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:
- 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.
