Transition and InnerTransition Elements - Result Question 86

####13. The transition element having least enthalpy of atomisation is

(2019 Main, 9 Jan II)

(a) $Zn$

(b) $V$

(c) $Fe$

(d) $Cu$

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Solution:

  1. For transition metals,

$\Delta H _{\text {Atomisation }}^{\circ} \propto$ Strength of metallic bonding

$\propto$ Number of unpaired electrons in the metal atom

For the given $3 d$-transition metals,

$$ \begin{array}{cccc} V & Fe & Cu & Zn \ 3 d^{3} 4 s^{2} & 3 d^{6} 4 s^{2} & 3 d^{10} 4 s^{1} & 3 d^{10} 4 s^{0} \ n=3 & n=4 & n=0 & n=0 \end{array} $$

$[\because n=$ no. of unpaired electrons $]$

$$ \Delta^{\circ} H _{\text {Atomisation }}\left(kJ mol^{-1}\right)=515 \quad 418 \quad 339 \quad 130 $$

So, absence of unpaired $d$-electrons and larger size of $Zn$ atoms, make the crystal lattice of $Zn$ less closely packed.



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