Shells, chemical-filled

These two seemingly dissimilar applications have a common basis—both are examples of the pressure-sensitive release of a chemical. How are these products designed Tiny spherical capsules (microcapsules or microspheres) with a glass or polymer shell are filled with a liquid core and glued onto paper. For a scratch-and-sniff ad, the core of the microcapsules contains a liquid with the desired scent for carbonless paper, a liquid ink or dye is encapsulated within the... 

This chapter discusses the range of analytical methods which use the properties of X-rays to identify composition. The methods fall into two distinct groups those which study X-rays produced by the atoms to chemically identify the elements present, and X-ray diffraction (XRD), which uses X-rays of known wavelengths to determine the spacing in crystalline structures and therefore identify chemical compounds. The first group includes a variety of methods to identify the elements present, all of which examine the X-rays produced when vacancies in the inner electron shells are filled. These methods vary in how the primary vacancies in the inner electron shell are created. X-ray fluorescence (XRF) uses an X-ray beam to create inner shell vacancies analytical electron microscopy uses electrons, and particle (or proton) induced X-ray emission (PIXE) uses a proton beam. More detailed information on the techniques described here can be found in Ewing (1985, 1997) and Fifield and Kealey (2000). 

In many chemical reactions, particularly those between the nonmetals, ionization potentials and electron affinities are not large enough to produce ions, and therefore valence shells are filled by the sharing of electrons. In this sharing process, electrons are neither gained nor lost, but become part of the octets of both of the bonded partners. 

The periodic table, described in Section 1.1, was an empirical construction. However, it is fundamentally understandable in terms of the electron configurations just discussed. The chemical and many physical properties of the elements are simply controlled by the valence electrons. The valence electron configuration varies in a systematic and repetitive way as the various shells are filled. This leads naturally to both the periodicity and the repetitive features displayed in the periodic table (Figure 1.9). 

Let us now focus our attention to the outer shells of chemical elements starting from Sc. The 4s shell is filled by electrons whereas 3d shell is not yet filled. It is seen the same for V, Cr, Mn, Fe, Co, Ni. These metals are called the transition metals. 

The later chemical study showed that neptunium was oxidized to hexavalent with the oxidizing agent, bromate ion BrOs it resembled uranium, not rhenium (Re), contrary to the expectation from the periodic table at that time. The result was the first evidence that an iimer electron shell (i.e., the 5f shell) is filled in the transuranium elements. The isotope of neptunium with the longest half-life (Ti/2 = 2.14 x 10 years) is Np, the mother nuclide of the... 

The first shell is filled for helium (He) and all elements beyond, and the second shell is filled for neon (Ne) and all elements beyond. Filled shells play almost no role in chemical bonding. Rather, the outer electrons, or valence electrons, are mainly involved in chemical bonding, and we will focus our attention on them. 

---