Mendeleev number

In the same chapter (Chapter 5), as an introduction to the paragraphs dedicated to the various groups of metals, the values relevant to a number of elementary properties have been collected. These are atomic properties (such as metallic and ionic radii, ionization energies, electronegativities, Mendeleev number, chemical scale, Miedema parameters, etc.), crystal structure and lattice parameters data of the allotropes of the elements, and selected thermodynamic data (melting and boiling temperatures and enthalpies, etc.). All these data indeed represent reference values in the discussion of the alloying behaviour of the elements. 

Electronegativity, Mendeleev number, Miedema parameters. A few semi-empirical parameters and scales which are useful as reference data in the systematic description (or even prediction) of the alloying behaviour of the different metals will be presented here also as an introduction to the following paragraphs. The closely related basic concepts of chemical periodicity and electron configurations will be reminded in Chapter 4. 

Electronegativity and the so-called Mendeleev number are two parameters, basically empirical at least in their initial definitions, which, however, proved to be very... 

Figure 2.5. Simplified version of Pettifor s map for AB compounds. The component elements are arranged along the axes according to their Mendeleev number (M). As an example, the existence regions of the NaCl, CsCl and cubic ZnS type phases are evidenced.

Figure 2.17. Liquid-liquid and solid-gas equilibria in intermetallic systems. In a map based on the so-called Mendeleev number coordinates the different binary combinations are represented. Only those combinations have been coded for which the existence of liquid miscibility gaps (or of solid-gas equilibria) is known. (In the same systems, other equilibria, the formation of compounds, etc. may be present). For many systems data are lacking probably in the bottom-left comer of the figure many more boxes could be added to those representing miscibility gap. Notice that the solid-gas equilibria are relevant to systems formed by metals with a large difference between their boiling temperatures.

In Figs. 2.22 and 2.23 all the binary combinations are mapped as a function of the Mendeleev numbers of the two elements involved. The compound formation capability is represented in Fig. 2.22 by means of a few codes, whereas in Fig. 2.23 an indication is given of the thermal stability of the intermediate phases. To this end, values correlated to the so-called Raynor Index (Raynor 1972, 1974) are coded in this figure. 

Figure 2.22. Compound formation capability in binary systems. The different element combinations are mapped on Mendeleev number coordinates and those systems are indicated in which the formation of intermediate phases has been observed (either from the liquid or in the solid state). Blank boxes indicate systems for which no certain data are available. Notice that the compound-forming alloys are crowded in a region corresponding to a large difference in the Mendeleev numbers of the elements involved (for instance, basic metals with semi-metals).

On the basis of the Periodic Table, topics of intermetallic systematics will be presented in the next chapter. In the present chapter the Periodic Table will be revisited and its structure and subdivisions summarized. In relation also to some concepts previously presented, such as electronegativity, Mendeleev number, etc. described in Chapter 2, typical property trends along the Table will be shown. Strictly related concepts, such as Periodic Table group number, average group number and valence-electron number will be considered and used in the description and classification of intermetallic phase families. 

Some aspects of the mentioned relationships have been presented in previous chapters while discussing special characteristics of the alloying behaviour. The reader is especially directed to Chapter 2 for the role played by some factors in the definition of phase equilibria aspects, such as compound formation capability, solid solution formation and their relationships with the Mendeleev Number and Pettifor and Villars maps. Stability and enthalpy of formation of alloys and Miedema s model and parameters have also been briefly commented on. In Chapter 3, mainly dedicated to the structural characteristics of the intermetallic phases, a number of comments have been reported about the effects of different factors, such as geometrical factor, atomic dimension factor, etc. on these characteristics. 

An extension of the application of these maps to the systematic description of certain groups of ternary alloys has been presented also by Pettifor (1988a, b). Composition averaged Mendeleev numbers can be used, for instance, in the description of pseudo-binary, ternary or quaternary alloys. All these maps show well-defined domains of structural stability for a given stoichiometry, thus making the search easier for new ternary or quaternary alloys with a particular structure type (and which, as a consequence, may have the potential of interesting properties and applications (Pettifor 1988a, b)). 

This chapter describes typical aspects of the alloying behaviour of the different metals, with reference to the general topics previously discussed. The metals will be considered according to their order in the Periodic Table and to their reactivity towards the other elements. The Pettifor scale and the so-called Mendeleev number have been used in previous chapters as an introduction to some aspects of the alloying systematics. 

Figure 3 The Pettifor single string rearrangement of the Periodic Table in the sequence of the Mendeleev Number...

Figure 5 Experimental (solid squares) and calculated (open circles and stars) enthalpies of formation of nitrides of the transition metals in the cubic-NaCI and hexagonaT ZnS structures plotted as a function of the Mendeleev Number...

After some thought, Mendeleev numbered the columns with Roman numerals, some with the letter "A" and some with the letter "B."This system was used virtually unchanged until quite recently, when minor variation between U.S. and European chemists (A/B variation) forced the international chemistry organization to recommend a column numbering system from 1-18, moving from left to right. In columns 1, 2, and 13-18, a number of elements extend above the rest. These elements are referred to as representative elements. The elements found in columns 3-12 are classified as transition elements. At the bottom of the periodic table are two rows that appear to be separated from the main body of the table. This is for convenience only. Elements 58-71 and 90-103 are called inner transition elements and actually fit between columns 3 and 4. 

In Figure 1.1, the Groups are numbered in two different ways. In the Mendeleev numbering scheme, which is given in Roman numerals, the Group numbers increase smoothly across each row from I to VIII. These numbers are useful because, for each element, they are almost always equal to the number of outer electrons in the atom, and to the highest oxidation state (see Section 2.1) that is reached in the compounds that the element forms. Use is made of these relationships in this Book. 

Figure 1.2 The arrangement of the typical elements and transition elements in a Periodic Table that generates the lUPAC numbering. The Mendeleev numbering is also shown.

---