Question
What is the order of ionisation energies of the coinage metal
A.
$$Cu > Ag < Au$$
B.
$$Cu > Ag > Au$$
C.
$$Cu < Ag < Au$$
D.
$$Au > Ag < Cu$$
Answer :
$$Cu > Ag < Au$$
Solution :
$$Cu = 3{d^{10}}4{s^1},Ag = 4{d^{10}}5{s^1},Au = 4{f^{14}}5{d^{10}}6{s^1}$$ In all the above given cases, unpaired $$s$$ - electron has to be removed. In the case of $$Cu,$$ a $$4s$$ electron is to be removed which is closer to the nucleus than the $$5s$$ electron of $$Ag .$$
So, $$I{E_1}$$ of $$Cu > I{E_1}$$ of $$Ag.$$
However, in case of $$Au,$$ due to imperfect screening effect of $$14{e^ - }s$$ of $$4f$$ orbitals, the nuclear charge increases and therefore $$5s\,{e^ - }$$ of $$Au$$ is more tightly held.
Thus, the order of $$I{E_1}$$ is $$Cu > Ag < Au.$$