Terbium electronic structure

The table "Electronic Structure of Isolated Atoms," unlike similar tables as usually published, includes some refinements and additions in accordance with work done in recent years in particular the electronic configuration of the terbium atom has been refined. The table also gives the electronic structures proposed for the elements with atomic numbers from 98 to 103. 

FIGURE 29 Equation of state fit for terbium to 155 GPa. At 51 2 GPa, a 5% volume collapse is observed as the structure transforms to the open, low symmetry C2/m phase. The sharp decrease in compressibility of this low symmetry phase is argued as an indication of change in character of metallic bonds, that is, onset of 4f electron participation in bonding (Cunningham et al., 2007). 

FIGURE 45 The transition pressures for selected lanthanides which exhibit monoclinic (C2/m) structure as a o i-dfcc phase. The solid line is only a guide to the eye and it indicates that die pressure needed to delocalize 4f electrons increases with increasing atomic number. Terbium is an exception (see text and summary). 

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. 

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