Why can Copper have both a +1 and +2 oxidation state?
3 answers
Because it can lose either 1 or 2 electrons.
Yeah, I know that, but why can Copper lose either one or two while cadmium only has a +2 OS. I think the answer has something to do with valence electrons, but I'm not sure exactly.
I think the comparison you are making is not a valid one for Cd has an electron configuration of [Kr]4d10 5s2. It is easy enough to see that Cd loses the two outside (valence) electrons and does not have a great tendency to delve into the lower 4d10 shell (which we usually think of as closed). Cd is quite similar to Zn ion in this respect. Thus the common oxidation state for both Zn and Cd is +2.
I think the pertinent question you may be asking is why does Cu lose two electrons at all? And why aren't most copper compounds Cu+1 and not Cu+2 since the electron configuration is
1s2 2s2 2p6 3s2 3p6 3d10 4s1 = 29.
It is easy enough to understand why copper loses a single electron to form +1 copper compounds. Why it loses two is much much more complex. It turns out that there are MANY more compounds of Cu+2 than of Cu+1 which makes it even more confusing. The answer lies mostly in the environment in which copper finds itself. The solvation energy of the +2 ion (for solutions), the lattice energy of solid Cu+2 vs Cu+1 compounds, and the ability to form complex ions with the d,s, and p orbitals (with variable stabilities), all favor the +2 ion. That isn't a definitive answer, I know, but it may give you some insight into what is going on. The best answer I can give, which, again, is not definitive, is that "that is the nature of the beast." The main reason this can happen is because the relative energy levels of the 3d and 4s orbitals when they are almost or completely filled is so close to each other that the deciding factor is what complex or what compound is being formed. I hope this helps.
I think the pertinent question you may be asking is why does Cu lose two electrons at all? And why aren't most copper compounds Cu+1 and not Cu+2 since the electron configuration is
1s2 2s2 2p6 3s2 3p6 3d10 4s1 = 29.
It is easy enough to understand why copper loses a single electron to form +1 copper compounds. Why it loses two is much much more complex. It turns out that there are MANY more compounds of Cu+2 than of Cu+1 which makes it even more confusing. The answer lies mostly in the environment in which copper finds itself. The solvation energy of the +2 ion (for solutions), the lattice energy of solid Cu+2 vs Cu+1 compounds, and the ability to form complex ions with the d,s, and p orbitals (with variable stabilities), all favor the +2 ion. That isn't a definitive answer, I know, but it may give you some insight into what is going on. The best answer I can give, which, again, is not definitive, is that "that is the nature of the beast." The main reason this can happen is because the relative energy levels of the 3d and 4s orbitals when they are almost or completely filled is so close to each other that the deciding factor is what complex or what compound is being formed. I hope this helps.
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