In this case, Cu
2+ oxidises I
– to I2:
 
2
2 2
2
2Cu
4I
Cu I
I
s





However, many copper (I) compounds are unstable in aqueous
solution and undergo disproportionation 2Cu
+ ® Cu
2+ + Cu
The stability of Cu
2+ (aq) rather than Cu
+(aq) is due to the much
more negative DhydH
o of Cu
2+ (aq) than Cu
+, which more than
compensates for the second ionisation enthalpy of Cu The ability of oxygen to stabilise the highest oxidation state is
demonstrated in the oxides The highest oxidation number in the oxides
(Table 4