Atomic radius, rare earth elements

Atomic mass unit (amu), 1-1 to 11,1-23 to 26 Atomic masses, 1-14 to 17,11-56 to 253 Atomic Masses and Abundances, 1-14 to 17 Atomic Radii of the Elements, 9-49 Atomic radius, rare earth elements, 4-127 to 132... 

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. 

The lanthanide contraction is probably the reason why the natural processes lead to fractionation and give rise to cerium group elements containing mainly the larger rare earth elements of lower atomic numbers, and to yttrium earth minerals containing mainly smaller rare earth elements with higher atomic numbers. Yttrium, although not a rare earth element, its atomic number 39 is low and its radius is similar to that of Ho. Thus yttrium appears with heavy rare earth elements. 

A = Alkali metal AE = Alkaline-earth metal a-P = Amorphous phosphorus CN = Mean coordination number (i(M-P) = Distance between M and P atom Distances between P atoms E = Element = Band gap M = Metal PBO = Pauling bond order (P) = Formal charge of a P atom (M) = Formal charge of a M atom R = Zr, Ftf, rare earth metal or actinoid metal RE = Rare earth element / cov = Covalent radius ... 

Use the data from Appendix E to graph the variation of atomic radius with atomic number for the rare-earth elements from lanthanum to lutetium. 

The lanthanide or rare earth elements (atomic numbers 57 through 71) typically add electrons to the 4f orbitals as the atomic number increases, but lanthanum (4f°) is usually considered a lanthanide. Scandium and yttrium are also chemically similar to lanthanides. Lanthanide chemistry is typically that of + 3 cations, and as the atomic number increases, there is a decrease in radius for each lanthanide, known as the lanthanide contraction. Because bonding within the lanthanide series is usually predominantly ionic, the lanthanide contraction often determines the differences in properties of lanthanide compounds and ions. Lanthanide compounds often have high coordination numbers between 6 and 12. see also Cerium Dysprosium Erbium Europium Gadolinium Holmium Lanthanum Lutetium Praseodymium Promethium Samarium Terbium Thulium Ytterbium. 

The rare earth elements (REE) are the most useful of all trace elements and REE studies have important applications in igneous, sedimentary and metamorphic petrology. The REE comprise the series of metals with atomic numbers 57 to 71 — La to Lu (Table 4.4). In addition, the element Y with an ionic radius similar to that of the REE Ho is sometimes included. Typically the low-atomic-number members of the series are termed the light rare earths (LREE), those with the higher atomic... 

Yttrium has geochemical behavior very similar to the lanthanides, which is why it is considered to be a REE. Scandium, however, shows geochemical behavior that is much more similar to that of the ferromagnesian transition elements (Fe, V, Cr, Co and Ni), due to its smaller atomic radius. This is also due to a different coordination in the crystal lattices of minerals. Therefore, scandium is often considered not to be a rare earth element, but a ferromagnesian trace element. In aqueous systems, however, scandium behaves more like the other REEs (McLennan 2012). 

Also as a result of the lanthanide contraction, yttrium has an ionic radius comparable to that of the heavier REE species in the holmium-erbium region. If the effective ionic radius (Shannon 1976) of is plotted (0.90 A)., it plots in between element 67 (Ho) and 68 (Er). Scandium (effective ionic radius is 0.745 A), plots outside of the Lanthanide series. As also the outermost electronic arrangement of yttrium is similar to the heavy rare earths, the element behaves chemically like the heavy rare earths. It concentrates during (geo)chemical processes with the heavier REEs, and is difhcult to separate from the heavy REEs. Scandium, on the other hand, has a much smaller atomic radius, and the trivalent ionic size is much smaller than that of the heavy rare earths. Therefore, scandium does not occur in rare earth minerals, and in general has a chemical behavior that is significantiy different from the other rare earth elements (Gupta and Krishnamurthy 2005). 

Figure 1 Plot of ionic radius versus atomic number for the trivalent lanthanide elements (La-Lu). Also shown are the ionic radii for trivalent Y and Sc, for the Eu + and Ce +, and for other selected cations. The regular decrease in the ionic radii of the trivalent lanthanides is part of the lanthanide contraction. Sc is much smaller than the other rare earth elements and more similar in size to Fe + and Mg +...

One of the reasons to use other systems is that the systems proposed by Pauling were not complete. The data of many elements such as rare earth elements and actinide elements were absent. The description of the chief systems of atomic or ionic radius will be given as follows ... 

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 La atomic number 57 atomic weight 138.91 a rare-earth transition metal, precursor to a series of 14 inner-transition elements known as the lanthanide series electron configuration [XejSdiGs oxidation state -i-3 atomic radius 1.879A ionic radius (LaS+) 1.061A electronegativity 1.17 two natural isotopes are La-139 (99.911%) and La-138 (0.089%). 

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 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. 

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