Editing Alkali metal (section)

==== Francium ====
Francium is also predicted to show some differences due to its high [[atomic weight]], causing its electrons to travel at considerable fractions of the speed of light and thus making [[relativistic effects]] more prominent. In contrast to the trend of decreasing [[electronegativities]] and [[ionisation energies]] of the alkali metals, francium's electronegativity and ionisation energy are predicted to be higher than caesium's due to the relativistic stabilisation of the 7s electrons; also, its [[atomic radius]] is expected to be abnormally low.<!--Haire says this happens for Uue because of the analogous effect for 8s – seems likely for Fr too--> Thus, contrary to expectation, caesium is the most reactive of the alkali metals, not francium.<ref name="andreev" /><ref name="Uue">{{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 |year= 2006 |isbn= 978-1-4020-3555-5 |location= Dordrecht, The Netherlands |edition= 3rd }}</ref>{{rp|1729}}<ref name=Thayer /> All known physical properties of francium also deviate from the clear trends going from lithium to caesium, such as the first ionisation energy, electron affinity, and anion polarisability, though due to the paucity of known data about francium many sources give extrapolated values, ignoring that relativistic effects make the trend from lithium to caesium become inapplicable at francium.<ref name=Thayer /> Some of the few properties of francium that have been predicted taking relativity into account are the electron affinity (47.2 kJ/mol)<ref name=Landaualkalis>{{cite journal |last1= Landau |first1= A. |last2= Eliav |first2= E. |last3= Ishikawa |first3= Y. |last4= Kaldor |first4= U. |year= 2001 |title= Benchmark calculations of electron affinities of the alkali atoms sodium to eka-francium (element 119) |url= https://www.academia.edu/20466410 |journal= J. Chem. Phys. |volume= 115 |issue= 6 |page= 2389 |doi= 10.1063/1.1386413 |bibcode= 2001JChPh.115.2389L |archive-date= 31 July 2020 |access-date= 16 November 2016 |archive-url= https://web.archive.org/web/20200731131615/https://www.academia.edu/20466410/Benchmark_calculations_of_electron_affinities_of_the_alkali_atoms_sodium_to_eka-francium_element_119_ |url-status= live }}</ref> and the enthalpy of dissociation of the Fr<sub>2</sub> molecule (42.1 kJ/mol).<ref name=Liddle>{{cite book |last1=Jones |first1=Cameron |last2=Mountford |first2=Philip |last3=Stasch |first3=Andreas |last4=Blake |first4=Matthew P. |editor-last=Liddle |editor-first=Stephen T. |title=Molecular Metal-Metal Bonds: Compounds, Synthesis, Properties |publisher=John Wiley and Sons |date=22 June 2015 |pages=23–24 |chapter=s-block Metal-Metal Bonds |isbn=978-3-527-33541-1}}</ref> The CsFr molecule is polarised as Cs<sup>+</sup>Fr<sup>−</sup>, showing that the 7s subshell of francium is much more strongly affected by relativistic effects than the 6s subshell of caesium.<ref name=Thayer /> Additionally, francium superoxide (FrO<sub>2</sub>) is expected to have significant covalent character, unlike the other alkali metal superoxides, because of bonding contributions from the 6p electrons of francium.<ref name=Thayer />