All the c− o bonds in carbonate ion are equal in length. Explain.
Answers
In Carbonate ions, the 4 p-orbitals of the 4 atoms overlap. This basically means that all 4 p-orbitals of the double-bonds sort of join together at the central atom in this case, the Carbon atom. Why is this the case?
Two of the three Oxygen atoms in the Carbonate ion has an extra electron which makes its overall charge -2. When electrons linger at atoms which don’t compensate for its charge, they’d rather form a bond with another electron from another atom essentially staying in between the atoms so that its charge would be spread between the two. It’s not the most precise analogy but roughly that’s how it works. When these two electrons pair up in the centre of the Carbon and Oxygen atoms, their orbitals, one of the p-orbitals, overlap, thus forming a pi-bond.
However, as I mentioned earlier, there is another Oxygen atom that wants to do the same. Yet, Carbon can only have 4 bonds around it. If the other Oxygen would form another pi-bond with the Carbon, it would have 5! That is including the other single-bonded oxygen. Both of these single bonded Oxygens have a charge of -1 due to the excess electron thus both would strive to get a spot in Carbon’s p-orbital.
Therefore, we can now say that at any given time, there is going to be a double-bonded Oxygen and 2 single bonded, negatively charged Oxygens. However, again, two of these Oxygens will fight to get that double bond. Thus, by mere random chance, one of the two Oxygens will get to get it with the Carbon at the same time knocking out the electron of the pi-bond of the previously double bonded Oxygen and returning it to it.
The location of the double bond has now changed. But the same thing will soon happen again, very, very quickly, millions of times a second to the extent that the changing of the bonds is practically undetectable.
Intuitively, you can assume that while the electrons move to change the position of the double bonds, the bond lengths will get shorter or longer according to whether they are leaving or entering the are between the atoms.
And, YOU ARE CORRECT.
The bond lengths are the same because of this continuous position shift in the double bond. Lets be clear, they do change a bit but the shift in the position of the double bond is very quick that they practically seem constant and seem to be everywhere. Because of this, we simply assume that the pi-bonds therefore the pi-orbitals of all atoms have been merged together, out of sheer convenience. Haha.
Do note however that THERE IS NO TRUE FORMATION OF A SINGLE OR DOUBLE BOND. This is because just before the bond length increases to the length or a single bond or decreases to the length of a double bond, the exact opposite occurs. Again, this happens very quickly. This is why the bond length, as you might have been taught, is in between the length of a single bond and a double bond.