D block

Elements in the s and p blocks of the table are referred to as typical elements whilst those in the d block are called transition elements and those in the/block are called actinides and lanthanides (or rare earth elements). 

There is a lively controversy concerning the interpretation of these and other properties, and cogent arguments have been advanced both for the presence of hydride ions H" and for the presence of protons H+ in the d-block and f-block hydride phases.These difficulties emphasize again the problems attending any classification based on presumed bond type, and a phenomenological approach which describes the observed properties is a sounder initial basis for discussion. Thus the predominantly ionic nature of a phase cannot safely be inferred either from crystal structure or from calculated lattice energies since many metallic alloys adopt the NaCl-type or CsCl-type structures (e.g. LaBi, )S-brass) and enthalpy calculations are notoriously insensitive to bond type. 

Attempts to classify carbides according to structure or bond type meet the same difficulties as were encountered with hydrides (p. 64) and borides (p. 145) and for the same reasons. The general trends in properties of the three groups of compounds are, however, broadly similar, being most polar (ionic) for the electropositive metals, most covalent (molecular) for the electronegative non-metals and somewhat complex (interstitial) for the elements in the centre of the d block. There are also several elements with poorly characterized, unstable, or non-existent carbides, namely the later transition elements (Groups 11 and 12), the platinum metals, and the post transition-metal elements in Group 13. 

The occurrence of slMc neutral bipaiy caiboi ls IS restricted to the centra) area of the d block 1 -3). wbere there are low-... 

The binary borides (p. 145), carbides (p. 299), and nitrides (p. 418) have already been discussed. Suffice it to note here that the chromium atom is too small to allow the ready insertion of carbon into its lattice, and its carbide is consequently more reactive than those of its predecessors. As for the hydrides, only CrH is known which is consistent with the general trend in this part of the periodic table that hydrides become less stable across the d block and down each group. 

Iron is notable for the range of electronic spin states to which it gives rise. The values of S which are found include every integral and half-integral value from 0 to i.e. every value possible for a d-block element (Table 25.4). 

A contraction resulting from the filling of the 4f electron shell is of course not exceptional. Similar contractions occur in each row of the periodic table and, in the d block for instance, the ionic radii decrease by 20.5 pm from Sc to Cu , and by 15 pm from Y to Ag . The importance of the lanthanide contraction arises from its consequences ... 

The Natural Atomic Orbitals for atom A in the molecular environment may be defined as those which diagonalize the block, NAOs for atom B as those which diagonalize the D block etc. These NAOs will in general not be orthogonal, and the orbital oecupation numbers will therefore not sum to the total number of electrons. To achieve a well-defined division of the electrons, the orbitals should be orthogonalized. 

FIGURE 4. Medium-long form table showing highest and most common oxidation states of the d-block elements. Only two of these 30 ions, Ag+1 and Au+3, (shown in bold-face) show anomalous electronic configurations with respect to other ions in the same groups. 

Green MLH, Green JC (In preparation) Systematic chemistry of covalent compounds of the d-block transition metals Seddon EA, Seddon KR (1984) The chemistry of ruthenium, Elsevier, Amsterdam... 

FIGURE 1.38 The seven /-orbitals of a shell (with n = 3) have a very complex appearance. Their detailed form will not be used again in this text. However, their existence is important for understanding the periodic table, the presence of the lanthanoids and actinoids, and the properties of the later d-block elements. A darker color denotes a positive lobe, a lighter color a negative lobe. 

The low ionization energies of elements at the lower left of the periodic table account for their metallic character. A block of metal consists of a collection of cations of the element surrounded by a sea of valence electrons that the atoms have lost (Fig. 1.53). Only elements with low ionization energies—the members of the s block, the d block, the f block, and the lower left of the p block—can form metallic solids, because only they can lose electrons easily. 

All d-block elements are metals (Fig. 1.63). Their properties are transitional between the s- and the p-block elements, which (with the exception of the members of Group 12) accounts for their alternative name, the transition metals. Because transition metals in the same period differ mainly in the number of /-electrons, and these electrons are in inner shells, their properties are very similar. 

FIGURE 1.63 The elements in the first row of the d block. Top row magnet is levitated by the superconductor If the assembly were (left to right) scandium, titanium, vanadium, chromium, and turned over, the magnet would hang at about the same distance... 

All d-block elements are metals with properties between those ofs-block and p-block metals. Many d-block elements form cations in more than one oxidation state. 

In the d block, the energies of the (n — l )d-orbitals lie below those of the ns-orbitals. Therefore, the ws-electrons are lost first, followed by a variable number of (n — 1 )d-electrons. For example, to obtain the configuration of the Fe3+ ion, we start from the configuration of the Fe atom, which is [Ar]3d 64s2, and remove three electrons from it. The first two electrons removed are 4s-electrons. The third electron comes from the Id-subshell, giving [Ar 3d5. 

Many metallic elements in the p and d blocks, have atoms that can lose a variable number of electrons. As we saw in Section 1.19, the inert-pair effect implies that the elements listed in Fig. 1.57 can lose either their valence p-electrons alone or all their valence p- and s-electrons. These elements and the d-block metals can form different compounds, such as tin(II) oxide, SnO, and tin(IV) oxide, Sn02, for tin. The ability of an element to form ions with different charges is called variable valence. 

Because the metallic radii of the d-block elements are all similar, they can form an extensive range of alloys with one another with little distortion of the original crystal structure. An example is the copper-zinc alloy used for some copper coins. Because zinc atoms are nearly the same size as copper atoms and have simi-... 

The product of the second reaction is sodium aluminate, which contains the alumi-nate ion, Al(OH)4. Other main-group elements that form amphoteric oxides are shown in Fig. 10.7. The acidic, amphoteric, or basic character of the oxides of the d-block metals depends on their oxidation state (Fig. 10.8 also see Chapter 16). 

Metals form basic oxides, nonmetals form acidic oxides the elements on a diagonal line from beryllium to polonium and several d-block metals form amphoteric oxides. 

---