Editing Gadolinium (section)

==Characteristics==
[[File:Gadolinium-2.jpg|thumb|left|150px|A sample of gadolinium metal]]

===Physical properties===
Gadolinium is the eighth member of the [[lanthanide]] series. In the [[periodic table]], it appears between the elements [[europium]] to its left and [[terbium]] to its right, and above the [[actinide]] [[curium]]. It is a silvery-white, [[malleability|malleable]], [[ductility|ductile]] [[rare-earth element]]. Its 64 electrons are arranged in the configuration of [Xe]4f<sup>7</sup>5d<sup>1</sup>6s<sup>2</sup>, of which the ten 4f, 5d, and 6s electrons are [[valence electron|valence]].

Like most other metals in the lanthanide series, three electrons are usually available as valence electrons. The remaining 4f electrons are too strongly bound: this is because the 4f orbitals penetrate the most through the inert xenon core of electrons to the nucleus, followed by 5d and 6s, and this increases with higher ionic charge. Gadolinium crystallizes in the [[hexagonal crystal system|hexagonal close-packed]] α-form at room temperature.   At temperatures above {{convert|1235|C}}, it forms or transforms into its β-form, which has a [[body-centered cubic]] structure.<ref name="Greenwood" />

The [[isotope]] gadolinium-157 has the highest [[thermal neutron|thermal-neutron]] [[neutron capture|capture]] cross-section among any stable nuclide: about 259,000 [[barn (unit)|barns]]. Only [[xenon-135]] has a higher capture cross-section, about 2.0&nbsp;million barns, but this isotope is [[radioactive]].<ref name="barn">{{cite journal |url= https://www.ncnr.nist.gov/resources/n-lengths/elements/gd.html |title= Gadolinium |access-date= 6 June 2009 |journal= Neutron News |volume= 3 |issue= 3 |date= 1992 |page= 29}}</ref>

Gadolinium is believed to be [[ferromagnetism|ferromagnetic]] at temperatures below {{convert|20|C}}<ref name="CRC2" /> and is strongly [[paramagnetism|paramagnetic]] above this temperature. In fact, at body temperature, gadolinium exhibits the greatest paramagnetic effect of any element.<ref name="Wininger">{{cite journal |last1=Wininger |first1=Kevin |title=Contrast Media's Molecular Architecture |journal=Radiologic Technology |date=January–February 2022 |volume=93 |issue=3 |page=341 |pmid=35017275 |url=https://cdn.mycrowdwisdom.com/asrt/CE%20Column/RADT22_JF_MolArch.pdf |access-date=27 November 2023}}</ref> There is evidence that gadolinium is a helical antiferromagnetic, rather than a ferromagnetic, below {{convert|20|C}}.<ref name="CoeySkumryev1999">{{cite journal |vauthors= Coey JM, Skumryev V, Gallagher K |journal=Nature |volume=401 |issue=6748 |year=1999 |pages=35–36|issn=0028-0836|doi=10.1038/43363 |title= Rare-earth metals: Is gadolinium really ferromagnetic?|bibcode=1999Natur.401...35C|s2cid=4383791 }}</ref> Gadolinium demonstrates a [[magnetic refrigeration#The magnetocaloric effect|magnetocaloric effect]] whereby its temperature increases when it enters a magnetic field and decreases when it leaves the magnetic field. A significant magnetocaloric effect is observed at higher temperatures, up to about 300&nbsp;[[kelvin]]s, in the compounds Gd<sub>5</sub>(Si<sub>1−''x''</sub>Ge<sub>''x''</sub>)<sub>4</sub>.<ref name="r27" />

Individual gadolinium atoms can be isolated by encapsulating them into [[fullerene]] molecules, where they can be visualized with a [[transmission electron microscope]].<ref>{{cite journal |doi= 10.1021/nl034621c |title= Evidence for the Intramolecular Motion of Gd Atoms in a Gd<sub>2</sub>@C<sub>92</sub> Nanopeapod |date= 2003 |author= Suenaga, Kazu |journal= Nano Letters |volume= 3 |pages= 1395 |first2= Risa |first3= Takashi |first4= Toshiya |first5= Hisanori |first6= Sumio |last2= Taniguchi |last3= Shimada |last4= Okazaki |last5= Shinohara |last6= Iijima|bibcode= 2003NanoL...3.1395S |issue= 10}}</ref> Individual Gd atoms and small Gd clusters can be incorporated into [[carbon nanotubes]].<ref>{{cite journal |vauthors= Hashimoto A, Yorimitsu H, Ajima K, Suenaga K, Isobe H, Miyawaki J, Yudasaka M, Iijima S, Nakamura E |title= Selective deposition of a gadolinium(III) cluster in a hole opening of single-wall carbon nanohorn |journal= Proceedings of the National Academy of Sciences, USA |volume= 101 |issue= 23 |pages= 8527–30 |date= June 2004 |pmid= 15163794 |pmc= 423227 |doi= 10.1073/pnas.0400596101 |bibcode= 2004PNAS..101.8527H|doi-access= free }}</ref>

===Chemical properties===
{{Category see also|Gadolinium compounds}}
Gadolinium combines with most elements to form Gd(III) derivatives. It also combines with nitrogen, carbon, sulfur, phosphorus, boron, selenium, silicon, and [[arsenic]] at elevated temperatures, forming binary compounds.<ref name="Wiberg">{{Holleman&Wiberg}}</ref>

Unlike the other rare-earth elements, metallic gadolinium is relatively stable in dry air. However, it [[tarnish]]es quickly in moist air, forming a loosely-adhering [[gadolinium(III) oxide]] ({{chem2|Gd2O3}}):
:{{chem2|4 Gd + 3 O2 → 2 Gd2O3}},
which [[spall#Corrosion|spalls]] off, exposing more surface to oxidation.

Gadolinium is a strong [[reducing agent]], which reduces oxides of several metals into their elements. Gadolinium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form [[gadolinium(III) hydroxide]] ({{chem2|Gd(OH)3}}):
:{{chem2|2 Gd + 6 H2O → 2 Gd(OH)3 + 3 H2}}.

Gadolinium metal is attacked readily by dilute [[sulfuric acid]] to form solutions containing the colorless Gd(III) ions, which exist as {{chem2|[Gd(H2O)9](3+)}} complexes:<ref>{{cite web |url= https://www.webelements.com/gadolinium/chemistry.html |title= Chemical reactions of Gadolinium |date= 1993–2018|author= Mark Winter|publisher= The University of Sheffield and WebElements |access-date=6 June 2009}}</ref>
:{{chem2|2 Gd + 3 H2SO4 + 18 H2O → 2 [Gd(H2O)9](3+) + 3 SO4(2-) + 3 H2}}.

====Chemical compounds====
In the great majority of its compounds, like many [[rare-earth metals]], gadolinium adopts the [[oxidation state]] +3. However, gadolinium can be found on rare occasions in the 0, +1 and +2 oxidation states. All four trihalides are known. All are white, except for the iodide, which is yellow. Most commonly encountered of the halides is [[gadolinium(III) chloride]] ({{chem2|GdCl3}}). The oxide dissolves in acids to give the salts, such as [[gadolinium(III) nitrate]].

Gadolinium(III), like most lanthanide ions, forms [[coordination complex|complexes]] with high [[coordination number]]s. This tendency is illustrated by the use of the chelating agent [[DOTA (chelator)|DOTA]], an octa[[denticity|dentate]] ligand. Salts of [Gd(DOTA)]<sup>−</sup> are useful in [[magnetic resonance imaging]]. A variety of related chelate complexes have been developed, including [[gadodiamide]].

Reduced gadolinium compounds are known, especially in the solid state. Gadolinium(II) halides are obtained by heating Gd(III) halides in presence of metallic Gd in [[tantalum]] containers. Gadolinium also forms the sesquichloride {{chem2|Gd2Cl3}}, which can be further reduced to GdCl by annealing at {{convert|800|C}}. This gadolinium(I) chloride forms platelets with layered graphite-like structure.<ref>{{cite book |page=1128 |url=https://books.google.com/books?id=U3MWRONWAmMC&pg=PA1128 |title= Advanced inorganic chemistry |edition= 6th |author= Cotton |publisher= Wiley-India |date= 2007 |isbn= 978-81-265-1338-3}}</ref>

===Isotopes===
{{Main|Isotopes of gadolinium}}
Naturally occurring gadolinium is composed of six stable isotopes, <sup>154</sup>Gd, <sup>155</sup>Gd, <sup>156</sup>Gd, <sup>157</sup>Gd, <sup>158</sup>Gd and <sup>160</sup>Gd, and one [[radioisotope]], <sup>152</sup>Gd, with the isotope <sup>158</sup>Gd being the most abundant (24.8% [[natural abundance]]). The predicted double beta decay of <sup>160</sup>Gd has never been observed (an experimental lower limit on its [[half-life]] of more than 1.3×10<sup>21</sup> years has been measured<ref name="DBD">{{Cite journal |last1=Danevich |first1=F. A. |last2=Kobychev |first2=V. V. |last3=Ponkratenko |first3=O. A. |last4=Tretyak |first4=V. I. |last5=Zdesenko |first5=Yu. G. |date=2001-11-05 |title=Quest for double beta decay of 160Gd and Ce isotopes |url=https://www.sciencedirect.com/science/article/pii/S0375947401009836 |journal=Nuclear Physics A |volume=694 |issue=1 |pages=375–391 |doi=10.1016/S0375-9474(01)00983-6 |issn=0375-9474|arxiv=nucl-ex/0011020 }}</ref>).

Thirty-three radioisotopes of gadolinium have been observed, with the most stable being <sup>152</sup>Gd (naturally occurring), with a half-life of about 1.08×10<sup>14</sup> years, and <sup>150</sup>Gd, with a half-life of 1.79×10<sup>6</sup> years. All of the remaining radioactive isotopes have half-lives of less than 75 years. The majority of these have half-lives of less than 25 seconds. Gadolinium isotopes have four metastable [[nuclear isomer|isomers]], with the most stable being <sup>143m</sup>Gd (''t''<sub>1/2</sub>= 110 seconds), <sup>145m</sup>Gd (''t''<sub>1/2</sub>= 85 seconds) and <sup>141m</sup>Gd (''t''<sub>1/2</sub>= 24.5 seconds).

The isotopes with [[atomic mass]]es lower than the most abundant stable isotope, <sup>158</sup>Gd, primarily decay by [[electron capture]] to isotopes of [[europium]]. At higher atomic masses, the primary [[decay mode]] is [[beta decay]], and the primary products are isotopes of [[terbium]].