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الموضوع: Oxidation States of the Transition Metals

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    عضو ذهبي الصورة الرمزية عزمي الزبن
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    افتراضي Oxidation States of the Transition Metals


    Oxidation States of the Transition Metals
    Most transition metals form more than one oxidation state.
    Some oxidation states, however, are more common than others. The most common oxidation states of the first series of transition metals are given in the table below. Efforts to explain the apparent pattern in this table ultimately fail for a combination of reasons. Some of these oxidation states are common because they are relatively stable. Others describe compounds that are not necessarily stable but which react slowly. Still others are common only from a historic perspective.
    Common Oxidation States of the First Series of Transition Metals
    Sc Ti V Cr Mn Fe Co Ni Cu Zn
    +1 d10
    +2 d3 d5 d6 d7 d8 d9 d10
    +3 d0 d3 d5 d6
    +4 d0 d3
    +5 d0
    +6 d0
    +7 d0



    One point about the oxidation states of transition metals deserves particular attention: Transition-metal ions with charges larger than +3 cannot exist in aqueous solution.
    Consider the following reaction in which manganese is oxidized from the +2 to the +7 oxidation state.
    Mn2+(aq) + 4 H2O(l) MnO4-(aq) + 8 H+(aq) + 5 e-



    When the manganese atom is oxidized, it becomes more electronegative. In the +7 oxidation state, this atom is electronegative enough to react with water to form a covalent oxide, MnO4-.
    It is useful to have a way of distinguishing between the charge on a transition-metal ion and the oxidation state of the transition metal. By convention, symbols such as Mn2+ refer to ions that carry a +2 charge. Symbols such as Mn(VII) are used to describe compounds in which manganese is in the +7 oxidation state.
    Mn(VII) is not the only example of an oxidation state powerful enough to decompose water. As soon as Mn2+ is oxidized to Mn(IV), it reacts with water to form MnO2. A similar phenomenon can be seen in the chemistry of both vanadium and chromium. Vanadium exists in aqueous solutions as the V2+ ion. But once it is oxidized to the +4 or +5 oxidation state, it reacts with water to form the VO2+ or VO2+ ion. The Cr3+ ion can be found in aqueous solution. But once this ion is oxidized to Cr(VI), it reacts with water to form the CrO42- and Cr2O72- ions.


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    افتراضي رد: Oxidation States of the Transition Metals

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    افتراضي رد: Oxidation States of the Transition Metals

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