Oxidation states of transition elements

For each of the oxidation states of the elements in the Oxidation States of Transition Elements activity (eChapter 20.3), identify the subshell(s) of the electrons being lost or shared. 

CO and related ligands stabilize very low oxidation states of transition elements, often zero (see below). 7i-acceptor interactions remove electron density from a metal atom and make possible a lower oxidation state than is commonly found with ligands such as water and ammonia. 

Equipment using high pressures with reactive gases has been developed mainly for fundamental scientific research. The stabilization of unusual oxidation states of transition elements is one area of research involving such equipment. Specific reaction vessels with external heating have been developed to synthesize oxides which require high temperatures (Fig. 7.11). Due to the large decrease of the mechanical properties of alloys with temperature, only a limited pressure-temperature domain is available (Fig. 7.12). 

A) Oxidation states of transition elements. In four large test tubes place about 20 ml of dilute solutions of titanic chloride, ammonium metavanadate, potassium dichromate, and ammonium molybdate. Add to each about 10 ml of concentrated hydrochloric acid and several grams of granulated or mossy zinc. Set under the draft. Note all the color changes and interpret them by means of ionic equations. 

The oxidation state of +8 for ruthenium and its mate osmium is the highest oxidation state of all elements in the transition series. Ruthenium s melting point is 2,310°C, its boiling point is 3,900°C, and its density is 12.45 glcvnr . 

The cyanide ion, CN, is isoelectronic with carbon monoxide and has an extensive chemistry of reaction with transition metals (e.g. the formation of the hexacyanoferrate(III) ion, [Fe(CN)63 ] by reaction with iron(III) in solution) but, unlike CO, it shows a preference for the positive oxidation states of the elements. This is mainly because of its negative charge. 

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

The insolubility of the hydroxides of the lower oxidation states of the transition elements is the reason for the general lack of aqueous chemistry in alkaline solutions. The higher oxidation states of the elements take part in covalency to produce oxoanions and persist even in alkaline conditions, and allow their solubility. 

Redox Reactions. Aquatic organisms may alter the particular oxidation state of some elements in natural waters during activity. One of the most significant reactions of this type is sulfate reduction to sulfide in anoxic waters. The sulfide formed from this reaction can initiate several chemical reactions that can radically change the types and amounts of elements in solution. The classical example of this reaction is the reduction of ferric iron by sulfide. The resultant ferrous iron and other transition metals may precipitate with additional sulfide formed from further biochemically reduced sulfate. Iron reduction is often accompanied by a release of precipitated or sorbed phosphate. Gardner and Lee (21) and Lee (36) have shown that Lake Mendota surface sediments contain up to 20,000 p.p.m. of ferrous iron and a few thousand p.p.m. of sulfide. The biochemical formation of sulfide is undoubtedly important in determining the oxidation state and amounts of several elements in natural waters. 

Cadmium is located at the end of the second row of transition elements. The +2 oxidation state of the element is the only one exhibited in its compounds. In its compounds, cadmium occurs as the Cd2+ ion. Cadmium is directly below zinc in the periodic table and behaves much like zinc. This may account in part for cadmium s toxicity because zinc is an essential trace element, cadmium substituting for zinc could cause metabolic processes to go wrong. 

Many of the transition elements exhibit more than one valence state, resulting from the possible removal of successive electrons from the inner partially filled d subshell. These d electrons may be removed singly or in groups thus the various oxidation states of an element may differ by one unit or hy more than one unit. As examples, the important oxidation states of vanadium are +3, +4, and +5 those for chromium are +2, + 3, and +6 and those for manganese are +2, +3, +4, +6, and +7. Among families of transition metals, the higher valence states become the more stable near the bottom of each family for example, in the chromium group the stability of the +6 states decreases in the order ... 

Ans. (a) Co + and Co + (the oxidation states of transition metals very in steps of one.) (b) TP and T1+ (the maximum oxidation state of a group III element and the state 2 less than the maximum.) (c) Sn" + and Sn + (the maximum oxidation state of a group IV element and the state 2 less than the maximum.) (d) Cu+ and Cu + (the maximum oxidation state for the coinage metals is greater than the group number.)... 

It is alloyed with about 4% A1 and 0.02% Mg. The aluminum strengthens the zinc and also prevents the molten alloy from attacking the steel pressure casting dies. Zinc readily reacts with mercury or will displace mercury from a mercury(II) salt to form an amalgam that is usefril for reductions, as in the preparation of compounds of the lower oxidation states of transition metals and lanthanides (e.g. Cr , V , Eu°, dimeric Mo ) and in analytical chemistry (e.g. in the Jones reductor see Analytical Chemistry of the Transition Elements). 

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-... 

Chemistry of the Various Oxidation States of Transition Metals 580 The Chemistry of Elements Potassium-Zinc Comparison by Electron Configuration 582... 

Having compared in general terms the properties of transition metals both on the basis of the d-electron configuration and the properties of the light versus heavier metals, we shall now look more specifically at the stabilities of the various oxidation states of each element in aqueous solution. Every oxidation state will not be examined in detail, but the emf data to make such an evaluation will be presented in the form of a Latimer diagram. 

Knowledge of the stable oxidation states of an element is very important since many other properties depend on these states. It is also important to know about the relative stability of oxidation states, i.e. redox potentials, for a chemical application. Trends in their values can also provide information about similarities or differences between the transactinides and their lighter homologues. Thus, for example, the stability of the maximum oxidation state is known to increase within transition element groups. It is therefore of great interest to investigate whether transactinides fall within this trend those at the beginning of the 6d row were expected to be stabilized in lower oxidation... 

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