Why is +3 the dominant oxidation state for gadolinium?

Gadolinium has the ground-state configuration [Xe] 4f⁷ 5d¹ 6s². Losing the 5d¹ and both 6s² electrons (3 electrons total) gives Gd³⁺ with configuration [Xe] 4f⁷ — exactly half-filled. Each of the seven 4f orbitals holds one electron, maximizing exchange energy. This half-filled 4f⁷ arrangement is exceptionally stable, which is why Gd³⁺ dominates and Gd⁴⁺ (which would disrupt the half-fill) is not observed under normal conditions.

Why is Gd³⁺ used in MRI contrast agents?

Gd³⁺ has 7 unpaired f-electrons, making it strongly paramagnetic. This large magnetic moment shortens the T1 relaxation time of nearby water protons, brightening signal on T1-weighted MRI images. Free Gd³⁺ is toxic, so it is chelated with ligands like DTPA (Magnevist) or DOTA (used in gadoterate, sold as Dotarem) that cage the ion and prevent it from releasing in the body.

What is Gd²⁺ and why is it so rare?

Gd²⁺ would have the configuration [Xe] 4f⁷ 5d¹ — retaining one d electron after losing only two electrons. This is less stable than the clean half-filled 4f⁷ of Gd³⁺, so there is no thermodynamic driving force to stop at +2. Gd²⁺ exists only in a few solid-state divalent lanthanide compounds under reducing conditions.

Free Gd³⁺ ions are toxic. They can block calcium channels and deposit in tissues. In patients with impaired kidney function, deposition of gadolinium can lead to nephrogenic systemic fibrosis (NSF), a serious fibrotic disease. MRI contrast agents use stable chelates to minimize free Gd³⁺ release; macrocyclic chelates like Gd-DOTA are more stable than linear ones like Gd-DTPA.

How does gadolinium relate to neutron absorption?

Natural gadolinium has a thermal-neutron absorption cross-section of about 49,700 barns. Its ¹⁵⁵Gd and ¹⁵⁷Gd isotopes are especially strong absorbers, at about 61,100 and 259,000 barns respectively. This makes gadolinium useful as a neutron poison in nuclear reactor control and as a burnable absorber in fuel rods. It is also the basis of gadolinium-based neutron capture therapy (Gd-NCT) research.

What are the phosphor applications of gadolinium?

Gd³⁺ is used as a host lattice or co-activator in phosphor materials. Gd₂O₂S:Tb (gadolinium oxysulfide doped with terbium) is a bright green phosphor used in X-ray imaging intensifying screens and CT detector scintillators. GdAlO₃ and other gadolinium compounds serve as phosphor hosts for various rare-earth dopants.

Gadolinium Oxidation States Reference

Reference for gadolinium oxidation states: the dominant +3 state (stable 4f⁷ half-filled shell), rare +2, theoretical +4, key compounds, and MRI contrast agent applications.

Atomic # 64 Gd Gadolinium

Atomic Mass

157.25 u

Group

Lanthanide

Period

Block

f-block

Electronegativity

1.20 (Pauling)

Oxidation States

+3 (dominant)

Gadolinium is an f-block lanthanide with ground-state configuration [Xe] 4f⁷ 5d¹ 6s². Losing the 5d¹ and 6s² electrons produces Gd³⁺ ([Xe] 4f⁷) — a perfectly half-filled f subshell with one electron in each of the seven f orbitals. This arrangement maximizes exchange energy and is exceptionally stable, making +3 the overwhelmingly dominant state. The +2 state is very rare; +4 would disrupt the half-filled 4f⁷ and is not observed in normal chemistry.

State	Name	f-electrons	Config (after Xe)	Stability	Notes
0	Elemental	7 (+ 5d¹ 6s²)	[Xe] 4f⁷ 5d¹ 6s²	Elemental metal	Silvery-white metal; ferromagnetic below 20 °C (Curie point)
+2	Gadolinium(II)	7 (+ 5d¹)	[Xe] 4f⁷ 5d¹	Very rare / unstable	Only in a few solid-state compounds under reducing conditions
+3	Gadolinium(III)	7	[Xe] 4f⁷	Dominant / very stable	Half-filled 4f⁷; 7 unpaired electrons; strongly paramagnetic; basis of MRI contrast
+4	Gadolinium(IV)	6	[Xe] 4f⁶	Theoretical only	Not observed in practice; would disrupt stable 4f⁷ half-fill

Half-filled 4f⁷ stability
Both Gd²⁺ and Gd³⁺ have a 4f⁷ configuration, but Gd³⁺ is far more stable. In Gd²⁺ the 5d¹ electron remains, creating an asymmetric configuration. Losing that extra electron to reach Gd³⁺ yields a clean [Xe] 4f⁷ — every f orbital singly occupied — with maximum exchange energy.

Lanthanide contraction
Across the lanthanide series, poor 4f shielding causes the nuclear charge to pull the outer electrons inward with each added proton. By gadolinium (Z = 64), the ionic radius of Gd³⁺ is 93.8 pm — smaller than La³⁺ (103.2 pm) despite being 13 elements heavier.

Nearly all gadolinium compounds contain Gd³⁺. The most important industrial and medical compounds are listed below, including the MRI contrast chelates that make gadolinium one of the most clinically significant f-block elements.

Compound	Formula	Gd State	Appearance	Notes
Gadolinium(III) Oxide	Gd₂O₃	+3	White powder	Most common Gd oxide; used in phosphors (X-ray screens), neutron absorbers, and as a starting material for other Gd compounds.
Gadolinium(III) Chloride	GdCl₃	+3	Colorless crystals	Soluble in water; common laboratory reagent; used to synthesize organogadolinium and coordination compounds.
Gadolinium(III) Nitrate	Gd(NO₃)₃	+3	Colorless crystals	Highly soluble; used in solution-phase synthesis of gadolinium-containing materials and as a precursor.
Gadolinium(III) Fluoride	GdF₃	+3	White solid	Very low solubility; used in optical fibers and as a neutron absorber coating.
Gadolinium Oxysulfide	Gd₂O₂S	+3	White powder	Host lattice for Tb³⁺ phosphor (Gd₂O₂S:Tb); intense green emitter; used in X-ray intensifying screens and CT scintillators.
Gadolinium Gallium Garnet	Gd₃Ga₅O₁₂	+3	Colorless crystal (GGG)	Optical substrate and laser host; used as a substrate for magnetic bubble memory and magneto-optical devices.
Gadopentetate (Gd-DTPA)	Gd-DTPA²⁻	+3	Clear aqueous solution	Linear chelate; brand name Magnevist; first approved MRI contrast agent (1988); higher risk of Gd retention vs. macrocyclic chelates.
Gadoterate (Gd-DOTA)	[Gd(DOTA)]⁻	+3	Clear aqueous solution	Macrocyclic chelate; brand name Dotarem; very high thermodynamic and kinetic stability; lower risk of free Gd³⁺ release in vivo.

MRI contrast: why chelation matters
Free Gd³⁺ mimics Ca²⁺ in vivo and is acutely toxic. Chelation with DTPA or DOTA encages the ion in a stable complex that is renally excreted before significant Gd³⁺ release occurs. Macrocyclic ligands (DOTA-family) form kinetically inert cages; linear ligands (DTPA-family) are thermodynamically stable but kinetically labile and more prone to transmetallation with endogenous Zn²⁺ or Ca²⁺.

Gd (neutral)

4f orbitals

↑ ↓

7 f-electrons (all unpaired) + 1 d-electron + 2 s-electrons

Full config: [Xe] 4f⁷ 5d¹ 6s²

One electron occupies 5d before completing 4f — same anomaly as La, Ce, Gd, Lu. The half-filled 4f⁷ gains extra stability if 5d¹ is also occupied rather than forcing the 8th electron into 4f.

Gd³⁺

4f orbitals

↑ ↓

7 f-electrons (all unpaired)

Full config: [Xe] 4f⁷

Loses 5d¹ and 6s² first (highest-energy electrons). Result: clean half-filled 4f⁷. All 7 f-electrons unpaired → strongly paramagnetic (7 unpaired e⁻, μ_eff ≈ 7.94 BM).

Why Gd has a 5d¹ in the neutral atom
Most lanthanides fill 4f straight across (e.g., La: [Xe] 5d¹ 6s², then Ce–Yb: [Xe] 4fⁿ 6s²). Gadolinium is an exception: [Xe] 4f⁷ 5d¹ 6s² rather than [Xe] 4f⁸ 6s². Placing 8 electrons into 4f would pair one orbital and cost more exchange energy than the gain from keeping 4f⁷ half-filled and placing the extra electron in 5d. The net energy favors the half-filled 4f⁷ arrangement.

Ionization	Energy (kJ/mol)	Electron removed from
IE₁ → Gd⁺	593.4	6s (highest-energy electron in neutral Gd)
IE₂ → Gd²⁺	1170	6s (removes second 6s electron)
IE₃ → Gd³⁺	1990	5d¹ (now 6s empty; removes the 5d¹ electron)
IE₄ → Gd⁴⁺	4250	4f (large jump — disrupts stable 4f⁷ half-fill)

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Summary

Gadolinium (Gd) is a lanthanide at atomic number 64 with ground-state electron configuration [Xe] 4f⁷ 5d¹ 6s². Its overwhelming dominant oxidation state is +3, achieved by losing the 5d¹ and 6s² electrons to leave a stable half-filled 4f⁷ configuration — one electron in each of the seven f orbitals. The resulting Gd³⁺ ion is paramagnetic with 7 unpaired electrons, making it highly useful as an MRI contrast agent. Gd²⁺ is very rare and unstable; Gd⁴⁺ is only theoretical. Key compounds include Gd₂O₃ (gadolinium(III) oxide), GdCl₃ (gadolinium(III) chloride), and chelated forms such as Gd-DTPA (Magnevist) and Gd-DOTA (gadoterate, sold as Dotarem) used in clinical MRI.

How it works

Click a tab — Oxidation States, Compounds, Electron Config, or Physical Props — to explore each section.
The Oxidation States panel lists all known states with stability, f-electron count, and key notes.
The Compounds panel shows common gadolinium compounds including MRI contrast agents.
The Electron Config panel shows orbital diagrams for Gd and Gd³⁺ side by side.
The Physical Props panel provides atomic and material data for quick reference.
Click any monospace table cell to copy its value to the clipboard.

Use cases

Students learning f-block (lanthanide) chemistry and the stability of half-filled 4f subshells.
Chemistry teachers explaining why lanthanides almost exclusively adopt the +3 state.
Medical physicists or radiologists understanding the paramagnetic basis of gadolinium MRI contrast agents.
Toxicology students researching nephrogenic systemic fibrosis and why Gd³⁺ chelation matters.
Anyone revising for exams covering f-block chemistry, coordination compounds, or inorganic chemistry.

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Last updated: 2026-06-19 · Reviewed by Nham Vu

Gadolinium Oxidation States Reference

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