KRYPTON.152 PLATINUM

It is the most corrosion-resistant metal known, and was used in making the standard meter bar of Paris, which is a 90 percent platinum and 10 percent iridium alloy. This meter bar was replaced in 1960 as a fundamental unit of length (see under Krypton). 

Krypton difluoride forms complexes with fluorides of many metals, such as arsenic, antimony, tantalum, niobium, gold, and platinum. 

Ferrocene is only one of a large number of compounds of transition metals with the cyclopentadienyl anion. Other metals that form sandwich-type structures similar to ferrocene include nickel, titanium, cobalt, ruthenium, zirconium, and osmium. The stability of metallocenes varies greatly with the metal and its oxidation state ferrocene, ruthenocene, and osmocene are particularly stable because in each the metal achieves the electronic configuration of an inert gas. Almost the ultimate in resistance to oxidative attack is reached in (C5H5)2Co , cobalticinium ion, which can be recovered from boiling aqua regia (a mixture of concentrated nitric and hydrochloric acids named for its ability to dissolve platinum and gold). In cobalticinium ion, the metal has the 18 outer-shell electrons characteristic of krypton. 

Fission gas recoil. Another interesting example of recoil separation in the (n,fisslon) reaction is the separation technique for krypton fission products from a uranium foil target (202). The target, an enriched uranium film (0.3 mg/cm ) deposited on a 1.6-cm diameter platinum plate, was mounted as shown in Fig. 1 at one end of a vacuum-tight recoil chamber... 

Recent experiments by Citrin and coworkers (41) have clarified the role of the support in photoemission from small metal clusters. They condensed several monolayers of krypton onto either platinum or sodium metal substrates. By varying the thickness of the krypton from one to ten monolayers, the surface could be converted from metal to semimetal to insulator. The krypton peak position provides a direct measure of the sample vacuum level (32). The krypton layers are thin, less than 10 monolayers, so that the vacuum level is determined by the metal substrate. Onto the krypton layers, sodium clusters were deposited at varying coverages. Shifts in the Kr 4s and Na 2p binding energies were recorded relative to the Fermi level of the grounded substrate. 

Rhodium hexafluoride forms a deep-red adduct with xenon, the composition of which is close to XeRhFe. Krypton does not react with either platinum hexafluoride or with rhodium hexafluoride at temperatures below 50°. 

Attempts to oxidize krypton with noble-metal hexafluorides.—Platinum hexafluoride and a large krypton excess were separately condensed in a silica bulb. The red vapor of platinum hexafluoride was observed on warm up and was still observable at 50°. 

From the surface areas determined by SEM and Krypton BET the number of sites on the platinum surface can be estimated. This results in 2.7 10" sites for SEM micrographs and 3.1 10" sites for the BET measurement. 

Confirmation of this explanation is unequivocally provided by the presence in the reactor zones of at least half of the more than 30 fission products of uranium. Although soluble salts, such as tho.se of the alkali and alkaline earth metals, have been leached out, lanthanide and platinum metals remain along with traces of trapped krypton and xenon. Most decisively, the observed distribution of the various isotopes of these elements is that of fission products as opposed to the distribution normally found terrestrially. The reasons for the retention of these elements on this particular site is clearly germane to the problem of the long-term storage of nuclear wastes, and is therefore the subject of continuing study. 

Gold, silver, and platinum are members of a class of metals called noble metals because they are relatively unreactive. (The term noble implies a class set apart.) Other elements that appear in nature in the uncombined state are the elements in Group 8 helium, neon, argon, krypton, xenon, and radon. 

Fluorine (F) is one of the most reactive elements and forms chemical bonds with almost all the other elements (with the exception of helium and neon), though it takes higher temperatures to react with noble metals, such as gold, platinum, and palladium. Fluorine can even react with an inert gas (krypton) ... 

Write the correct symbol, with both superscript and subscript, for each of the following. Use the list of elements inside the front cover as needed (a) the isotope of platinum that contains 118 neutrons, (b) the isotope of krypton with mass number 84, (c) the isotope of arsenic with mass number 75, (d) the isotope of magnesium that has an equal number of protons and neutrons. 

As can be concluded from this figure, the apparent ionic radii of La ", the tervalent lanthanides and Ce" " are almost identical to that of The radii of most of the other ions and also of the atoms of the platinum metals are within a range of about 30 M> around the calculated value of the lattice vacancy position thus, one can expect that their incorporation into the lattice will be possible without major difficulties. The same apphes for both the neutral atoms and the tetrava-lent ions of molybdenum and technetium, which means that the question of lattice compatibiUty will give no preference to one of the two valency states. On the other hand, the atomic radii of the fission product noble gases krypton and xenon are... 

Only a few elements occur free in nature. The noble gases—helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn)—occur in air as separate atoms. In addition to occurring in compounds, oxygen (O), nitrogen (N), and sulfur (S) occur in their most common elemental form as the molecules O2, N2, and Sg, and carbon (C) occurs in vast, nearly pure deposits of coal. And some metals—copper (Cu), silver (Ag), gold (Au), and platinum (Pt)—are also sometimes found uncombined. But, aside from these few exceptions, the overwhelming majority of elements occur in compounds, combined with other elements. 

In 1960 it was internationally agreed that the fundamental unit of length, the meter, would be defined in terms of the orange-red spectral line of krypton-86. In fact, 1 meter is exactly 1,650,763.73 wavelengths (in vacuo) of this line. This agreement replaced the standard platinum-iridium meter located in Paris. 

Iridium — (L. iris, rainbow), Ir at. wt. 192.217(3) at. no. 77 m.p. 2446°C b.p. 4428°C sp. gr. 22.42 (17°C) valence 3 or 4. Discovered in 1803 by Tennant in the residue left when crude platinum is dissolved by aqua regia. The name iridium is appropriate, for its salts are highly colored. Iridium, a metal of the platinum family, is white, similar to platinum, but with a slight yellowish cast. It is very hard and brittle, making it very hard to machine, form, or work. It is the most corrosion-resistant metal known, and was used in making the standard meter bar of Paris, which is a 90% platinum-10% iridium alloy. This meter bar was replaced in 1960 as a fundamental unit of length (see under Krypton). Iridium is not attacked by any of the acids nor by aqua regia, but is attacked by molten salts, such as NaCl and NaCN. Iridium occurs uncombined in nature with... 

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