Transition elements electrode potentials

Other commonly employed redox electrodes are metals such as copper, cobalt, silver, zinc, nickel, and other transition metals. Some p-block metals such as tin, lead and indium can also function as redox electrodes. However, s-block metals such as magnesium do not make good redox electrodes since the elemental metal is reactive and forms a layer of oxide coating, which leads to poor reproducibility, poor electronic conductivity and electrode potentials that are difficult to interpret, (see Section 3.3.1). 

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 Ni atomic number 28 atomic weight 58.693 a transition metal element in the first triad of Group VIll(Group 10) after iron and cobalt electron configuration [Ar]3d 4s2 valence states 0, -i-l, +2, and -f-3 most common oxidation state +2 the standard electrode potential, NF+ -1- 2e Ni -0.237 V atomic radius 1.24A ionic radius (NF+) 0.70A five natural isotopes Ni-58 (68.08%), Ni-60 (26.22%), Ni-61 (1.14%), Ni-62 (3.63%), Ni-64 (0.93%) nineteen radioactive isotopes are known in the mass range 51-57, 59, 63, 65-74 the longest-lived radioisotope Ni-59 has a half-life 7.6x10 years. 

There is a whole gamut of electrochemical methods available for the determination of the transition elements. Electrogravimetric methods are available for large numbers of metals (e.g. Cu, Ag, Cd, Co, Ni, Sn, Zn, Pb, and Tl) provided these are available in weighable amounts. Controlled potential electrolysis at a mercury pool electrode is best suited for separations (e g. Cu, Cd, and Pd from uranium) or removing traces of metalUc impurities when preparing very pure electrolytes for use in polarography. ... 

Solid-state reference electrodes for potentiometric sensors are currently under research. The main problem to be faced in developing this type of electrode lies in connecting the ionic conducting (usually aqueous) solution with an electronic conductor. Since the reference electrode has to maintain a defined potential, the electrochemical reaction with components of the electrolyte has to be avoided. Oxides, mixed oxides, and polyoxometalate salts of transition elements can be proposed for preparing solid-state reference electrodes. Tested compounds include tungsten and molybdenum oxides (Guth et al., 2009). 

Note added in the proof - It was recently been possible (PS) to extend the Inclined W hypothesis in correlating the properties of the -transition elements and their ions with the L-values of the originating ions. We (PS) have examined a variety of plots, such as, the effective ionic radii (high spin and low spin), ionization energies, electrode potentials, B, C and parameters for the free ions, lattice energies, heats of hydration etc. for the 3 d, 4 d and some 5 d cases. In all cases linearity within each tetrad was preserved. 

This series of papers contain critical reviews and selections of thermochemical data for the transition metal elements and their compounds. Tabulated are selected values of A.G , A,H", S , and electrode potentials at 25 C. Each article contains a discussion of the data upon which the selections have been made and the references to the source literature. The papers in the series are ... 

Ionization energies are fairly constant across the first transition series. Values of the first ionization energies are about the same as for the group 2 metals. Standard electrode potentials gradually increase in value across the series. With the exception of the oxidation of Cu to Cu, however, all these elements are more readily oxidized than hydrogen. This means these metals reduce H (aq) to H2(g). Additional comments on electrode potentials, some supported by electrode potential diagrams, are found throughout the chapter. 

Near one metal electrode the potential for a dipole oriented normal to the interface tends to add with that of its image in the metal electrode. The potentials of the dipole and its image tend to cancel for a dipole oriented parallel to the interface. The addition or cancellation of the dipole potential with its image makes it more probable for an inelastic transition to occur for a dipole oriented normal to the interface. Near the center of a tunneling junction, however, the reverse is true for two reasons. 1) The cancellation of potentials for the dipole oriented parallel is least important at the center. 2) The inelastic transition matrix element involves an integration over the barrier volume of the interaction potential times some nearly spatially homogeneous electronic wavefunction terms. If the dipole is oriented normal to the interfaces and located in the center of the barrier, the potential is an odd function in z ( if z defines the normal to the interfaces ), and integrates to... 

Lithium insertion negative electrodes — (i) Some transition-metal oxides or chalcogenides insert Li ion reversibly at low redox potentials, for example, TiC>2, LL I iOy, M0S2, M0O2. (ii) Lithium alloys - in this case lithium ions, react with other elements polarized to low potentials to reversibly form Li alloys. The reaction usually proceeds reversibly according to the... 

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