In each of the following pairs of salts, which one is more stable and why ? (i) Ferrous and ferric salts (ii) Cuprous and cupric salts.

In each of the following pairs of salts, which one is more stable and

1.	In each of the following pairs of salts, which one is more stable and why ? (i) Ferrous and ferric salts (ii) Cuprous and cupric salts.
Answer» Solution :(i) Electronic configuation Fe atom (Z = 26) is `1s^(2) 2s^(2) 2p^(6) 3s^(2) 3p^(6) 3d^(6) 4s^(2)` `:.` Electronic configuration of `Fe^(2+)` ion `= 1s^(2) 2s^(2) 2p^(6) 3s^(2) 3p^(6) 3d^(6)` Electronic configuration of `Fe^(3+) " ion " = 1s^(2) 2p^(6) 3s^(2) 3p^(6) 3d^(5)` As half-filled `3d^(5)` configuration is more stable, THEREFORE, ferric salts are more stable then ferrous salts. (ii) Electronic configuration of Cu atom `(Z = 29) = 1s^(2) 2^(2) 2p^(6) 3s^(2) 3p^(6) 3d^(10) 4s^(1)` `:.` Electronic configuration of `Cu^(+) " ion " 1s^(2) 2s^(2) 2p^(6) 3s^(2) 3p^(6) 3d^(10)` Electronic configuration of `Cu^(2+) " ion " = 1s^(2) 2s^(2) 2p^(6) 3s^(2) 3p^(6) 3d^(9)` Although `Cu^(+)` has fully-filled d-orbital, YET cuprous salts are LESS stable. This is because the nuclear charge is not sufficient enough to hold 18 electrons of `Cu^(+)` ion present in the outermost shell.