Iron triad elements

Describe the electron configurations for the Iron triad elements In their most common oxidation states. 

The reactions of the iron triad elements are many and varied. The metals are more active than hydrogen and liberate H2(g) from an acidic solution. Hydrated Co and Ni are red and green, respectively. In aqueous solution, Fe " " is pale green and fully hydrated Fe is purple. (Generally, however, solutions of Fe " "(aq) are yellow to brown, but this color probably results from the presence of species formed in the hydrolysis of Fe (aq). Like the hydrolysis of Al " "(aq), described on page 777, that of Fe (aq) produces an acidic solution. 

The iron triad elements (Fe, Co, and Ni) exhibit a variability in oxidation state with +2 the most common. Like other transition elements these metals form compounds with carbon monoxide called metal carbonyls. 

Called the Iron Triad on the periodic chart, the elements are ... 

Molybdenum is in the middle of the triad elements of group 6. These three metals (from periods 4, 5, and 6) are chromium, molybdenum, and tungsten, which, in their pure states, are relatively hard, but not as hard as iron. They are silvery-white as pure metals, and they have similar oxidation states. Their electronegativity is also similar—Cr = 1.6, Mo = 1.8, and W = 1.7—which is related to their reactivity with nonmetals. 

The nearly identical atomic radii of the iron triad—iron, cobalt, and nickel —help explain the similar chemistry of these three elements. The similarities among the platinum group elements in Periods 5 and 6 emphasize the fact that there is little difference between the atomic radii of the elements in these periods in which inner d orbitals are being filled. The coinage metals show the expected similarity among elements in the same group. 

Among the iron triad metals most complexes are iron Tc-allyl adducts from dienes. This may be fortuitous or owing to an electronic property of the heavier elements. The ruthenium diene complex XXIXa shows no tendency to undergo insertion s, but the origin of this may be steric, as indicated by the protonation of (CO)3Ru(butadiene), which goes via complex XXIXb and yields XXXa S ... 

The elements Fe, Co and Ni, the triad in the middle of the periodic table, are similar from the chemical point of view but quite different in their influence on the environment and their significance for life. As described in Chapter 8 Iron, this element is tremendously important for human Hfe, as its atom is essential in hemoglobin and is thus responsible for oxygen uptake in the lungs. Cobalt, present in the form of vitamin Bj2, is necessary to prevent serious anemia. The role of nickel in mammals and humans is very Hmited and confined to its presence in one single enzyme, urease, which catalyzes the decomposition of urea to ammonia. Nickel was, however, very important in a very early epoch of life on earth. 

Iron, cobalt, and nickel are similar in properties and are sometimes studied together as the iron triad. For example, each is a fairly active metal that reacts with acids to give hydrogen and the -1-2 ions. In addition to the -1-2 ions, the -1-3 ions of the metals also figure prominently in the chemistries of the elements. Explain why these elements are similar. 

Periodic table. Locate the following classes of elements on Table 7.4, page 109 (a) the alkali metals, (b) the halogens, (c) the noble gases, (d) the alkaline earth metals, (e) the iron triad, (f) the rare earth elements, (g) the coinage metals. 

Most of the transition elements do not react with strong acids, such as HCl and H2SO4. Some do have negative standard reduction potentials for the reaction M"+ -I- ne - M, and liberate hydrogen from hydrochloric acid. These include Mn, Cr, and the iron triad. Silver, gold, the palladium triad, and the platinum triad, the so-called noble metals, are especially inert to acids, both to the nonoxidizing species, such as hydrochloric and hydrofluoric acids, and to the oxidizing acids, such as nitric acid. 

Osmium is the least studied element of the iron triad and its main use consists in the preparation of stable models for reactive intermediates involved in reactions catalysed by ruthenium analogues. Although NHC-Os compounds were first synthesised by Lappert in the late 19708, " their catalytic properties were investigated only very recently. 

Kuz ma et al. (1986a) and Lomnitskaya and Kuz ma (1991a) showed that phosphorus behaves as a metallic element in ternary M-M -P systems at low P content (up to 25 at.%), as indicated by the formation of phosphorus solid solutions in binary intermetallic compounds (e.g., Zr2pe, Zr2Co). In ternary compounds phosphorus atoms occupy the same positions as iron triad metals in the structure. At phosphorus contents up to 33.3 at.%, metallic-type chemical bonds occur in the compounds, and there are no P-P contacts. 

Kuz ma, Yu.B., Ya.F. Lomnitskaya and S.V. Oryshchyn, 1986a, The interaction of phosphorus with transition metals of IVa-Vla group elements and iron triad metals, in Stable and Metastable Phase Equilibria in Metallic Systems, ed. M.E. Drits (Nauka, Moscow) p. 12-18. In Russian. 

General Properties 23-2 Principles of Extractive Metallurgy 23-3 Metallurgy of Iron and Steel 23-4 First-Row Transition Elements Scandium to Manganese 23-5 The Iron Triad Iron, Cobalt, and Nickel... 

The transition elements iron, cobalt, and nickel comprise the iron triad. Iron, with an annual worldwide production of more than 1.1 billion metric tons, is the most important metal in modern civilization. It is widely distributed in Earth s crust at an abundance of 4.7%. The major commercial use of iron is to make steel (see Section 23-3). 

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. 

Although iron, cobalt, and nickel occur in the same triad in Group VIII., the three elements differ considerably in their ability to form addition compounds with ammonia. Iron forms few ammino-salts, most of which are unstable, and its tendency to complex-salt formation of the ammine type appears in the complex cyanides and not in the ammines themselves. 

Cobalt. The speciation of radiocobalt has been selected for discussion in this chapter because it exemplifies an element for which much information already exists regarding its stable chemical speciation, yet there are additional species which have become environmentally important as a result of the activities of the nuclear industry Cobalt, the middle member of the first triad of group VIII transition metals in the Periodic Table (iron, cobalt, nickel), is most stable in the divalent state when in simple compounds. Studies of radionuclide releases from nuclear power plants under tropical conditions in India seem to indicate that... 

We place hydrogen as the first element in the first period, along with helium. When helium was discovered, Mendeleev put it in the second period. We put the triads of iron, cobalt, and nickel ruthenium, rhodium and palladium and osmium, iridium, and platinum in group VIIIB, in the middle of the table. Mendeleev put them in group VIII. We also have two long groups, the lanthanides and actinides, that were a headache for Mendeleev. 

In Group VIII, each position instead of being filled by a single element is occupied by a group of three elements. Thus there appear in triads iron, cobalt, and nickel ruthenium, rhodium, and palladium and osmium, iridium, and platinum. In this group there is no subdivision into families, but all the members are heavy metals. 

Not only do the elements in each of the above triadic groups exhibit a more or less regular gradation in their properties, but. a certain amount of similarity is found to exist between a member of any one triad and the corresponding members of the other triads. Thus, for example, iron, ruthenium, and osmium have several interesting peculiarities in common so have cobalt, rhodium, and iridium, as well as nickel, palladium, and platinum. 

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