Fourth-period elements

The following are the formulas for some oxides of seven fourth-period elements ... 

Let s begin by surveying some of the key physical and chemical properties of the transition-metal elements and interpreting trends in those properties using the quantum theory of atomic structure developed in Chapter 5. We focus initially on the fourth-period elements, also called the first transition series (those from scandium through zinc in which the 3d shell is progressively filled). Then we discuss the periodic trends in the melting points and atomic radii of the second and third transition series elements. 

FIGURE 8.1 Variation of atomic radii through the fourth-, fifth-, and sixth-period transition-metal elements. Symbols shown are for the fourth-period elements. 

Electronegativity versus atomic number is graphed for the fourth period elements. Describe in words the general trend in electronegativity in Period 4 as atomic number increases. 

Figure 5. Variation in grand mean tetrahedral edge-length with mean ELDP for the second-, third- and fourth-period elements of the periodic table. Used by permission of E. Schweizerbart sche Verlagsbuch-handlung, from Griffen and Ribbe (1979), Neues Jarhrbuch fiir Mineralogie Abhandlungen, Vol. 137, Fig. 6a, p. 65.

So far the nodal structure of the valence s- and p-orbitals themselves has been in our focus, allowing us to explain the special role of the 2p-elements compared to their heavier homologues. The further modulations of chemical and physical properties as we descend to a given group from period 3 on are often summarized under the term secondary periodicity [65, 66]. The main influences here are incomplete screening of nuclear charge by fllled core or semi-core shells and the effects of special relativity. The former reflect shell structure of the atom as a whole and are already important for differences and similarities of the homologous third and fourth period elements, whereas the latter become crucial mainly for the chemistry of the sixth period elements. These aspects have been discussed in detail in various review articles (see, e.g.. Refs [16, 28, 67]), and we, thus, touch them only briefly. 

CH3 )4GeAs(CH3 )3, and (CH3 >3 GeAs(CH3 >4. What will be tbe products if tbe central bonds between the fourth-period elements are broken to yield neutral products Classify these bonds as polar covalent or dative. 

The chemical properties of the transition elements parallel the pattern seen in covalent radii. That is, the fourth-period elements have substantially different properties from the elements in the same group in the fifth and sixth periods. However, elements... 

Most of the transition elements have a doubly filled ns orbital. Because the ns electrons ionize before the (n — l)d electrons, you might expect the +2 oxidation state to be common. This oxidation state is in fact seen in all of the fourth-period elements except scandium, where the 3+ ion with an Ar configuration is especially stable. 

In the 18 elements of the fifth period, sublevels fill in a similar manner as in elements of the fourth period. However, they start at the 5s orbital instead of at the 4s orbital. Successive electrons are added first to the 5s orbital, then to the 4d orbitals, and finally to the 5p orbitals. This can be seen in Figure 3.8. There are occasional deviations from the predicted configurations here also. The deviations differ from those for fourth-period elements, but in each case the preferred configuration has the lowest possible energy. 

The fourth-period element with the largest atom is... 

Nic] Nic, J.P., Zhang, S., Mikkola, D.E., Obervations on the Systematic Alloying of AljTi with Fourth Period Elements to Yield Cubic Phases , Scripta Metall. Mater., 24, 1099-1104... 

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