Transition elements, common oxidation states

Except for the elements at the ends of the rows, each transition metal can exist in several different oxidation states. The oxidation states displayed by the 3d transition metals are shown in Table 20-1. The most important oxidation states are highlighted in the table. The most common oxidation state for the 3d transition metals is +2, known for all the elements except Sc. Chromium, iron, and cobalt are also stable in the +3 oxidation state, and for vanadium and manganese the -H4 oxidation state is stable. Elements from scandium to manganese have a particularly stable oxidation state corresponding to the loss of ah the valence electrons configuration). 

Symbol Ni atomic number 28 atomic weight 58.693 a transition metal element in the first triad of Group VIll(Group 10) after iron and cobalt electron configuration [Ar]3d 4s2 valence states 0, -i-l, +2, and -f-3 most common oxidation state +2 the standard electrode potential, NF+ -1- 2e Ni -0.237 V atomic radius 1.24A ionic radius (NF+) 0.70A five natural isotopes Ni-58 (68.08%), Ni-60 (26.22%), Ni-61 (1.14%), Ni-62 (3.63%), Ni-64 (0.93%) nineteen radioactive isotopes are known in the mass range 51-57, 59, 63, 65-74 the longest-lived radioisotope Ni-59 has a half-life 7.6x10 years. 

Titanium is the first member of the 3d transition series and has four valence electrons, 3d24s2. The most stable and most common oxidation state, +4, involves the loss of all these electrons. However, the element may also exist in a range of lower oxidation states, most importantly as Ti(III), (II), (0) and —(I), Zirconium shows a similar range of oxidation states, but the tervalent state is much less stable relative to the quadrivalent state than is the case with titanium. The chemistry of hafnium closely resembles that of zirconium in fact, the two elements are amongst the most difficult to separate in the periodic table. 

In contrast to the lanthanide 4f transition series, for which the normal oxidation state is +3 in aqueous solution and in solid compounds, the actinide elements up to, and including, americium exhibit oxidation states from +3 to +7 (Table 1), although the common oxidation state of americium and the following elements is +3, as in the lanthanides, apart from nobelium (Z = 102), for which the +2 state appears to be very stable with respect to oxidation in aqueous solution, presumably because of a high ionization potential for the 5/14 No2+ ion. Discussions of the thermodynamic factors responsible for the stability of the tripositive actinide ions with respect to oxidation or reduction are available.1,2... 

In common with other nitrogen donor ligands, the majority of reported coordination compounds are with later d transition elements, or early B subgroup elements, in oxidation states of II or III. Tetraaza macrocycles predominate, with 14 followed by 16 as the most common ring sizes. 

FIGURE 20.6 Common oxidation states for first-series transition elements. The states encountered most frequently are shown in red. The highest oxidation state for the group 3B-7B metals is their periodic group number, but the group 8B transition metals have a maximum oxidation state less than their group number. Most transition elements have more than one common oxidation state. 

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]

The transition metals can form a variety of ions by losing one or more electrons. The common oxidation states of these elements are shown in Table 20.2. Note that for the first five metals the maximum possible oxidation state corresponds to the loss of all the 4s and 3d electrons. For example, the max-... 

FIGURE 8.4 Some of the oxidation states found in compounds of the transition-metal elements. The more common oxidation states are represented by solid circles, and the less common ones are represented by open circles. 

The f block elements Lanthanide and actinide elements. These two series often appear with a or in Group IIIB (3), but these elements do not belong to that family. (Note that the transition metals do not belong to group IIA (2), which they follow.) The most common oxidation state for the lanthanides and some of the actinides is +3, hence the popularity of the IIIB (3) position. Because of their remarkable electronic and chemical properties they should be set apart, but most periodic tables give no special numerical appellations to these elements. 

The most common oxidation states of the 32/-transition elements are +2 and + 3. The elements in the middle of each series exhibit more oxidation states than those to the left or right. As one moves down a group, higher oxidation states become more stable and more common (opposite to the trend for representative elements). This is because the d electrons are more effectively shielded from the nucleus as the group is descended and are therefore more easily lost or more readily available for sharing. For example, cobalt commonly exhibits the +2 and +3 oxidation states. Rh and Ir are just below Co. Their common oxidation states are +3 and +4. The +4 state is slightly more stable for Ir than for the lighter Rh. 

Titanium is the first member of the block transition elements and has four valence electrons, 3d2As2. Titanium(iv) is the most stable and common oxidation state compounds in lower oxidation states, —I, 0, II and III, are quite readily oxidized to Tilv by air, water or other reagents. The energy for removal of four electrons is high, so that the Ti4+ ion does not have a real... 

The element belongs to the large group of transition elements or d block. The position within the Periodic Table of the elements is below zinc and above mercury. The zinc group has a filled d ° orbital and is transitional between the d block and the p block elements of boron and others. The outer electronic configuration of the zinc group is d S and the common oxidation state is -i- II. 

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. 

As noted in Chapter 4, the transition metals exhibit variable oxidation states in their compounds. Figure 20.3 shows the oxidation states from seandium to copper. Note that the common oxidation states for each element inclnde +2, +3, or both. The +3 oxidation states are more stable at the beginning of the series, whereas toward the end, the +2 oxidation states are more stable. The reason is... 

Multiple Oxidation States One of the most characteristic chemical properties of the transition metals is the occurrence of multiple oxidation states main-group metals, display one or, at most, two states. For example, vanadium has two common oxidation states, chromium and manganese have three (Figure 22.5A), and many others are seen less often (Table 22.2). Since the ns and (n — l)d electrons are so close in energy, transition elements can use all or most of these electrons in bonding. 

Sometimes, too, chemists include the two rows of elements at the bottom of the periodic table with the transition elements. These two rows, often referred to as the inner-transition elements, have partially filled/subshells in common oxidation states. The elements in the first row are called the lanthanides, or rare earths, and the elements in the second row are called the actinides. Figure 23.1 shows the divisions of the transition elements. The B columns of transition elements, as well as the inner-transition elements, frequently form complex ions and coordination compounds. 

Initiator a compound that produces free radicals in a reaction for the preparation of an addition polymer. (25.1) Inner-transition elements the two rows of elements at the bottom of the periodic table (2.5) the elements with a partially fllled/subshell in common oxidation states. (8.2 and p. 959)... 

---