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GADOliNIUM Gadolinium (Gd) is a silvery-white metal with an atomic number (Z) of 64, electronic configuration of [Xe]4f15d 16s 2 , atomic weight of 157.25 and melting point of 1586 K. It is a Group IIIB inner transition element and one of the lanthanide and rare earth elements. Gadolinium has seven natural isotopes, 152 Gd (0.20%), 154 Gd (2.15%), 155 Gd (14.73%), 156 Gd (20.47%), 157 Gd (15.68%), 158 Gd (24.87%) and 160 Gd (21.90%). The isotope 152 Gd is radioactive with a half life (T 112 ) of 1.1 x 10 14 years. Discovered in 1880, Gd is named after the mineral gadolinite, which in turn is named after the Finnish chemist J. Gadolin. Gadolinium is typically a trace element in most rocks and minerals. It is refractory and under most conditions is lithophile and found in the trivalent state. The major importance of Gd in geochemistry is that it is one of the middle trivalent rare earth elements (or lanthanides), among the most useful trace elements in all areas of geochemistry and cosmochemistry due to their coherent and systematic behavior as a group. Scott M. McLennan Cross-references Elements: Elements: Elements: Elements:
lanthanide series, rare earths large ion lithophile lithophile trace
GALLIUM: ELEMENT AND GEOCHEMISTRY
Atomic number Atomic weight Isotopes and abundances (%) Mass No. 69 71
Metal Crystal structure Density (g/cm 3 ) Melting point CCC) Boiling point CCC) Electron configuration Electrode potential for GaH(V) (Ga3+ + 3e- = Ga 0 , H 2 = 0.0) Ionic radius for Ga3+ (pm) Ionization for GaH (kJjmol) Electronegativity (after Pauling) Ionic potential for Ga 3+
31 69.72
60.4 39.6 orthorhombic 5.904 29.78
2403 [Ar]3d 104s 24p 1 -0.56 62 2962.3
1.7 4.8
No significant differences in the isotopic ratios of meteoritic and terrestrial materials have been observed. Gallium shows high affinity to aluminum. Some differences, however, are important in nature. The reduction to the elementary state needs less energy than in the case of aluminum. The gallium halogenides are more volatile. Gallium can occur in the monovalent state, like the other heavier elements of the group indium and thallium, but the Ga + ion is unstable. Gallium has stronger acidic properties, so that Ga(OH) 3 precipitates at pH 3.4 compared to Al(OHh at pH 4.1. The stronger Ga-S bond enables the formation of stable sulfides. Gallium also tends to form organometallic complexes, unlike aluminum.
Properties
Crystal chemistry
The predicted eka-aluminum was detected as new element in 1875 by Lecoq de Boisbaudron by means of optical spectroscopy in sphalerite from Pierrefitte (Pyrenees). It was named gallium (Latin term for France). The chemical symbol is Ga. The physical properties are described in Table G I. Two stable isotopes and ten short-lived radioactive isotopes are known.
The geochemical coherency of gallium and aluminum is very high. Compared to aluminum, Ga 3 + has the larger ionic radius, higher electronegativity and ionization potential. The Ga-O bond is longer and more covalent. Therefore, GaH shows a tendency to octahedral c
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