Elements of the first transition series

Helium had been named some years earlier when unknown spectral lines were observed in the spectrum of the sun. It had been suspected that the lines were caused by the presence of an unknown element. Ramsay now managed to isolate helium from a mineral called cleveite, and show that it had similar properties to argon. 

In 1898 Ramsay isolated three more gases in the group from liquid air - neon, krypton and xenon - all found to be chemically inert. The 

The block of elements between Group 2 and Group 13 of the Periodic T able are known as the transition eiements or d-biock eiements (Sc to Zn and the elements below them). The eiements of the first transition series are those elements that have partly filled d orbitals in any of their common oxidation states, which are the block of elements headed by Ti to Cu. Here, we will look mainly at the properties of the first transition series Ti, V, Cr, Mn, Fe, Co, Ni and Cu. These elements are typical metals and are often referred to as the transition metals. They have very similar physical properties. The changes in the atomic radii and first ionization energies across the first transition series are small, because each increase in nuclear charge is well shielded by the inner 3d electrons and only a small increased attraction is noticed by the outer electrons in the 4s subshell. See Box 12.7. 

The transition metals have the following properties in common  

They are hard and have high melting points, both indications that strong metallic bonding exists within the metals. 

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When the logarithm of k is plotted against metallic radius (Fig. 5) a correlation is observed for those elements with radii in the range 1.35-1.45 A. The correlation does not extend to those elements of the first transition series for which the radii are less than 1.30 A (with the exception of titanium, which obeys the correlation). This correlation lends some support to the view that there may be a critical intermediate in the exchange process the facile formation of which requires the matching of... 

Fortuitive experimental factors which make the catalytically important elements of the first transition series especially easy to study and... 

Fine structure spectra obtained at the X-ray X-absorption edge of an element are not yet completely resolved theoretically or experimentally. However it appears that this branch of spectroscopy even now may be of aid to catalyst research. Meaningful spectra of elements of the first transition series, even in concentrations sometimes as low as i%, can be readily obtained this is also true in conditions inaccessible by diffraction... 

This, the second volume of the series, covers the period October 1971 to September 1972 and follows the layout previously adopted in Volume 1 with only a few minor variations (see List of Contents). Thus Chapter 1 contains an account of the Chemistry of the Early Transition Metals excluding Scandium, Yttrium, and the Lanthanides. The Chemistry of the Elements of the first transition series Manganese to Copper is discussed in Chapter 2. Chapter 3 deals with the Noble Metals (Ru, Os, Rh, Ir, Pd, Pt, Ag, and Au) and Chapter 4 the Lanthanides (including Sc,Y, and La) and Actinides. 

In this section the redox properties of the 10 elements of the first transition series are discussed. The lower oxidation states ( + 2 and + 3, + l of Cu) of these elements are treated together and the higher states are described and discussed separately. 

The Lower Oxidation States of the Elements of the First Transition Series, Sc-Zn... 

As we go from left to right across the transition metals in the periodic table, the metal atoms become smaller, much as in the lanthanide contraction (Section 2.6). Furthermore, the atoms of elements of the first transition series are smaller than those of corresponding members of the second and third. Consequently, interstitial carbides are particularly important for metals toward the lower left of the series, as with TiC, ZrC, TaC, and the extremely hard tungsten carbide WC, which is used industrially as an abrasive or cutting material of almost diamond like hardness. The parallel with trends in chemisorption (Section 6.1) will be apparent. 

There is also an important difference displayed by heavier transition metals in their magnetic properties. Because of extensive spin-orbit coupling, the spin-only approximation (Chapter 11) is no longer valid. The simple interpretation of magnetic moment in terms of the number of unpaired electrons cannot be extended from the elements of the first transition series to their heavier congeners. 

The 18-electron rale is not obeyed as consistently by these types of oiganome-tank compounds a by the carbonyl and nitrosyl complexes and their derivatives. For example, in addition to ferrocene. M(i 5-CsHs)2 compounds are known for most of the other elements of the first transition series (M — V, Cr, Mn.Co, Ni) and these cannot obey ihe 18-electron rule. However, only ferrocene shows exceptional thermal stability (stable to 500 C) and is not oxidized by air. Furthermore, cobaltocene, a 19-electron species, is readily oxidized to the 18-electron cobaltocenium ion. (Co(ip-CsH )3)4 , which reflects much of the thermal stability of ferrocene. Mixed cyclopentadienyl carbonyl complexes are common K -CjHjMCO) ]. [(if-CjH )-Cr(CO), . [( -CjHOMnCCOjJ, [(>r-C,H,>Fe(CO ,, . [fo -CjiyCoCoy. and (ip-CsH,)Ni(CO) 2. Of interest is the fact that among these compounds, the odd-atomic-number elements (V. Mn, and Co) form monomers and the even-atomic-number elements (Cr. Fe. and Ni) Ibrm dimers, which is in direct contrast to the behavior shown by the simple carbonyl complexes. Cyclopentadienyl derivatives are now known for every main group and transition metal of the periodic table and for most of the -block metals.89... 

Crystal field theory is one of several chemical bonding models and one that is applicable solely to the transition metal and lanthanide elements. The theory, which utilizes thermodynamic data obtained from absorption bands in the visible and near-infrared regions of the electromagnetic spectrum, has met with widespread applications and successful interpretations of diverse physical and chemical properties of elements of the first transition series. These elements comprise scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel and copper. The position of the first transition series in the periodic table is shown in fig. 1.1. Transition elements constitute almost forty weight per cent, or eighteen atom per cent, of the Earth (Appendix 1) and occur in most minerals in the Crust, Mantle and Core. As a result, there are many aspects of transition metal geochemistry that are amenable to interpretation by crystal field theory. 

Figure 1.1 The periodic table. Elements of the first transition series are shown enclosed in the block.

The definition of a transition element, senso stricto, is that it is a metal having a partly filled d or/shell. A broader definition includes also those elements that have partially filled d or/shells in any one of their commonly occurring oxidation states. Elements of the first transition series have electronic configurations of the general form... 

Consider the elements of the first transition series in octahedral coordination. Ions with one, two or three 3d electrons (for example, Ti3+, V3+ and Cr3+, respectively) each can have only one electronic configuration, and the electrons occupy... 

Transition elements. Elements of the first transition series are characterized by having incompletely filled 3d orbitals in one or more of their common oxidation states. The series includes scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel and copper, which have electronic configurations of the form (ls)2(2s)2(2p)6(3s)2(3p)6(3[Pg.41]

Figure 8.6 Eh-pH diagrams for elements of the first transition series (from Brookins, 1990). The stability fields are calculated assuming that each dissolved transition metal has an activity of 10-6 (continued on facing page).

This relationship, which cannot be derived here, applies well if the unpaired electrons are situated on a nontransition metal atom or an element of the first transition series. It is inapplicable to the rare-earth and actinide ions in solution, for with these, the orbital angular momentum of the highly eccentric / electrons becomes comparable to their spin moment. 

Elements of the first transition series from vanadium to nickel form stable bis(7j-cyclopentadienyl) complexes having the normal ir-sandwich structure typical of ferrocene. In contrast, bis(Tj-cyclopentadienyl)ti-tanium, (i7-CsH5)2Ti (1), is not even known as a discrete compound. 

We discuss in this chapter the elements of the first transition series, titanium through copper. There are two main reasons for considering these elements apart from their heavier congeners of the second and third transition series (1) in each group (e.g., V, Nb, and Ta) the first-series element always differs appreciably from the heavier elements, and comparisons are of limited use, and (2) the aqueous chemistry of the first-series elements is much simpler, and the use of ligand field theory in explaining both the spectra and magnetic properties of compounds has been far more extensive. 

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