Oxidation number periodic variation

In compounds, metals are cations. That is, they will have a positive charge. The cations may be shown with the corresponding anions in solution, or in some particular problems, only the metal cation may be shown. In both of these cases, you may see designations such as Al3+. The metals contained in the leftmost two columns on the periodic table always form +1 and +2 ions, respectively. All other columns contain metals that may adopt more than one oxidation state. Variations in oxidation numbers are prevalent amongst the transition metals. No oxidation number ever exceeds the number at the top of the column on the periodic table. The highest oxidation number known for any metal in a compound is +8. 

Fig. 14 Variation of the coordination number Vc(M-O) of selected metals in their maximum oxidation state in oxides (a, b) variation of Nq with the group numlxu- along selected rows of the periodic table, (c) with the row number for alkali and alkaline earth catirais. (d) Variation of Nc in lanthanide cations with the atomic number...

The redox behaviour of Th, Pa and U is of the kind expected for d-transition elements which is why, prior to the 1940s, these elements were commonly placed respectively in groups 4, 5 and 6 of the periodic table. Behaviour obviously like that of the lanthanides is not evident until the second half of the series. However, even the early actinides resemble the lanthanides in showing close similarities with each other and gradual variations in properties, providing comparisons are restricted to those properties which do not entail a change in oxidation state. The smooth variation with atomic number found for stability constants, for instance, is like that of the lanthanides rather than the d-transition elements, as is the smooth variation in ionic radii noted in Fig. 31.4. This last factor is responsible for the close similarity in the structures of many actinide and lanthanide compounds especially noticeable in the 4-3 oxidation state for which... 

Mendeleev was bolder in his interpretation than Lothar Meyer, and for this reason we honor him as the primary discoverer of the modem periodic table. A few elements did not fit the pattern of variation in combining numbers with molar mass. Mendeleev proposed that these irregularities meant that the element s molar mass had been measured incorrectly. For example, Mendeleev predicted that the correct molar mass of indium is 113 g /mol, not 75 g /mol, the value assigned at that time on the assumption that the formula for indium oxide is InO. Later experiments showed that the correct formula is L12 O3, and indium s tme molar mass is 114.8 g/mol. 

As indicated by the values in Table 7.2.1, the periodate oxidation method yields consistently higher values (8 and 10% for Norway spruce and aspen wood meals, respectively) for phenolic hydroxyl content than are obtained using the aminolysis procedure. The reasons for these variations are not clear. However, in a series of replicate determinations, the aminolysis method has a considerably higher standard deviation compared to the periodate method which may be partly attributable to the larger number of steps involved in the analysis. 

Metal-cluster skeletons are defined by the number of metal cluster electrons (MCE) this in turn is determined by the positions of the metallic elements in the periodic table, and by their oxidation states. A general principle is the availability of vacant metal coordination sites for the formation of metal-metal bonds and of the valence eleetrons to be used in the formation of these bonds. Metals in relatively low oxidation states are, therefore, favored and the value of MCE corresponds to the number of M M bonds if electron-precise 2c 2e bonding is assumed. Several empirical rules have been established which describe the relationships between MCE and cluster shape. " There is some variation in the modes by which the clusters are linked, depending on the oxidation states of the component metals and on the number of vacant coordination sites on metals. 

Table 5.2 shows the variations of valency, i.e. the number of single electron-pair bonds, of the elements of the s- and p-blocks. The oxidation states (Roman numerals) of the metallic elements are indicated instead of their valency. The elements of the 2nd period, Li to Ne, show the values expected from the strict application of the octet rule. The elements of the subsequent periods follow the rule, but there are many exceptions... 

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