatively abundant among the rare-earth elements. Its crustal abundance is about 6.2 milligrams per kilogram (ppm) of Earth’s crust, making it more common than many metals like lead or tin. It typically occurs in minerals with other rare earths. Notable gadolinium-bearing minerals include bastnäsite Ce,La,Nd,Th)(CO₃)F], monazite Ce,La,Nd,Th)PO₄], and xenotime Y,REE)PO₄]. Because lanthanides have very similar chemistry, no mineral is exclusively Gd; it is dispersed among lanthanoid mixtures. Gadolinite (after which Gd is named) and euxenite are rare Gad-containing ores as well.

The largest reserves of rare earth minerals (containing Gd) are in China (Inner Mongolia’s Bayan Obo mine and others), which dominates global production. Other significant sources are in the United States (the Mountain Pass mine, mostly Ce/La but also containing Gd), Australia, India, Brazil, and countries of Africa. According to data, world production of gadolinium element (pure Gd) is on the order of a few hundred tonnes per year (for example, around 400 tonnes annually). China is by far the largest producer of pure Gd (often by processing mixed rare-earth concentrates), with the U.S., India, and Russia producing smaller amounts.

Extraction of gadolinium typically follows the common route for lanthanoids: mining of rare-earth ores, separation of the lanthanide mixture (often by solvent extraction or ion-exchange chromatography), and finally isolation of individual elements. For example, a mixture of rare-earth chlorides can be fractionally crystallized or extracted to yield a chloride enriched in Gd. The metal is then produced from GdCl₃ (or Gd₂O₃) by reduction. A common method is metallothermic reduction: heating GdCl₃ with calcium or aluminum powder to displace metal; or by the some other processes. Electrolysis of molten GdCl₃ can also yield gadolinium metal, though handling molten fluoride or chloride salts is required. In practice, adding calcium metal to molten GdCl₃ (in a sealed container) is an efficient way to get impure Gd, which can be purified by distillation or sublimation of GdCl₃.

Industrial production often keeps gadolinium as an alloy or mixture; neodymium-iron-boron magnets, for instance, usually come from an alloy called “mischmetal” which contains small percentages of Gd. Pure Gd metal is relatively rare and produced only when needed for specific applications (like contrast agents or specialty alloys).

In summary, gadolinium is mined as part of rare-earth minerals and separated by established lanthanide processing methods. Despite being “rare earth,” it is moderately plentiful and economically extracted wherever the overall rare-earth complex is available.

Applications and Technology

Gadolinium has a range of important uses, many exploiting its unique magnetic and nuclear properties. The most famous application is as the basis for MRI contrast agents in medicine. Gadolinium(III) chelates (for example, gadopentetate dimeglumine or gadobutrol) are injected intravenously to enhance contrast in magnetic resonance imaging. The paramagnetic Gd³⁺ ions shorten the relaxation time of nearby water protons, making tissues with Gd appear brighter on MRI scans. Almost all MRI contrast drugs use Gd ions tightly bound by organic ligands (such as DTPA or DOTA) to minimize free Gd³⁺ toxicity. These agents are widely used in diagnostic imaging of the brain, spine, and other organs.

In nuclear technology, gadolinium’s giant neutron capture cross-section is harnessed in several ways. Gadolinium can be used in control rods or burnable poison rods in nuclear reactors to regulate or dampen the neutron flux. It is especially useful in applications requiring efficient removal of thermal neutrons. Gd₂O₃ or Gd-containing glass can line reactor storage pools or radiation shielding blocks. Research experiments (such as neutrino detectors) add gadolinium to water or scintillator to tag neutrons more effectively. In neutron capture therapy for cancer treatment, gadolinium compounds introduced to tumors have been explored as agents that capture injected neutrons to produce localized radiation.

In magnetic applications, gadolinium and its alloys are notable for their high magnetic moments. Pure Gd metal was used in the past for low-temperature magnetic refrigerants via the magnetocaloric effect (the phenomenon where a magnetic material heats up or cools down upon magnetization/demagnetization). Gd exhibits a large magnetocaloric effect near room temperature, so gadolinium-based alloy compounds (like Gd₅(SixGe{1–x})₄) have been studied for energy-efficient refrigeration systems. However, commercial magnetic refrigerators typically use more complex rare-earth alloys. Gadolinium is also used to improve magnetic and mechanical properties of other alloys: small additions of Gd to steel or alloys can improve high-temperature performance (e.g. in turbines). Gd is sometimes alloyed with neodymium (NdFeB) magnets to raise their Curie temperature or increase coercivity. Pure Gd-containing permanent magnets are less common, because Nd and Sm are more powerful, but Gd adds fine-tuning capabilities.

In optoelectronic and luminescent applications, Gd plays a role as a dopant or host material. Gadolinium oxide and sulfide are bases for phosphors: e.g. Gd₂O₂S:Eu glows red under UV/x-ray excitation (used in color TV tubes and X-ray intensifying screens). Gd₂O₂S:Tb, Sm, Ce similarly produce green or blue emissions for flat-panel displays. Gd incorporates in garnet host crystals (like YAG) for certain solid-state lasers or scintillation counters. Gadolinium-containing scintillators (such as GSO – Gd₂SiO₅:Ce) are prized as radiation detectors for gamma rays and X-rays because Gd has high atomic number (Z=64) and good stopping power. Gd complexes are also used in luminescence thermometers and sensors (owing to sharp 4f–4f spectral lines).

Other technological uses include:

• Electronics and optics: Gd₂O₃ thin films are investigated as high-κ dielectrics in semiconductor devices. Gd is used in some ferrite cores and microwave devices due to its high permeability. Gd5Ge2Si_2 compounds have been explored in magnetocaloric cooling.
• Medical sources: ^153Gd (radioactive) is used as a calibration source in dual-energy X-ray absorptiometry (DXA) machines for bone density scanning. Its gamma emissions at 100–250 keV make it suitable for calibration.
• Magnetic Refrigeration prototypes: Experimental low-power fridges have been built using blocks of gadolinium or Gd-based alloys, illustrating the concept of magnetic cooling.
• High-energy physics: Gadolinium-loaded liquid scintillators or water are used in neutrino detectors (e.g. at Daya Bay or Super-Kamiokande) to tag neutron captures via Gd’s gamma showers.
• Catalysis: Though not a major catalyst, Gd compounds show activity in some polymerization and organic transformations – mostly of academic interest.

In everyday technology, Gd is not as ubiquitous as silicon or iron, but where specialized magnetic, nuclear, or luminescent properties are needed, gadolinium is valuable. Its role in MRI has been transformative in medicine. It also contributes to research in low-temperature physics, neutron science, and new refrigeration methods.

Biology, Environment, and Safety

Gadolinium has no known biological role in living organisms – it is not an essential mineral nutrient. As a heavy metal, gadolinium ions are toxic if they become biologically available. The free Gd³⁺ ion interferes with calcium ion channels in cells and can disrupt metabolic processes. For this reason, gadolinium in medical contrast agents is always tightly chelated; the chelating molecules keep Gd³⁺ bound and facilitate rapid excretion. In healthy patients, over 98% of an injected gadolinium chelate is eliminated by the kidneys within a day.

However, concerns have arisen about Gd retention and toxicity. In patients with impaired kidney function, gadolinium-based contrast can lead to a rare but serious condition called nephrogenic systemic fibrosis (NSF), involving fibrosis of skin and organs. Regulatory agencies worldwide now restrict gadolinium contrast in such patients. There is also evidence that trace Gd from contrast agents deposits in brain tissue after repeated use, though the clinical significance of this is still under study.

Environmentally, gadolinium is introducing itself as an emerging contaminant. Because contrast agents are excreted unchanged, gadolinium salts (chelated) enter wastewater and eventually surface water. Studies have found anthropogenic gadolinium in rivers and drinking water near urban areas. While current concentrations are low, the ecological impact is uncertain. Gd(III) is highly insoluble as a free ion (pKₐ of Gd(OH)₃ ≈ 8.9), but in the environment Gd remains bound to the original chelators or can replace other rare earths in sediments.

Exposure to gadolinium compounds (oxide, salts) in the workplace is managed by typical metal-handling precautions. Inhalation of gadolinium oxide dust or chloride fumes can irritate the lungs; ingestion can cause gastrointestinal discomfort. Gadolinium itself is moderately reactive, so fine metal powder is combustible in air. Personal protective equipment (gloves, eye protection) is advised when handling Gd metal or compounds. There are no specific occupational exposure limits unique to gadolinium in many jurisdictions, but it would be treated similarly to other toxic heavy metals.

Standard safety data: Gadolinium metal is electrically conductive, so avoid electrocution hazards when machining. Gd(III) salts are generally not extremely toxic by ingestion (LD₅₀ for some gadolinium salts in animals is on the order of ~1000 mg/kg), but inhalation or intravenous exposure is more dangerous. The chelates used in hospitals are generally resistant to releasing Gd³⁺, making them safe enough for medical use under guidelines.

In summary, gadolinium’s environmental and biological impact stems mainly from human use. It is not a nutrient for organisms, and in free form it is toxic. Handling requires care, especially for the dust and solvated ions. Disposal of gadolinium waste (e.g. spent contrast agent, metal scrap) is done according to heavy metal waste regulations, often through specialist recycling companies that recover the rare earth.

History and Etymology

Gadolinium was first identified in 1880 by Swiss chemist Jean Charles Galissard de Marignac. He analyzed gadolinite, a mineral discovered in Ytterby, Sweden (also famous for other rare-earth elements), and recognized by its spectra the presence of a new element oxide. The mineral gadolinite itself had been known to contain a “new earth” metal since 1794, when Finnish chemist Johan Gadolin discovered an unknown oxide in a mineral sample. The new element was named gadolinium (Latinized from Gadolin’s name) in honor of Johan Gadolin. The mineral was originally called “ytterbite,” but Gadolin referred to it as “gadolinite” in his 1800 paper, giving rise to the name of the element decades later.

Pure gadolinium metal was not isolated until about 1886, when the French chemist Paul-Émile Lecoq de Boisbaudran electrolyzed gadolinium chloride (or reduced it chemically) to obtain the element. In those early years, separation of gadolinium from other rare-earth elements was difficult because they were often mixed together. As isolation techniques improved (first by fractional crystallization and later by solvent extraction in the mid-20th century), pure gadolinium samples became available for study.

The name “gadolinium” thus honors Gadolin but also indirectly references the Swedish village of Ytterby, which contributed other element names (ytterbium, yttrium, terbium, erbium). Ytterby’s quarry, where gadolinite was found, has a unique legacy of element discovery.

Important milestones in Gd history include: its spectroscopic discovery in 1880, isolation of the metal around 1886, and recognition of its magnetic and nuclear properties in the 20th century. In 1938, gadolinium was used in early particle physics experiments for neutron detection. The development of MRI in the 1970s and 1980s led to gadolinium-based contrast agents, first approved by the FDA in 1988 (gadopentetate dimeglumine). The remarkable neutron-absorption of Gd-157 has been known since mid-20th century and was applied in reactor design.

Etymologically, “gadolinium” follows the convention of lanthanoid names ending in “-ium.” The atomic symbol Gd was assigned as a straightforward abbreviation. No alchemical or mythological roots are involved; it is purely a patronym honoring an early chemist.

Thus, from its 19th-century discovery in a Swedish mineral to its 20th-century role in medical imaging and nuclear science, gadolinium’s history reflects the broader story of rare-earth chemistry: challenging separation, unique physical phenomena, and modern technological uses.

Data Table

Property / Identifier	Value / Description
Name	Gadolinium
Symbol	Gd
Atomic number (Z)	64
Atomic mass	157.25 (standard atomic weight)
Electron configuration	[Xe] 4f⁷ 5d¹ 6s²
Oxidation states	+3 (primary), +2, +4 (rare)
Period, block	Period 6, block f (lanthanoid series)
Crystal structure (RT)	Hexagonal close-packed (α-phase)
Magnetic ordering	Ferromagnetic below 293 K (Curie point); paramagnetic above
Density (20 °C)	7.90 g·cm⁻³ (solid)
Melting point	1585 K (1312 °C)
Boiling point	3546 K (3273 °C)
Electrical resistivity (20 °C)	~1.31×10⁻⁶ Ω·m
Thermal conductivity (300 K)	~10.6 W·m⁻¹·K⁻¹
Electronegativity (Pauling)	1.20
First ionization energy	6.15 eV (≈594 kJ·mol⁻¹)
Atomic radius (empirical)	~180 pm
Gd³⁺ ionic radius (VIII coord.)	~119 pm
Stable isotopes	^154Gd, ^155Gd, ^156Gd, ^157Gd, ^158Gd, ^160Gd
Notable radionuclides	^152Gd (t₁/₂ ~1.1×10^14 y), ^153Gd (241 d), ^148Gd (86.9 y), ^150Gd (1.8×10^6 y)
Thermal neutron cross-section (^157Gd)	~2.6×10^5 barns
Occurrence in crust	~6.2 mg·kg⁻¹ (≈6.2 ppm)
Major commercial uses	MRI contrast agents, neutron absorbers phosphors, alloys (steel, magnets), research optics
Discovery	Identified 1880 (by J.C. de Marignac)
Named after	Johan Gadolin (Finnish chemist)