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Variability of Relative Stability of Oxidation States.

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Introduction

Year: 2nd Date: 29th/04/03 Variability of Relative Stability of Oxidation States Generally speaking, there are several oxidation states for every element. However, why these elements are stable on their some particular oxidation states, how do they vary? The variability of relative stability of oxidation states is one of the most important ideas to study and understand. There are also some principles can state this topic. In addition, every group which is on the period table has the common ground on the oxidation states, and some especial examples. In other words, the element has the different stability if it is at different oxidation state. The variability of oxidation states for every element varies its stability and even its chemical property. Through the chemical period table, the relative oxidation states of each element can reflect the groups that they occupy. Thereby studying the variability of oxidation states is one of the best ways to analyze each group firstly. (1) Main group chemistry (the s-block elements) There are two groups on the s-block of the period table, those elements all are metals and have analogical chemical properties. +1 is the common oxidation state for group I, +2 is for the group II. Basically +1 and +2 are their most stable oxidation state for group I and group II respectively. The principal product of the reaction of the alkali metals with oxygen varies systematically down the group. ...read more.

Middle

In this case, four covalent bonds can be formed. Though the promotion of the s electron to the pz orbital requires some energy, this configuration is still desirable for the lighter, smaller elements of Group 14. This is because (as stated earlier, though in less detail) the energy required to promote the s electron to the pz orbital is negated by the release of energy from the additional two bonds that form. As for lead, it is more efficient to simply form two covalent bonds than it is to promote the s electron to the pz orbital in exchange for the energy released by the two extra covalent bonds. The reason that tin is stable in both the (II) and (IV) oxidation states is that the energy "costs" are similar in both situations for tin. In short, it requires similar "effort" on the part of the tin to both form two covalent bonds, or to promote an s electron and form four covalent bonds. (The oxidation states of tin, Mike ward, 1997, USA) Sn + 2I2 SnI4, Sn2+(aq) + 2I- SnI2(s) Nitrogen has one of the widest ranges of oxidation states of any element: compounds are known for each whole-number oxidation number from -3 (in NH3) to +5 (in nitric acid and the nitrates). It also occurs with fractional oxidation numbers, such as -1/3 in the azide ion, N3-. Usually the N2(gas) is the most stable (0 oxidation state). ...read more.

Conclusion

b is a constant which reflects the covalent radius of the element bonded to M in a binary compound, and is allocated a representative value of 1.0 A, although this can be varied in order to compare, e.g., fluorides with iodides. Stability index diagrams plot An against n. Examples given for elements of the 3d and 4f series, and for the Group 13 elements, demonstrate the value of such diagrams, and their construction helps students and teachers to rationalize the relative stabilities of oxidation states. (Smith, Derek W. Stability Index Diagrams: Pictorial Representations of the Relative Stabilities of Oxidation States for Metallic Elements J. Chem. Educ. 1996 73 1099.) Here is a new theory that Derek W. Smith developed. He found that the stability of oxidation state for metallic elements are apply to a energy equation: An = DeltaHof(Mn+, g) - an(n + 1)/(r + b). This equation is easier to see a metal element's stability. It made the microcosmic stability of oxidation state macroscopically. Conclusion The main factor is energy theory for the stability of a compound. But the relative oxidation states theory is a microcosmic factor. It is essential that the variability and relative stability of oxidation states is able to insight into a compound and their relative elements. Reference: 1. Chemical principles, Peter Atkins,2nd edition, 2000, Main groups. 2. Organometallic chemistry, A Unified Approach, R.C. Mehrotra, 1998. 3. Oxidation states of Tin, Mike ward, www.webelements.com. 4. Chemistry summarizing, Lan xinzhong, 2000, China Dalian. ...read more.

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