Vanadium radii

Explain why vanadium (radius = 134 pm) and copper (radius = 128 pm) have nearly identical atomic radii, even though the atomic number of copper is about 25% higher than that of vanadium. What would you predict about the relative densities of these two metals Look up the densities in a reference book, periodic table, or on the Web. Are your predictions correct ... 

Vanadium crystallizes with a body-centered cubic unit cell. The volume of the unit cell is 0.0278 nm3. What is its atomic radius ... 

Valence, 286 Valence electrons, 269 and ionization energies, 269 Vanadium atomic radius, 399 eleciron configuration, 389 oxidation numbers, 391 pentoxide catalyst, 227 properties, 400, 401 van der Waals forces, 301 elements that form molecular crystals using, 301 and molecular shape, 307 and molecular size, 307 and molecular substances, 306 and number of electrons, 306 van der Waals radius, 354 halogens, 354 Vanillin, 345... 

Identify the element with the larger atomic radius in each of the following pairs (a) vanadium and titanium (b) silver and gold (c) vanadium and tantalum (d) rhodium and iridium. 

Arrange the elements in the following sets in order of decreasing atomic radius (a) lithium, carbon, fluorine (b) scandium, vanadium, iron (c) iron, ruthenium, osmium (d) iodine, bromine, chlorine. 

Calculate the atomic radius of the following elements from the data given (a) gold (fee structure, density 19.3 g-cm-3) (b) vanadium (bcc structure, density 6.11 g-cm-3). 

Figure 7 shows the influence of the initial pore radius, in the case of a wide- and narrow-pore silica catalyst, on the vanadium deposition profiles at an average axial position in the reactor. Both cases show the presence of deposition maxima, indicating that the deposition process is diffusion rate-limited. In the case of the narrow-pore silica the core volume of the pellet potentially available for vanadium deposition cannot be reached by reactant and intermediates and is lost for vanadium deposition. 

Figure 5. Influence of the bulk difftision coefficient, D, on the vanadium deposition profile in a wide pore silica catalyst pellet at reactor inlet conditions. (Model compound VO-TPP, 673 K, 10 MPa H2, initial pore radius 30 nm, catalystpellet radius 0.85 mm)...

Figure 7. Influence of the initial pore radius on the vanadium deposition profile (wide- and narrow pore silica catalyst pellet) at an average axial position in the reactor.

Figure 8. Experimental vanadium deposition profiles for wide- and narrow pore silica catalyst. (Industrial feedstock containing 61 ppm V, 673 K, 15 MPa H2, catalyst pellet radius 0.85 mm)...

Figure 1 shows measured Peak shifts (Peak shift is defined as the distance from the particle edge to the point of maximum Vanadium concentration, expressed as a fraction of the particle radius) for various catalysts vs. fractional distance from the top to the reactor. Qualitatively, the results are in full agreement with the theory that predicts ... 

The initial coking also has some interesting indicators for metals distribution in the catalyst, as can be illustrated using data reported by Tamm et al [20]. They found that nickel distribution in pellets at the inlet and the outlet of the reactor passed through a maximum across the fractional radius of the pellet. Near the inlet, the maximum deposition was some distance inside the pellet, as opposed to vanadium which was deposited predominantly at or near the external surface. Similar observations have been observed by others [21, 22]. 

A similar phenomenon has been observed by the author and Sokolova, 189) for the catalysis of alcohols on pentoxides of vanadium, niobium and tantalum. The increase of dehydration as against dehydrogenation goes on simultaneously with the increase of the atomic radius in the series vanadium (1.36 A) niobium (1.47 A) tantalum (1.49 A.)... 

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