Editing Lawrencium (section)

===Chemical===
[[File:F-block elution sequence.png|thumb|right|upright=1.4|Elution sequence of the late trivalent lanthanides and actinides, with ammonium α-HIB as eluant: the broken curve for lawrencium is a prediction.]]
In 1949, [[Glenn T. Seaborg]], who devised the [[actinide concept]], predicted that element 103 (lawrencium) should be the last actinide and that the {{chem2|Lr(3+)}} ion should be about as stable as {{chem2|Lu(3+)}} in [[aqueous solution]]. It was not until decades later that element 103 was finally conclusively synthesized and this prediction was experimentally confirmed.<ref name="Silva16447">{{harvnb|Silva|2011|pp=1644–7}}</ref>

Studies on the element, performed in 1969, showed that lawrencium reacts with [[chlorine]] to form a product that was most likely the trichloride, {{chem2|LrCl3}}. Its [[volatility (chemistry)|volatility]] was found to be similar to the chlorides of [[curium]], [[fermium]], and [[nobelium]] and much less than that of [[rutherfordium]] chloride. In 1970, chemical studies were performed on 1500&nbsp;atoms of <sup>256</sup>Lr, comparing it with divalent ([[nobelium|No]], [[barium|Ba]], [[radium|Ra]]), trivalent ([[fermium|Fm]], [[californium|Cf]], [[curium|Cm]], [[americium|Am]], [[actinium|Ac]]), and tetravalent ([[thorium|Th]], [[plutonium|Pu]]) elements. It was found that lawrencium [[extraction (chemistry)|coextracted]] with the trivalent ions, but the short half-life of <sup>256</sup>Lr precluded a confirmation that it [[elution|eluted]] ahead of {{chem2|[[mendelevium|Md]](3+)}} in the elution sequence.<ref name="Silva16447" /> Lawrencium occurs as the trivalent {{chem2|Lr(3+)}} ion in aqueous solution and hence its compounds should be similar to those of the other trivalent actinides: for example, lawrencium(III) [[fluoride]] ({{chem2|LrF3}}) and [[hydroxide]] ({{chem2|Lr(OH)3}}) should both be insoluble in water.<ref name="Silva16447" /> Due to the [[lanthanide contraction|actinide contraction]], the [[ionic radius]] of {{chem2|Lr(3+)}} should be smaller than that of {{chem2|Md(3+)}}, and it should elute ahead of {{chem2|Md(3+)}} when [[ammonium α-hydroxyisobutyrate]] (ammonium α-HIB) is used as an eluant.<ref name="Silva16447" /> Later 1987 experiments on the longer-lived isotope <sup>260</sup>Lr confirmed lawrencium's trivalency and that it eluted in roughly the same place as [[erbium]], and found that lawrencium's ionic radius was {{val|88.6|0.3|u=[[picometer|pm]]}}, larger than would be expected from simple extrapolation from [[periodic trend]]s.<ref name="Silva16447" /> Later 1988 experiments with more lawrencium atoms refined this to {{val|88.1|0.1|u=pm}} and calculated an [[enthalpy of hydration]] value of {{val|−3685|13|u=kJ/mol}}.<ref name="Silva16447" /> It was also found that the actinide contraction at the end of the actinides was larger than the analogous lanthanide contraction, with the exception of the last actinide, lawrencium: the cause was speculated to be relativistic effects.<ref name="Silva16447" />

It has been speculated that the 7s electrons are relativistically stabilized, so that in reducing conditions, only the 7p<sub>1/2</sub> electron would be ionized, leading to the monovalent {{chem2|Lr(+)}} ion. However, all experiments to reduce {{chem2|Lr(3+)}} to {{chem2|Lr(2+)}} or {{chem2|Lr(+)}} in aqueous solution were unsuccessful, similarly to lutetium. On the basis of this, the [[standard electrode potential]] of the ''E''°({{chem2|Lr(3+) → Lr(+)}}) couple was calculated to be less than −1.56&nbsp;[[volt|V]], indicating that the existence of {{chem2|Lr(+)}} ions in aqueous solution was unlikely. The upper limit for the ''E''°({{chem2|Lr(3+) → Lr(2+)}}) couple was predicted to be −0.44&nbsp;V: the values for ''E''°({{chem2|Lr(3+) → Lr}}) and ''E''°({{chem2|Lr(4+) → Lr(3+)}}) are predicted to be −2.06&nbsp;V and +7.9&nbsp;V.<ref name="Silva16447" /> The stability of the group oxidation state in the 6d transition series decreases as [[rutherfordium|Rf]]<sup>IV</sup> &gt; [[dubnium|Db]]<sup>V</sup> &gt; [[seaborgium|Sg]]<sup>VI</sup>, and lawrencium continues the trend with Lr<sup>III</sup> being more stable than Rf<sup>IV</sup>.<ref>{{cite book| title = The Chemistry of the Actinide and Transactinide Elements| editor1-last = Morss|editor2-first = Norman M.| editor2-last = Edelstein| editor3-last = Fuger|editor3-first = Jean| last1 = Hoffman|first1 = Darleane C.|last2=Lee |first2=Diana M. |last3=Pershina |first3=Valeria |chapter = Transactinides and the future elements| publisher = [[Springer Science+Business Media]]| year = 2006| isbn = 1-4020-3555-1| location = Dordrecht, The Netherlands| edition = 3rd| ref = CITEREFHaire2006| page=1686}}</ref>

In the molecule lawrencium dihydride ({{chem2|LrH2}}), which is predicted to be [[bent molecular geometry|bent]], the 6d orbital of lawrencium is not expected to play a role in the bonding, unlike that of [[lanthanum dihydride]] ({{chem2|LaH2}}). {{chem2|LaH2}} has La–H bond distances of 2.158&nbsp;Å, while {{chem2|LrH2}} should have shorter Lr–H bond distances of 2.042&nbsp;Å due to the relativistic contraction and stabilization of the 7s and 7p orbitals involved in the bonding, in contrast to the core-like 5f subshell and the mostly uninvolved 6d subshell. In general, molecular {{chem2|LrH2}} and LrH are expected to resemble the corresponding [[thallium]] species (thallium having a 6s<sup>2</sup>6p<sup>1</sup> valence configuration in the gas phase, like lawrencium's 7s<sup>2</sup>7p<sup>1</sup>) more than the corresponding [[lanthanide]] species.<ref>{{cite journal|last1=Balasubramanian|first1=K.|date=4 December 2001|title=Potential energy surfaces of Lawrencium and Nobelium dihydrides (LrH<sub>2</sub> and NoH<sub>2</sub>)|journal=Journal of Chemical Physics|volume=116|issue=9|pages=3568–75|bibcode=2002JChPh.116.3568B|doi=10.1063/1.1446029}}</ref> The electron configurations of {{chem2|Lr(+)}} and {{chem2|Lr(2+)}} are expected to be 7s<sup>2</sup> and 7s<sup>1</sup> respectively. However, in species where all three valence electrons of lawrencium are ionized to give at least formally the {{chem2|Lr(3+)}} cation, lawrencium is expected to behave like a typical actinide and the heavier congener of lutetium, especially because the first three ionization potentials of lawrencium are predicted to be similar to those of lutetium. Hence, unlike thallium but like lutetium, lawrencium would prefer to form {{chem2|LrH3}} than LrH, and Lr[[metal carbonyl|CO]] is expected to be similar to the also unknown LuCO, both metals having valence configuration σ<sup>2</sup>π<sup>1</sup> in their monocarbonyls. The pπ–dπ bond is expected to be seen in {{chem2|LrCl3}} just as it is for {{chem2|LuCl3}} and more generally all the {{chem2|LnCl3}}. The complex anion {{chem2|[Lr(C5H4SiMe3)3](−)}} is expected to be stable with a configuration of 6d<sup>1</sup> for lawrencium; this 6d orbital would be [[HOMO/LUMO|its highest occupied molecular orbital]]. This is analogous to the electronic structure of the analogous lutetium compound.<ref name=peculiar>
{{cite journal |last1=Xu |first1=Wen-Hua |last2=Pyykkö |first2=Pekka |date=8 June 2016 |url=http://pubs.rsc.org/-/content/articlehtml/2016/cp/c6cp02706g |title=Is the chemistry of lawrencium peculiar |journal=Phys. Chem. Chem. Phys. |volume=2016 |issue=18 |pages=17351–5 |doi=10.1039/c6cp02706g |pmid=27314425 |access-date=24 April 2017|bibcode=2016PCCP...1817351X |hdl=10138/224395 |s2cid=31224634 |hdl-access=free }}</ref>