On the other hand, all Cu
II halides are
known except the iodide 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