Transition metal ions electron configuration

Moreover, the analysis of the optical spectra of transition metal and rare earth ions is very illnstrative, as they present qnite different features due to their particular electronic configurations transition metal ions have optically active unfilled outer 3d shells, while rare earth ions have unfilled optically active 4f electrons screened by outer electroiuc filled shells. Because of these unfilled shells, both kind of ion are usually called paramagnetic ions. 

Transition metal ions have an incompletely filled d-shell, i.e. their electron configuration is d". The optically active electrons are thus bound to central potential as well as experiencing crystal field potential, and are not shielded by outer electrons. Most transition metal ions are multi-valent. Mainly the number of 3d electrons and the crystal field determine their optical properties. Thus the groups below have similar optical behavior ... 

In general, octahedral complexes of transition-metal ions possessing 0, 1, or 2 electrons beyond the electronic configuration of the preceding noble gas, ie, i/, (P configurations, are labile. The (P systems are usually inert the relative lability of vanadium(II) may be charge and/or redox related. 

Table 1-2. The electronic configurations of the transition-metal ions in the divalent and triva-lent states.

Unpaired electrons and magnetism - One of the consequences of the open (incompletely filled) d" configuration of transition-metal ions may be the presence of one or more unpaired electrons. Such compounds could be described as radicals, and they are detected by techniques such as electron spin resonance spectroscopy. 

Fig. 4.20 A schematic view of the ground state terms of a transition metal ion with 3d electron configuration and spin S = 5/2, such as in high-spin iron(III), under various perturbations with decreasing interaction strength from left to right...

Being able to write correct electron configurations for transition metal ions becomes very important in discussions of coordination compounds (Chemistry 2). 

The lanthanides have electrons in partly filled 4/orbitals. Many lanthanides show colors due to electron transitions involving the 4/orbitals. However, there is a considerable difference between the lanthanides and the 3d transition-metal ions. The 4/ electrons in the lanthanides are well shielded beneath an outer electron configuration, (5.v2 5p6 6s2) and are little influenced by the crystal surroundings. Hence the important optical and magnetic properties attributed to the 4/ electrons on any particular lanthanide ion are rather unvarying and do not depend significantly upon the host structure. Moreover, the energy levels are sharper than those of transition-metal ions and the spectra resemble those of free ions. 

Not all bare metal ions are highly reactive Cr+ and Mn+ are the two first-row transition metal ions that have low reactivity. The electronic configuration of the ion must be important in reactivity but may not be the only property of the ion that influences reactivity, shown by the reactions of these bare ions with S8 and P4 in comparison with other transition and non-transition metal ions. 

The Cr+ and Mn+ ions have ground-state electronic configurations 3<754.v° and 3d54s1, respectively, and both react slowly (relative to other transition metal ions) with S8 but do not react with P4 (whereas other transition metal ions react readily). The Ca+ (3d°4s1) ion reacts rapidly with S8 (98) (more rapidly than most bare transition metal ions) but reacts very slowly with P4 producing the [CaP]+ ion. The Ba+ ion also reacts readily with S8 but is unreactive to P4 (99). These observations indicate that the electronic configuration of the metal ion and the properties of the reacting molecule are important in determining reactivity. The formation of stable product ions is also important. Whereas most transition metals react with S8 to produce [MS4]+ ions, the product ion for Ca+ and Ba+ is the [MS3]+ ion. 

Most stable ground-state molecules contain closed-shell electron configurations with a completely filled valence shell in which all molecular orbitals are doubly occupied or empty. Radicals, on the other hand, have an odd number of electrons and are therefore paramagnetic species. Electron paramagnetic resonance (EPR), sometimes called electron spin resonance (ESR), is a spectroscopic technique used to study species with one or more unpaired electrons, such as those found in free radicals, triplets (in the solid phase) and some inorganic complexes of transition-metal ions. 

Chapter 6 is devoted to discussing the main optical properties of transition metal ions (3d" outer electronic configuration), trivalent rare earth ions (4f 5s 5p outer electronic configuration), and color centers, based on the concepts introduced in Chapter 5. These are the usual centers in solid state lasers and in various phosphors. In addition, these centers are very interesting from a didactic viewpoint. We introduce the Tanabe-Sugano and Dieke diagrams and their application to the interpretation of the main spectral features of transition metal ion and trivalent rare earth ion spectra, respectively. Color centers are also introduced in this chapter, special attention being devoted to the spectra of the simplest F centers in alkali halides. 

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