Bulk elements

Complete qualitative and quantitative bulk elemental analysis of conducting solids to ultratrace levels... 

In a Born-Haber cycle, we imagine that we break apart the bulk elements into atoms, ionize the atoms, combine the gaseous ions to form the ionic solid, then form the elements again from the ionic solid (Fig. 6.32). Only the lattice enthalpy, the enthalpy of the step in which the ionic solid is formed from the gaseous ions, is unknown. The sum of the enthalpy changes for a complete Born-Haber cycle is zero, because the enthalpy of the system must be the same at the start and finish. 

The composition of the Earth was determined both by the chemical composition of the solar nebula, from which the sun and planets formed, and by the nature of the physical processes that concentrated materials to form planets. The bulk elemental and isotopic composition of the nebula is believed, or usually assumed to be identical to that of the sun. The few exceptions to this include elements and isotopes such as lithium and deuterium that are destroyed in the bulk of the sun s interior by nuclear reactions. The composition of the sun as determined by optical spectroscopy is similar to the majority of stars in our galaxy, and accordingly the relative abundances of the elements in the sun are referred to as "cosmic abundances." Although the cosmic abundance pattern is commonly seen in other stars there are dramatic exceptions, such as stars composed of iron or solid nuclear matter, as in the case with neutron stars. The... 

Elements are mostly classified to their abundance in the earth crust. The most abundant elements are known as bulk elements (H, C, N, O, F, Na, Mg, Al, Si, P, S, Cl, K, Ca), the others are considered as trace elements, with the exception of Fe. (Geld-macher-von Mallinckrodt and Meissner 1994). 

Table 1 shows (C/N). The CMK-3 samples r (XPS) than in bulk (elemental analysis) milar, except for the OCM-.N2.00 sample. 

Alternatively, it might be that the underpotentials needed to form atomic layers of the elements were decreasing, shifting closer to the formal potentials for deposition of the bulk elements. This scenario may be a factor, but it is frequently observed that the steady state potentials are more negative then the formal potentials for the elements, where bulk deposits of the elements would be expected to form. 

Chemical elements essential to life forms can be broken down into four major categories (1) bulk elements (H, C, N, O, P, S) (2) macrominerals and ions (Na, K, Mg, Ca, Cl, PO4A SC>4 ) (3) trace elements (Fe, Zn, Cu) and (4) ultratrace elements, comprised of nonmetals (F, I, Se, Si, As, B) and metals (Mn, Mo, Co, Cr, V, Ni, Cd, Sn, Pb, Li). The identities of essential elements are based on historical work and that done by Klaus Schwarz in the 1970s.1 Other essential elements may be present in various biological species. Essentiality has been defined by certain... 

Considering the content of earth s contemporary waters and atmospheres, many questions arise as to the choice of essential elements at the time of life s origins 3.5 billion or more years ago. Certainly, sufficient quantities of the bulk elements were available in primordial oceans and at shorelines. However, the concentrations of essential trace metals in modern oceans may differ considerably from those found in prebiotic times. Iron s current approximate 10 mM... 

XPS spectra were collected for the same petroleum residua and asphaltene samples used in the XANES studies described above. For all samples the total amount of sulfur relative to carbon as measured by XPS was comparable to that determined by bulk elemental analysis. The spectra were deconvoluted by curve fitting, and the approximate quantifications thus derived are shown in Table 111. 

FIGURE 1-12 Elements essential to animal life and health. Bulk elements (shaded orange) are structural components of cells and tissues and are required in the diet in gram quantities daily. For trace elements (shaded bright yellow), the requirements are much smaller for humans, a few milligrams per day of Fe, Cu, and Zn, even less of the others. The elemental requirements for plants and microorganisms are similar to those shown here the ways in which they acquire these elements vary. 

Most metal standards dissolve in 6 M HC1 or HN03 or a mixture of the two, possibly with heating. Frothing accompanies dissolution of metals or carbonates in add, so vessels should be loosely covered by a watchglass or Teflon lid to prevent loss of material. Concentrated HN03 (16 M) may passivate some metals, forming an insoluble oxide coat that prevents dissolution. If you have a choice between using a bulk element or a powder as standards, the bulk form is preferred because it has a smaller surface area on which oxides can form and impurities can be adsorbed. After a pure metal to be used as a standard is cut, it should be etched ( pickled ) in a dilute solution of the add in which it will be dissolved to remove surface oxides and contamination from the cutter. The metal is then washed well with water and dried in a vacuum desiccator. 

Of the elements in the periodic table, 30 have been shown to be essential for microbial growth, although not all of these 30 elements are necessary for the growth and division of every microbial species (Fig. 2). There is an apparent correlation between the abundance of elements in the earth s crust and the nutritional requirements of microbial cells (Wood, 1984). The rates at which elements are cycled in an aqueous environment depends upon the availability of the bulk elements C, H, N, O, P and S (Salomons and Baccini, 1984). 

Not only do microorganisms have a profound influence on the concentration of elements in the atmospheric, aquatic and terrestrial environments (Lovelock, 1979), but the concentration and chemical speciation of these elements predicates which organisms can compete and survive within a given environment. Therefore, the cycling and mobility of trace elements will be linked to the cycling of bulk elements and correlations to the various bulk element cycles can be postulated. 

Elemental Analyses that Include H and O. Unlike C, N, and P, organically bound H and O cannot be measured on aqueous solutions of marine DOM, and accurate elemental analyses that include H and O are only possible if freeze-dried DOM samples contain less than around 5 wt% ash (e.g., residual sea salts). Because of the great difficulty in isolating marine DOM from its seawater matrix, published elemental analyses of marine DOM seldom include H and O. This situation is particularly unfortunate, because the bulk elemental composition of DOM provides substantial insight into its average structural composition (Perdue, 1984), reactivity (Ritchie and Perdue, 2008), bioavailability (Sun et al., 1997), and diage-netic state (Reuter and Perdue, 1984). It is appropriate, therefore, to discuss briefly the important ancillary properties of marine DOM that are derived from bulk elemental compositions that include H and O, if for no other reason than to make the case for the development and implementation of much better methods of isolation of representative, low-ash samples of marine DOM. 

Table I. Bulk Elemental Compositions of Coal Stack Ashesa (11)...

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