Ionic lanthanides, valence configuration

Symbol Dy atomic number 66 atomic weight 162.50 a lanthanide series, inner transition, rare earth metal electron configuration [Xe]4 5di6s2 atomic volume 19.032 cm /g. atom atomic radius 1.773A ionic radius 0.908A most common valence state +3. 

Symbol Ho atomic number 67 atomic weight 164.93 a lanthanide series rare earth element electron configuration [Xe]4/ii6s2 valence state +3 metallic radius (coordination number 12) 1.767A atomic volume 18.78 cc/mol ionic radius Ho3+ 0.894A one naturally occurring isotope. Ho-165. 

Symbol Lu atomic number 71 atomic weight 174.97 a lanthanide series element an /-block inner-transition metal electron configuration [Xe]4/i45di6s2 valence -1-3 atomic radius (coordination number 12) 1.7349A ionic radius (Lu3+) 0.85A two naturally-occurring isotopes Lu-176 (97.1%) and Lu-175(2.59%) Lu-172 is radioactive with a half-life of 4xl0i° years (beta-emission) several artificial isotopes known, that have mass numbers 155, 156, 167—174, 177—180. 

Symbol Nd atomic number 60 atomic weight 144.24 a rare earth lanthanide element a hght rare earth metal of cerium group an inner transition metal characterized by partially filled 4/ subshell electron configuration [Xe]4/35di6s2 most common valence state -i-3 other oxidation state +2 standard electrode potential, Nd + -i- 3e -2.323 V atomic radius 1.821 A (for CN 12) ionic radius, Nd + 0.995A atomic volume 20.60 cc/mol ionization potential 6.31 eV seven stable isotopes Nd-142 (27.13%), Nd-143 (12.20%), Nd-144 (23.87%), Nd-145 (8.29%), Nd-146 (17.18%), Nd-148 (5.72%), Nd-150 (5.60%) twenty-three radioisotopes are known in the mass range 127-141, 147, 149, 151-156. 

Symbol Pm atomic number 61 atomic weight 145 a lanthanide series inner-transition metal electron configuration [Xe]4/56s2 partially filled f orbitals valence states -i-3 ionic radius Pm " 0.98A aU isotopes of promethium are radioactive twenty-two isotopes in the mass range 134-155 longest-lived isotope Pm-145, ti/2 17.7 year shortest-bved isotope Pm-140, ti/2 9.2 sec. 

Symbol Tb atomic number 65 atomic weight 158.925 a lanthanide series element an inner-transition rare earth metal electron configuration fXe]4/96s2 valence states -i-3, +4 mean atomic radius 1.782A ionic radii, Tb3+... 

Symbol Tm atomic number 69 atomic weight 168.93 a lanthanide series element a rare earth metal electron configuration iXe]4/i36s2 valence +2, -i-3 atomic radius 1.73 A ionic radius, Tm " " 1.09 A for coordination number 7 one stable, natural isotope Tm-169 (100%) thirty radioisotopes in the mass range 146-168, 170-176 ty, 1.92 years. 

The most common oxidation state of the Ln ions is +3, although many divalent and tetravalent species are known. The predominance of trivalent ions can be seen from the electron configurations of these elements Xe Af 5d (>s (n = 0 for La, = 14 for Lu), where successive ionizations of 5d and 6 electrons leave the 4/ electrons as the valence. This also explains the well-known lanthanide contraction, wherein a small ( 16%), yet steady reduction in ionic radii is observed across this series with increasing nuclear charge (36, 37). 

The basis for the family relationships among the lanthanide elements themselves, and of periodic relationships that include the actinide elements, is their elemental and ionic electronic configurations. The fascinating story of the discovery and development of this truth can be found in several chapters in volume 11 of this Handbook on the Physics and Chemistry of Rare Earths (1988) and in the chapter by Seaborg (ch. 118) in this volume. The oxides provide a delicately sculpted model of the relationships between each element and other members of its series and also of the relationships between the two series. The electronic configurations for the ground state of the atoms and the relevant valence states of these elements are listed in table 1. The similarities and lack of congruence for the oxides of these two series is discussed in section 3. 

Ionic compounds which contain lanthanides with a valence 2 or 4 have been known for a long time. These anomalous valence states are due to the stability of certain 4f electronic configurations, namely those of 4f°, 4f and 4f . Compounds containing tetravalent Ce, Pr and Tb and divalent Sm, Eu, Tm and Yb can be prepared. Their abundance and stability are greater for those of Ce, Eu and Yb. Some semimetallic compounds of Sm(II), Tm(II) and perhaps Pr(IV) are known, but the most studied semimetallic and intermetallic compounds are those of Ce, Eu and Yb, which are described in the following. 

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