Editing Actinide (section)

=== Physical properties ===
{|class="wikitable" style ="text-align: center"
|-
| [[File:ActinidesLattice.png|400px]]
| [[File:ACTIION.PNG|400px]]
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|Major crystal structures of some actinides vs. temperature
|[[Metallic bond|Metallic]] and [[ionic radius|ionic]] radii of actinides<ref name="g1263" />
|}

[[File:Radioisotope thermoelectric generator plutonium pellet.jpg|thumb|A pellet of <sup>238</sup>PuO<sub>2</sub> to be used in a [[radioisotope thermoelectric generator]] for either the [[cassini spacecraft|Cassini]] or [[galileo spacecraft|Galileo]] mission. The pellet produces 62 watts of heat and glows because of the heat generated by the radioactive decay (primarily α). Photo is taken after insulating the pellet under a [[graphite]] blanket for minutes and removing the blanket.]]
[[File:Californium.jpg|thumb|left|[[Californium]]]]

Actinides are typical metals. All of them are soft and have a silvery color (but tarnish in air),<ref name=g1264>Greenwood, p. 1264</ref> relatively high [[density]] and plasticity. Some of them can be cut with a knife. Their [[electrical resistivity]] varies between 15 and 150 μΩ·cm.<ref name="g1263" /> The hardness of thorium is similar to that of soft steel, so heated pure thorium can be rolled in sheets and pulled into wire. Thorium is nearly half as dense as uranium and plutonium, but is harder than either of them. All actinides are radioactive, [[paramagnetism|paramagnetic]], and, with the exception of actinium, have several crystalline phases: plutonium has seven, and uranium, neptunium and californium three. The [[crystal structure]]s of protactinium, uranium, neptunium and plutonium do not have clear analogs among the lanthanides and are more similar to those of the 3''d''-[[transition metal]]s.<ref name="Yu. D. Tretyakov" />

All actinides are [[Pyrophoricity|pyrophoric]], especially when finely divided, that is, they spontaneously ignite upon reaction with air at room temperature.<ref name=g1264 /><ref>{{cite book|quote=Many actinide metals, hydrides, carbides, alloys and other compounds may ignite at room temperature in a finely divided state.|url=https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Modules_and_Websites_(Inorganic_Chemistry)/Descriptive_Chemistry/Elements_Organized_by_Block/4_f-Block_Elements/The_Actinides/1General_Properties_and_Reactions_of_The_Actinides|title= General Properties and Reactions of the Actinides|date=22 May 2015 |publisher= LibreTexts}}</ref> The [[melting point]] of actinides does not have a clear dependence on the number of ''f''-electrons. The unusually low melting point of neptunium and plutonium (~640&nbsp;°C) is explained by [[Hybridization (chemistry)|hybridization]] of 5''f'' and 6''d'' orbitals and the formation of directional bonds in these metals.<ref name="Yu. D. Tretyakov" />

{| class="wikitable collapsible collapsed"  style="margin-left: 1em; width:75%;"
|+ Comparison of [[ionic radius|ionic radii]] of lanthanides and actinides<ref>Myasoedov, pp. 30–31</ref>
|-
! [[Lanthanide]]s
! Ln<sup>3+</sup>, Å
! Actinides
! An<sup>3+</sup>, Å
! An<sup>4+</sup>, Å
|-
| [[Lanthanum]]|| 1.061|| [[Actinium]]|| 1.11||–
|-
| [[Cerium]]|| 1.034|| [[Thorium]]|| 1.08|| 0.99
|-
| [[Praseodymium]]|| 1.013|| [[Protactinium]]|| 1.05|| 0.93
|-
| [[Neodymium]]|| 0.995|| [[Uranium]]|| 1.03|| 0.93
|-
| [[Promethium]]|| 0.979|| [[Neptunium]]|| 1.01|| 0.92
|-
| [[Samarium]]|| 0.964|| [[Plutonium]]|| 1.00|| 0.90
|-
| [[Europium]]|| 0.950|| [[Americium]]|| 0.99|| 0.89
|-
| [[Gadolinium]]|| 0.938|| [[Curium]]|| 0.98|| 0.88
|-
| [[Terbium]]|| 0.923|| [[Berkelium]] ||–||–
|-
| [[Dysprosium]]|| 0.908|| [[Californium]] ||–||–
|-
| [[Holmium]]|| 0.894|| [[Einsteinium]] ||–||–
|-
| [[Erbium]]|| 0.881|| [[Fermium]] ||–||–
|-
| [[Thulium]]|| 0.869|| [[Mendelevium]] ||–||–
|-
| [[Ytterbium]]|| 0.858|| [[Nobelium]] ||–||–
|-
| [[Lutetium]]|| 0.848|| [[Lawrencium]] ||–||–
|}