Metallic lanthanides valence configuration

Except for helium, the number of valence electrons in an atom is the same as the group number of the element. For example, Li is a Group lA element and has one dot for one valence electron Be, a Group 2A element, has two valence electrons (two dots) and so on. Elements in the same group have similar outer electfon configurations and hence similar Lewis dot symbols. The transition metals, lanthanides, and actinides all have incompletely filled inner shells, so we generally cannot write simple Lewis dot symbols for them. 

Chemical bonding involves only the valence electrons, which are usually the electrons in the outermost occupied shells. In Lewis dot representations, only the electrons in the outermost occupied r and p orbitals are shown as dots. Table 7-1 shows Lewis dot formulas for atoms of the representative elements. All elements in a given group have the same outer-shell electron configuration. It is somewhat arbitrary on which side of the atom S)mibol we write the electron dots. We do, however, represent an electron pair as a pair of dots and an unpaired electron as a single dot. Because of the large numbers of dots, such formulas are not as useful for compounds of the transition metals, lanthanides, and actinides. 

A number of other examples of relativistic effects in transition metal compounds may be found in the calculations by Balasubramanian and coworkers (Balasubramanian 1997b). For the lanthanides and actinides, the situation becomes rather more complex. With a valence configuration of s d f" for the early actinides, these compounds are also strongly infiuenced by the spin-free relativistic effects. We refer the reader to the literature for a further discussion of these effects (Dolg 2002). 

Metals with a d f" configuration, group 3 metals, lanthanides, and actinides, are usually classified as f-elements. Because they are highly electropositive, they form polarized bonds with p-block elements, including carbon and nitrogen. So far, two reaction mechanisms have been established for d f metals cr-bond metathesis, a 2o—2o process, and 1,2-addition, a [2ct—2jt] process (2cr stands for the two electrons involved in the transition state that come from a tr bond and 2jt indicates the two electrons involved in the transition state that come from a Jt bond) (Scheme 1). " Oxidative addition, another type of reaction mecharusm that is common for late transition metals, is absent from the chemistry of rare-earth metals or actinides. This is partly because of the lack of valence electrons, i.e., a d electronic configuration however, even for uranium, which has multiple accessible oxidation states, no genuine oxidative addition reactivity has been reported. The subject of C—H bond activation mediated by f-elements has been dis-cussed by several recent reviews. ... 

Symbol Ce atomic number 58 atomic weight 140.115 a rare-earth metal a lanthanide series inner-transition /-block element metaUic radius (alpha form) 1.8247A(CN=12) atomic volume 20.696 cm /mol electronic configuration [Xe]4fi5di6s2 common valence states -i-3 and +4 four stable isotopes Ce-140 and Ce-142 are the two major ones, their percent abundances 88.48% and 11.07%, respectively. Ce—138 (0.25%) and Ce—136(0.193%) are minor isotopes several artificial radioactive isotopes including Ce-144, a major fission product (ti 284.5 days), are known. 

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 Eu atomic number 63 atomic weight 151.97 a lanthanide group inner transition metal electron configuration [Xe]4/ 5di6s2 (partially filled orbitals) valence states +3 and +2. 

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 lanthanide elements are differentiated from other metallic elements by the fact that their valence electrons are in 4/ orbitals. Calculations on the [Xe]4/" electron configurations of the lanthanides indicate that the 4/... 

Compared with the lanthanides or the transition metals, the actinide elements introduce a striking array of novel chemical features, displayed most clearly in the chemistry of uranium. There is the variety of oxidation state, and to some extent the chemical diversity, typical of transition metals in the same periodic group, but physical properties which show that the valence electrons occupy /-orbitals in the manner of the lanthanides. This raises the question of the nature of the chemical bond in the compounds of these elements. The configuration of the uranium atom in the gas phase is f3ds2, so it is natural to ask whether there are special characteristics of the bonding that reflect the presence of both/and d valence orbitals. 

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