Berkelium electronic structure

The higher actinide metals americium, curium, berkelium and californium have - at normal pressure - again the common structure dhcp and are in this respect similar to some of the lanthanide metals. In fact, the theoretical calculations and certain experimental observations show that in these actinide metals, 5 f electrons are localized, as are the 4f electrons in the lanthanide metals. More detailed considerations on the possible correlations between electronic and crystal structure are found in. ... 

The ground-state electronic configurations (levels) of neutral and singly ionized berkelium were identified as 5f 7s2 (6H15/2) and Sf s1 (7H8), respectively (82). A nuclear magnetic dipole moment of 1.5 nuclear magnetons (61) and a quadrupole moment of 4.7 barns (83) were determined for 249Bk, based on analysis of the hyperfine structure in the berkelium emission spectrum. 

The electronic configurations 5f or 4f representing the half-filled f shells of curium and gadolinium, have special stability. Thus, tripositive curium and gadolinium, are especially stable. A consequence of this is that the next element in each case readily loses an extra electron through oxidation, so as to obtain the f structure, with the result that terbium and especially berkelium can be readily oxidized from the III to the IV oxidation state. Another manifestation of this is that europium (and to a lesser extent samarium) -just before gadolinium - tends to favor the 4f structure with a more stable than usual II oxidation state. Similarly, the stable f electronic configuration leads to a more stable than usual II oxidation state in ytterbium (and to a lesser extent in thuUum) just before lutetium (whose tripositive ion has the 4f structure). This leads to the prediction that element 102, the next to the last actinide element, will have an observable II oxidation state. 

Actinium and thorium have no / electrons and behave like transition metals with a body-centered cubic structure of thorium. Neptunium and plutonium have complex, low-symmetry, room-temperature crystal structures and exhibit multiple phase changes with increasing temperature due to their delocalized 5/ electrons. For plutonium metal, up to six crystalline modifications between room temperature and 915 K exist. The / electrons become localized for the heavier actinides. Americium, curium, berkelium, and californium all have room-temperature, double hexagonal, close-packed phases and high-temperature, face-centered cubic phases. Einsteinium, the heaviest actinide metal available in quantities sufficient for crystal structure studies on at least thin films, has a face-centered cubic structure as typical for a divalent metal. 

In 1972 a hybridized non-degenerate 6d and 5f virtual-bound-states model was used to describe the properties of the actinide metals, including berkelium [138]. It accounted for the occurrence of localized magnetism in Bk metal. In 1974 a review of the understanding of the electronic properties of berkelium metal as derived from electronic band theory was published [139]. Included was the relativistic energy band structure of face-centered cubic Bk metal (5f 6d 7s ), and the conclusion was that berkelium is a rare-earth-like metal with localized (ionic) 5f electrons resulting from less hybridization with the 6d and 7s itinerant bands than occurs in the lighter actinides. 

A phenomenological model based on crystal structure, metallic radius, melting point, and enthalpy of sublimation has been used to arrive at the electronic configuration of berkelium metal [140]. An energy difference of 0.92 eV was calculated between the 5f 7s ground state and the 5f 6d 7s first excited state. The enthalpy of sublimation of trivalent Bk metal was calculated to be 2.99 eV (288 kJmol ), reflecting the fact that berkelium metal is more volatile than curium metal. It was also concluded that the metallic valence of the face-centered cubic form of berkelium metal is less than that of the double hexagonal close-packed modification [140]. 

---