. 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

Best Answer

(A)

In all the 3 case an s– electron in the unpaired state is 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 l.P. decreases from Cu to Ag. However from Ag to Au the 14f electrons are added which provided very poor shielding effect. Then nuclear charge is thus enhanced and therefore the outer electron of Au is more tightly held and so the lP is high.

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