What is the order of ionisation energies of the coinage metal

What is the order of ionisation energies of the coinage metal
  1. $\quad \mathrm{Cu}>\mathrm{Ag} < \mathrm{Au}$
  2. $\quad \mathrm{Cu}>\mathrm{Ag}>\mathrm{Au}$
  3. $\mathrm{Cu} < \mathrm{Ag} < \mathrm{Au}$
  4. $\quad \mathrm{Ag}>\mathrm{Au} < \mathrm{Cu}$

Solution

$\mathrm{Cu}=3 d^{10} 4 s^{1}, \mathrm{Ag}=4 d^{10} 5 \mathrm{~s}^{1}, \mathrm{Au}=4 f^{14} 5 d^{10} 6 s^{1}$
In all the above given cases, unpaired $s$ -electron has to be removed. In the case of $\mathrm{Cu}$, a $4 s$ electron is to be removed which is closer to the nucleus than the $5 s$ electron of $\mathrm{Ag}$.
So, $\mathrm{IE}_{1}$ of $\mathrm{Cu}>\mathrm{IE}_{1}$ of Ag.
However, in case of Au, due to imperfect screening effect of $14 \mathrm{e}^{-} s$ of $4 f$ orbitals, the nuclear charge increases and therefore 5s $\mathrm{e}^{-}$ of $\mathrm{Au}$ is more tightly held. Thus, the order of $\mathrm{IE}_{1}$ is $\mathrm{Cu}>\mathrm{Ag} < \mathrm{Au}$. .

Asked in: JEE-TOPICTESTS-CHEMISTRY

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