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The d-and f-Block Elements — Chemistry STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceChemistryThe d-and f-Block Elements3 Marks
Question
Write a note on halide compounds of Transition elements.
✓

Answer

$\rightarrow$ The Transition elements form Ionic halides with fluorine and co$-$valent halides with chlorine, bromine and iodine.
$\rightarrow$ The highest oxidation numbers are achieved in $TiX _4 ($tetrahalides$), VF_5$ and $CrF_{6.}$
$\rightarrow$ Mn is not known in $+7$ oxidation state with fluorine i.e. $MnF$, is not known. But $MnO_3F$ is known because oxygen stabilizes the compound due to its tendency to form a multiple bonds.
$\rightarrow$ The ability of fluorine to stabilise the highest oxidation state is due to either higher lattice energy as in the case of $CoF_3,$ or higher bond enthalpy terms for the higher covalent compounds, e.g., $VF_5$ and $CrF_6$
$\rightarrow$ Although $V ^{ V }$ is represented only by $VF _5,$ the other halides, however, undergo hydrolysis to give oxohalides, $VOX _3.$ Another feature of fluorides
$\ce{VF _5+ H _2 O \rightarrow VOF _3+2 HF}$
$\rightarrow$ The solution of metal halides are acidic as they produce acid on hydrolysis.
$\rightarrow$ All halides of copper such as $\ce{CuF _2, CuCl _2}$ and $CuBr _2$ are known. However $CuI _2$ is not know because $Cu ^{2+}$ is good oxidising agent while $1$ is good reducing agent. So they form $Cu _2 I _2$ on reaction with each other.
$\ce{2 Cu ^{2+}+4 I ^{-} \rightarrow Cu _2 I _{2(s)}+ I _2}$
$\rightarrow$ However, many copper $(I)$ compounds are unstable in aqueous solution and undergo disproportionation.
$\ce{2 Cu ^{+} \rightarrow Cu ^{2+}+ Cu}$
$\rightarrow$ The stability of $\ce{Cu ^{2+} (aq)}$ rather than $\ce{Cu ^{+}(aq)}$ is due to the much more negative $\ce{\Delta_{\text {hyd }} H ^{\ominus} of Cu ^{2+} (aq)}$ than $\ce{Cu ^{+},}$ which more than compensates for the second ionization enthalpy of $Cu .$
Formulas of Halides of $3d$ Metals
Oxidation Number                  
$+6$     $CrF_6$            
$+5$   $VF_5$ $CrF_5$            
$+4$ $TiX_4$ $VX_4^1$ $CrX_4$ $MnF_4$          
$+3$ $TiX_3$ $VX _3$ $CrX_3$ $MnF_3$ $FeX_3^1$ $CoF_3$   $CuX _2{ }^{11}$ $ZnX _2$
$+2$ $TiX _2{ }^{ III }$ $VX _2$ $CrX_2$ $MnF_2$ $FeX _2$ $CoX _2$ $NiX _2$ $CuX ^{111}$  
$+1$                  
K e $\ce{y: X=F \rightarrow I ; X^1=F \rightarrow B r ; X^{11}=F, C l ; X^{111}=C l \rightarrow I}$

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