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Why does copper have a stable oxidation state of +2 whereas silver has a stable oxidation state of +1 and gold +3 and they all belong to the same group?

Why does copper have a stable oxidation state of +2 whereas silver has a stable oxidation state of +1 and gold +3 and they all belong to the same group?

Grade:12th pass

2 Answers

Arun
25750 Points
4 years ago
The term stability is basically a relative term,yes Cu(+2) is more stable than Cu(+1),and that is because there are more factors than just ionisation energy which are responsible for the stability of a particular state.

The determining factor here is the much higher hydration energy of Cu2+(-2100kJ/mol)than Cu+1(-580kJ/mol) due to the smaller size and higher charge of Cu2+ leading to higher charge density. This gap is sufficient enough to compensate for the higher 2nd Ionisation energy of Cu,that is why compared to +1state Cu+2 is more stable.

I also would like to add,tentatively,that there should be a bit of contribution from CFSE,in the aquoeas solution.For,Cu1+,the configuration 3d10 yields 0 CFSE but for Cu2+,there is quite a contribution of CFSE as the d9 system is prone to Jahn Teller distortion and this distortion is known to increase stability by increasing CFSE.This works for Au as well,the balance toward Au(+3) is not only due to gain in hydration energy but also due to a large gain in CFSE. It has more effect in Au than Cu as Au is a 3rd row transition element for which CFSE value is nearly 80% greater than a 1st row transition element like Cu
TEJA KRISHNA
42 Points
4 years ago
The term stability is basically a relative term,yes Cu(+2) is more stable than Cu(+1),and that is because there are more factors than just ionisation energy which are responsible for the stability of a particular state.The determining factor here is the much higher hydration energy of Cu2+(-2100kJ/mol)than Cu+1(-580kJ/mol) due to the smaller size and higher charge of Cu2+ leading to higher charge density. This gap is sufficient enough to compensate for the higher 2nd Ionisation energy of Cu,that is why compared to +1state Cu+2 is more stable.I also would like to add,tentatively,that there should be a bit of contribution from CFSE,in the aquoeas solution.For,Cu1+,the configuration 3d10 yields 0 CFSE but for Cu2+,there is quite a contribution of CFSE as the d9 system is prone to Jahn Teller distortion and this distortion is known to increase stability by increasing CFSE.This works for Au as well,the balance toward Au(+3) is not only due to gain in hydration energy but also due to a large gain in CFSE.

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