Iron-group elements

The whole question is clarified when considered in relation to the foregoing quantum mechanical treatment of the electron-pair bond. For the iron-group elements the following rules follow directly from that treatment and from the rules of line spectroscopy. 

Refractory materials in primitive meteorites were investigated first as they have the best chance of escaping homogenization in the early solar system. Inclusions in C3 carbonaceous chondrites exhibit widespread anomalies for oxygen and the iron group elements. Only a few members, dubbed FUN (for Fractionated and Unknown Nuclear effects), also display anomalous compositions for the heavy elements. Anomalies in inclusions have generally been connected with explosive or supernova nucleosynthesis. 

The iron group elements (from calcium to zinc). Some typical results on this group of elements are displayed in Figure 2. This group of elements have the most stable nuclei of the... 

The iron group elements. Figure 3 displays the isotope ratios for this group. As a general result, the most neutron-rich isotope nuclei of this group display the largest variations relative to the other isotopes. Deficits are seen for Cl, and excesses for EK141. 

The papers dealing with the iron group elements exchanged in zeolites will be discussed in Section IV,C,3. 

After 2 billion years, when stars of <8 M began to reach the end of their lifetimes, type la supemovae began to contribute to the elemental budget of the galaxy. Because a type la supernova completely dismpts the star, it efficiently ejects iron-group elements. The iron group elements thus built up more slowly than the elements from carbon to titanium. 

The magnetic method cannot be applied to tripositive chromium, the structures of the two extreme types having the same number of unpaired electrons and entering into resonance with each other. The chemical properties of the chromium complexes indicate that chromium, like the other iron-group elements, forms hyperligating bonds... 

The discovery that the iron-group elements can form bonds which have in part the character of multiple bonds by making use of the orbitals and electrons of the 3d subshell, whilq surprising, need not be greeted with skepticism the natural formula for a compound ECO is that with a double bond from R to C, and the existence of the metal carbonyls might well have been interpreted years ago as evidence for double-bond formation by metals. The double-bond structure for nickel tetracarbonyl (structure E) was in fact first proposed by Langmuir62 in 1921, on the basis of the electroneutrality principle, but at that time there was little support for the new idea. 

Van Santen, J. II. and J. S. van W icringen Some Remarks on the Ionic Radii of Iron-Group Elements. The Influence of Crystalline Field. Rec. Trav. Chim. 77, 420 (1952). 

Silicon is composed of three stable isotopes, masses 28, 29 and 30, and is one of the cornerstone elements of nucleosynthesis theory. Thermal decomposition of its nuclei after first becoming dominant in the cores of stars and its subsequent reassembly into iron-group elements is called silicon burning in stellar evolution and nucleosynthesis. That process is important for understanding how supernova explosions assemble the relative abundances of the elements having masses between... 

Table 1 Hydrostatic nuclear burning stages in massive stars. The table gives burning stages, main and secondary products (ashes), typical temperatures and burning timescales for a 20M star, and the main nuclear reactions. An ellipsis ( ) indicates more than one product of the double carbon and double oxygen reactions, and a chain of reactions leading to the buildup of iron group elements for silicon burning.

The p-process is one of proton capture (p,y) or of gamma-ray absorption with neutron emission (y,n), and is responsible for many proton-rich nuclides of low abundance, generally derived from iron-group elements. Finally, an x-process is responsible for the synthesis of D, Li, Be and B which are unstable at the temperatures reached inside stars, where they are converted to helium by a large number of processes including 2D(p.y) He, Li(p,a) He and iiB(p,a)8Be -> 2 He. 

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