Atomic properties transition elements

The redox behaviour of Th, Pa and U is of the kind expected for d-transition elements which is why, prior to the 1940s, these elements were commonly placed respectively in groups 4, 5 and 6 of the periodic table. Behaviour obviously like that of the lanthanides is not evident until the second half of the series. However, even the early actinides resemble the lanthanides in showing close similarities with each other and gradual variations in properties, providing comparisons are restricted to those properties which do not entail a change in oxidation state. The smooth variation with atomic number found for stability constants, for instance, is like that of the lanthanides rather than the d-transition elements, as is the smooth variation in ionic radii noted in Fig. 31.4. This last factor is responsible for the close similarity in the structures of many actinide and lanthanide compounds especially noticeable in the 4-3 oxidation state for which... 

There are two immediate questions we ask about the transition elements once we know where they are in the periodic table (1) Why do we consider these elements together (2) What is special about their properties These questions are closely related because they both depend upon the electron configurations of the atoms. What, then, is the electron configuration we might expect for these elements ... 

What properties do we actually find for the transition elements What kinds of compounds do they form How can the properties be interpreted in terms of the electron populations of the atoms ... 

The Niccolite Structure. The substances which crystallize with the niccolite structure (B8) are compounds of transition elements with S, Se, Te, As, Sb, Bi, or Sn. The physical properties of the substances indicate that the crystals are not ionic, and this is substantiated by the lack of agreement with the structural rules for ionic crystals. Thus each metal atom is surrounded by an octahedron of non-metal atoms but these octahedra share faces, and the edges of the shared faces are longer than other edges (rather than shorter, as in ionic crystals). Hence we conclude that the bonds are covalent, with probably some metallic character also. 

In the papers referred to above it is pointed out that the mechanical properties of the transition elements and the distances between atoms in metals and intermetallic compounds are well accounted for by these considerations. In the following sections of the present paper a discussion is given of the number of valence electrons by the Brillouin polyhedron method, and it is shown that the calculations for the filled-zone alloys such as the 7-alloys provide further support for the new system of metallic valences. 

As can be seen from Table 1, not only the spectral data are quite different between pairs of compounds, but also the paramagnetism is decreasing when the carbon atom attached to the nitrogen is replaced by silicon, all other atoms being equal. As we have not been able to determine the molecular structures of the compounds until now, we cannot ascribe the change in properties to a definite change in structure. Nevertheless it seems obvious that the carbon or silicon atom in 6-position to the metal must have an important impact on the orbital-splitting at the transition element. 

The number of electrons in the outer shell of each atom determines most of an element s chemical properties. Since the outer shell is not changing, many transition elements are similar to one another. They are all metals. Some are the familiar metals of cars and coins and rocket ships. Others are rare and seldom used. This large group contains over half the total number of elements. 

The principal characteristic of the transition elements is an incomplete electronic subshell that confers specific properties on the metal concerned. Ligand systems may participate in coordination not only by electron donation to the 3d levels in the first transition series but also by donation to incomplete outer 4s and 4p shells. Figure 5.1 shows that the differences in orbital energy levels between the 4s, 4p and 3d orbitals are much smaller than, for example, the difference between the inner 2s and 2p levels. Consequently, transitions between the 4s, 4p and 3d levels can easily take place and coordination is readily achieved. The manner in which ligand groups are oriented in surrounding the central metal atom is determined by the number and energy levels of the electrons in the incomplete subshells. 

Magnetic Properties of Atomic Clusters of the Transition Elements... 

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