[Sammy5124]

I have a book that says that when you have copper oxide, and place it with magnesium so that the magnesium gains oxygen to become magnesium oxide, and the copper loses oxygen to become copper, what is happening is:

The magnesium atoms become magnesium ions, and they do this by losing electrons to the copper.

source:
"
Mg(s) + Cu^2+ (s) + O^2- (s) -> Mg^2+ (s) + O^2- (s) + Cu(s)

Look carefully at the equation to see what is being changed. Notice that the oxide ion (O^2-) is completely unaffected by the reaction. It ends up with a different partner, but it is totally unchanged itself. An ion like this is described as a spectator ion.

You don't write spectator ions into the equation because they arn't changed in the reaction.

Mg(s) + Cu^2+ (s) -> Mg^2+ (s) + Cu(s)

Make sure you see how this equation comes from the previous one. This is an ionic equation and shows that the reaction has nothing to do with the oxygen.

What is actually happening is that magnesium atoms are turning into magnesium ions. The magnesium atoms lose electrons to form magnesium ions.

Mg(s) -> Mg^2+ (s) + 2e^-
Those electrons have been gained by copper(II) ions to make the atoms present in metallic copper

Cu^2+ (s) + 2e^ -> Cu(s)

Remember that we are talking about the reaction between copper(II) oxide and magnesium. We have already described this as a redox reaction, but the equations no longer have any oxygen in them"

Now first of all, if magnesium was losing electrons to copper, wouldn't that mean that there is an ionic bond between them?, but since redox reactions can be used to extract and purify metals, I don't see how this can be the case.

Now isn't it really that copper gains its electrons back from the oxygen when its bond to oxygen is broken, and that the magnesium loses its electrons when it bonds to the oxygen - and not that magnesium is losing electrons to copper? I can't understand why it's saying magnesium is losing electrons to copper.

[Borek]

Now first of all, if magnesium was losing electrons to copper, that would mean there is an ionic or metallic bond between them

No. I think you are treating too literally what you were told in the past about synthesis of substances (especially ionic ones). Yes, they can be prepared by reacting elements directly, yes, in such case electrons will move from one element to another creating a bond. No, it is not the only way bonds can be created, no, it doesn't mean each electron transfer requires a bond.

Now isn't it really that copper gains its electrons back from the oxygen when its bond to oxygen is broken, and that the magnesium loses its electrons when it bonds to the oxygen - and not that magnesium is losing electrons to copper? I can't understand why it's saying magnesium is losing electrons to copper.

Even if you were right about the mechanism, the final result would be that the electrons were transferred from the magnesium to copper, so the description would be still pretty accurate. But there is absolutely no reason why the electrons can't be transferred directly.

It will be probably more obvious in solutions - after dissociation ions float completely separately. Imagine you have a solution of any soluble ionic copper salt. Now take a piece of metal (like iron) and dip it into the solution. Iron will become covered with a thin layer of copper almost instantly. The same situation - copper got electrons from the iron, copper got deposited on the surface, iron got oxidized and went in an ionic form into the solution.

[Sammy5124]

I am assuming that the following is true, and this is why I would think electrons cannot be transferred directly:

"It is important to recognize that pure ionic bonding - in which one atom "steals" an electron from another - cannot exist: All ionic compounds have some degree of covalent bonding, or electron sharing. Thus, the term "ionic bonding" is given when the ionic character is greater than the covalent character - that is, a bond in which a large electronegativity difference exists between the two atoms, causing the bonding to be more polar (ionic) than in covalent bonding where electrons are shared more equally."

So if atoms cannot completely steal electrons from each other it stands to reason that
a) there is an ionic bond between the two metals since electrons cannot be completely stolen, or
b) copper gains its electrons back when its bond to the oxygen is broken, and then magnesium loses its electrons to the oxygen

Even though the end result between metals stealing electrons from each other and b) are the same, is there a way to find out which one is correct? As I would prefer to know that my understanding of the mechanism is correct

As for a), I have been told in the past that when a molecule becomes deprotonated, there is still a weak connection between the hydrogen atom, and the original molecule, they are not completely distinct

[Borek]

1. Don't worry about the exact mechanism. And it actually doesn't matter much, as these reactions are very fast and their equilibrium is typically shifted far to one side.

2. As I already told you, in the solution ions are completely separated, so - again - it doesn't matter what compound they were part of. Sure, they are now hydrated, and it is quite likely water molecules somehow take part in charge transfer, but these things are not important enough to be part of the typical GenChem course. Graduate stuff, and even there rarely important.

BTW, have you started with organic chemistry? It is quite common that those who took organic chemistry earlier feel lost when reactions are discussed without mechanism. In inorganic chemistry mechanisms are ignored, period.

As for a), I have been told in the past that when a molecule becomes deprotonated, there is still a weak connection between the hydrogen atom, and the original molecule, they are not completely distinct

That's completely off. Dissociation means complete separation.

[Arkcon]

If you're really looking forward to a through explanation of redox mechanisms, you might try to find access to this publication, written by a Nobel-prize laureate:  http://pubs.acs.org/doi/pdf/10.1021/ed045p452

[Sammy5124]

BTW, have you started with organic chemistry? It is quite common that those who took organic chemistry earlier feel lost when reactions are discussed without mechanism. In inorganic chemistry mechanisms are ignored, period.

Not yet, but I find the easiest way to remember something is to understand the mechanism behind how it works which is why I was trying to do so.

As for a), I have been told in the past that when a molecule becomes deprotonated, there is still a weak connection between the hydrogen atom, and the original molecule, they are not completely distinct

That's completely off. Dissociation means complete separation.

I have asked this question here, and I got the following answer. Does it seem incorrect?

http://answers.yahoo.com/question/index?qid=20131130064419AAZygaR

Taking your example of nitric acid losing a hydrogen and forming a nitrate anion, according to your hypothesis, one should then be able to isolate the nitrate anion, if it were not in any way, shape, or form, associated with the proton (H+). Do you think this is actually possible? Can you have a pure positive (or negative) species without something else being associated with it? I think this is why it is stated that you can not have a 100% pure, true ionic bond. There will always be some finite association of the electrons between the two ions.

If you're really looking forward to a through explanation of redox mechanisms, you might try to find access to this publication, written by a Nobel-prize laureate:  http://pubs.acs.org/doi/pdf/10.1021/ed045p452

That seems to require money to read. I was hoping the reaction would be something simple such as the bond between the copper and the oxygen breaks giving the copper its electrons back, and then the oxygen bonds with the magnesium, making the magnesium an ion. But if it's something much more complex that requires reading a graduate thesis to understand..

[Borek]

The answer at Yahoo looks OK to me, but I just skimmed.

You can separate single ions, or even some small amount of ions, especially in gaseous phase. However, try to estimate with what force will 1 mole of positively charged ions attract 1 mole of negatively charged ions. Let's say they are separated by 1 m.

Also note that electrostatic attraction between charged ions doesn't mean a bond exists.