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    Generality of transition elements

    • Last Update: 2021-06-30
    • Source: Internet
    • Author: User
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    1.
    The physical properties of the element

    Transition metals have metallic luster, good ductility, electrical conductivity and thermal conductivity
    .


    A variety of alloys can be formed between transition metals


    In addition to s electrons participating in the formation of metal bonds in transition metals, d electrons also participate in the formation of bonds, so the melting point and boiling point are relatively high
    .


    In the third transition series metals, the melting points of tantalum, tungsten, rhenium, and hungry are all above 3000°C


    Table 16-1 Melting point and density of some transition metals

    The density of transition metals is high
    .


    Among them, the density of rhenium, iridium, iridium, and platinum exceeds 20g·cm -3 , and Russia is the most dense element


    Except for the abnormal melting point of lanthanum of group IIIB, the elemental elements of the transition elements of other groups (columns) increase in melting point and density from top to bottom
    .


    For the transition metals in the same period, the melting point changes basically gradually increase first, the VIB elements reach the highest, and then gradually decrease, which is consistent with the change law of the metal single electron number; the density change basically increases gradually in the same period


    High hardness transition metals, such as chromium , manganese , molybdenum , ruthenium , tungsten , tantalum , rhenium , hungry Mohs hardness are more than
    6 .


    Among them, metallic chromium has the highest hardness with a hardness of 9, which is second only to the hardness of diamond in the simple substance


    2 oxidation state

    Because d electrons in transition elements participate in the formation of chemical bonds, they often exhibit multiple oxidation states in their compounds.


    The highest oxidation state ranges from +3 of group IIIB elements ( scandium , yttrium , lanthanum ) to group VIII elements (ruthenium, lanthanum ).


    In the same family, the high oxidation state tends to be stable as the number of cycles increases
    .


    For example, the stable oxidation state of chromium is +3, and the oxidation state of +6 is unstable; while the stable oxidation state of molybdenum and tungsten is +6; in the column of iron, ruthenium, and hungry, the highest oxidation state of iron is +6, while the highest oxidation state of iron is +6.


    In the fourth period elements, from Sc to Mn, 3d and 4s electrons are easy to participate in bonding, and the highest oxidation state with the same group number is relatively stable: Sc, +3; Ti, +4; V, +5; Cr, +6; Mn, +7
    .


    From Fe to Ni, the stability of high oxidation states is reduced: Fe, +2 and +3; Co, +2; Ni, +2; trivalent cobalt and nickel have strong oxidizing properties and are extremely unstable


    3 Colors of compounds and ions

    Transition metal compounds, hydrate ions and complex ions generally have colors.
    The cause of the color development can be attributed to the dd transition of the metal and the charge transfer between positive and negative ions
    .

    The d orbitals of transition metals generally have electrons and are not full.
    The electrons absorb visible light and undergo dd transitions to show their complementary colors, such as [V(H 2 O) 6 ] 2+ , purple; [Cr(H 2 O) 6 ] 2 + , Blue; [Cr(H 2 O) 6 ] 3+ , purple; [Mn(H 2 O) 6 ] 2+ , light red; [Fe(H 2 O) 6 ] 2+ , green; [Co (H 2 O) 6 ] 2+ , pink; [Ni(H 2 O) 6 ] 2+ , green
    .

    The dd transition may also be accompanied by charge migration
    .
    Both Mn 2+ and Fe 3+ have 5 d electrons, but the Mn 2+ compound has a lighter color, while the Fe 3+ compound has a darker color
    .
    For example, Mn(OH) 2 is white, MnS·H 2 O is pink, Fe(OH) 3 is brown, and Fe 2 S 3 is black.
    The reason is that Fe 3+ has strong polarization ability and charge transfer with negative ions
    .

    Certain transition metals having D 0 electronic configuration or a compound containing oxygen acid ions may also have a color, the causes of the occurrence of charge transport, such as the yellow of CrO .
    4
    2- , Purple of MnO .
    4
    - , yellow NBCI .
    5
    and the like
    .

    4 coordination compound

    Transition elements have empty d orbitals that can accept electron-pair coordination bonds and a high charge/radius ratio, so it is easy to form stable coordination compounds
    .
    The formation of transition metal complexes is of great significance.
    For example, the formation of [Zn(CN) 4 ] 2- ions is widely used in the recovery of gold in low-grade gold mines; vitamin Be (coordination compound of cobalt), heme (Coordination compounds of iron), etc.
    , play a very important role in the process of life; some complexes of transition elements are often used as catalysts or as intermediates in catalytic reactions
    .

    Related links: Interconversion of Hg(I) and Hg(IⅡ)

     

     

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