Trivalent metal radii

The radius of the second cation in known MuNbOFs, MU2Nb03F3 and Mul2Nb05F compounds containing bi- and trivalent metals, is usually similar to that of niobium s ionic radius. Such compounds cannot be considered as having an island-type structure and will be discussed later on. Only bismuth-containing compounds (Bi3+) display the presence of different cationic sublattices in their crystal structure. 

The replacement of a part of the third component M(II) in the tricomponent system by a trivalent metal cation, M(III), with ionic radius smaller... 

X-ray density and the metallic radius (CN = 12) are calculated to be 1.325 x 104 kg/m3 and 0.177 nm, respectively (119). The metallic radius of berkelium, assuming a metallic valence of 3- and 12-fold coordination, has been calculated to be 0.1739 nm (121). On the other hand, the radii (CN = 12) of berkelium were predicted to be 0.184 nm for trivalent metal and 0.1704 nm for tetravalent metal, so that the observed dhcp form would correspond to tetravalent metal, while the fee form would represent a metallic valence of 3.5 (122). 

In what follows, for more divalent and trivalent metal ions, the effect and the factors on the P dispersion are discussed. Variation of the P dispersion by the binding of six metal ions are shown in Fig. 20. The effect on the P dispersion is systematic. The Tp shifts to higher temperature and the height decreases to lower tan 8 with increasing valencies. The ionic radius appears to relate to the variation of both the radii are Mg < Ca < Zn for... 

Even more striking is the anomalous position of Th in the entropy-radius relationship of Fig. 4. In following the IVA elements, the shift to smaller radius at Hf corresponds to the gross effect of the lanthanide contraction in the previous row. Note that Th is far over into the trivalent metal area, corresponding to a very large radius Ci.e., lower valence for a supposedly tetravalent metal). 

The main criterion for the elements to crystallize in this network is their ionic radius. The ionic radii of various divalent and trivalent metal ions arc given in Table 2. It can be clearly inferred from this table that ions such as Be are too small and ions like Cd arc too large, to be incorporated into HT-like network [31 ]. 

The AE value obtained from the deviation of the g z value from the free spin value increases in order monovalent cations (M ) < divalent cations (M ) < trivalent cations (M )." The AE value also increases with decreasing ion radius when the oxidation state of the metal ion is the same. The same trend has been reported for 02 adsorbed on the surface of various metal oxides, which act as Lewis acids as well. " The scandium ion, which has the smallest ion radius among the trivalent metal cations, gives the largest AE value." ... 

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]. 

Since Lr is a trivalent ion in aqueous solution, it should exhibit a chemical behavior similar to the other 3 -i- actinides and lanthanides, e.g. insoluble fluoride and hydroxide. One would expect Lr to have a slightly smaller ionic radius than Md and to elute before Md from a Dowex 50 cation-exchange resin column using a-hydroxyisobutyric add as eluant (see Fig. 13.1). David et al. have estimated an ionic radius of0.893 A for Lr and a metallic radius of 1.71 A for trivalent Lr [12]. Nugent has calculated values of — 2.0 V for E° (Lr - Lr) and -1-7.9 V for °(Lr " Lr " ) [68]. 

The mixing of di or trivalent metal oxides introduces a great number of anion vacancies. Table 1 (Etsell and Flengas 1970) shows the solubility of rare-earth oxides into Th02. In those rare-earth oxides, scandium oxide shows just a slight solubility because the ionic radius differs greatly between Sc (1.01 A) (Shannon 1976) and Th + (1.19 A) (Shannon 1976). However, yttrium oxide and other rare-earth oxides are quite soluble... 

---