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Is it covalent or coordinate covalent bond? Because it can be a bond between $\ce{O}$ and two $\ce{H}$ atoms and so it will be covalent bond. And it can be a bond between $\ce{H+}$ ion and $\ce{OH-}$ ion and it will be coordinate covalent bond?

If covalent, why not coordinate covalent? And if coordinate covalent, why not covalent?

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Fatima Elzahra
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    There is no difference between an 'ordinary' covalent bond and a 'coordinate' covalent bond. As your structures show, they are just two ways of looking at the exact same thing. – orthocresol Dec 30 '18 at 09:59
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    The difference is that, in coordinate covalent bond the 2 shared electrons are from one atom (O) , while in ordinary covalent bond the 2 shared electrons are from the 2 atoms (one from O, and the other from H) – Fatima Elzahra Dec 30 '18 at 11:27
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    And how is the molecule supposed to know where the electrons are coming from? The electrons don't come with labels attached. – orthocresol Dec 30 '18 at 11:42
  • Yeah they don't . But in coordinate covalent ,the bond is between hydroxide ion and hydrogen ion . While in ordinary covalent bond ,the bond is between atoms . – Fatima Elzahra Dec 30 '18 at 11:51
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    Well it will depend on whether the water is formed from $\ce OH^- + H^+ \rightarrow H_2O$ or from $2H_2+O_2 \rightarrow 2H_2O$. Are hydrogen atoms or hydrogen ions forming the water - this decides whether the hydrogen has an electron to use in the bond forming process. – H.Linkhorn Dec 30 '18 at 15:43
  • https://chemistry.stackexchange.com/questions/21709/why-does-coordinate-covalent-bond-form – Mithoron Dec 30 '18 at 17:19
  • Thank you for all of you ,I have read this https://chemistry.stackexchange.com/questions/21709/why-does-coordinate-covalent-bond-form# , but still I don't understand which one is right ... or you mean both are possible(it can form coordinate and ordinary covalent bonds)??! H.Linkhorn , Mithoron , Tyberius. – Fatima Elzahra Dec 31 '18 at 09:38
  • Nothing change. You can form water even attaching a OH- and a H+. Would you really conclude that you have a covalent bond and an ionic one in water? Probably not. – Alchimista Dec 31 '18 at 15:27
  • There's no such thing as dative bond creation between cation and anion, that's it. – Mithoron Dec 31 '18 at 19:38
  • @Mithoron thank you so much . Then when do we form dative covalent bond (between what ?).... Do you also mean that , dative bond is not formed if an ordinary covalent bond can be formed ? – Fatima Elzahra Jan 02 '19 at 09:35
  • @Alchimista thank you so much .. I don't mean ionic bond , I mean ordinary covalent bond and coordinate covalent bond. If they were both possible to be formed in water , then i don't think there's a problem by concluding that I have an ordinary and a coordinate covalent bonds in water ! (Because it sounds strange ,that's why I am asking .I must've understood something wrong ) – Fatima Elzahra Jan 02 '19 at 09:43
  • We are try to say something that otherwise stated might sound rude. Your distinction inside the same and symmetric molecule is senseless! As I said why not to conclude that one bond is ionic then? We are all repeating the same in slightly different way. What you sketch as a dative bond is right the same covalent bond as sketched above. You should see that. – Alchimista Jan 02 '19 at 12:14

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The water molecule is symmetrical. The two bonds in it are the same and cannot be distinguished. It makes little sense to label them as different types of bond.

Since the bonds are symmetric, the electron distributions will be the same. We can't tell, nor do we care, where the electrons "came from" and all we can tell is that electrons are shared between hydrogen and oxygen to create the bonds.

So the distinction between covalent and coordinate-covalent is irrelevant for the water molecules and does not help us understand anything about it.

matt_black
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  • Thank you so much .If water has two same and symmetric bonds ( that means it can't have 1 coordinate and 1 ordinary bond ),that means it has 2 ordinary covalent bond ,right ?.....how the distinction between the 2 bonds is irrelevant ?water has covalent bond (covalent bonds can be ordinary or coordinate or polar... ),so I just want to know ,is the bond in H2O actually ordinary or coordinate or both are possible?[because when I used rules , both (ordinary and coordinate) were possible I think (as shown in the picture above )] – Fatima Elzahra Dec 31 '18 at 09:57
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    @FatimaElzahra My point is that it is a simple covenant bond and any attempt to classify it as some particular type of covalent bond isn't going to help understand it in any way. – matt_black Dec 31 '18 at 20:24
  • ok thanks a lot .. You mean it is not useful to classify it ,but I just think it is strange to have 2 different possible types of bonds in water , and I thought one of them is maybe wrong . That's why I am asking :) – Fatima Elzahra Jan 02 '19 at 09:55
  • @Fatima Elzahra again in your reasoning there could be even an ionic one. Is the distinction that does make sense / isn't useful. – Alchimista Jan 02 '19 at 12:19
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Perhaps it helps.

Let's take two hydrogen and one oxygen atoms. They come together and react to form water by covalent bonds involving their valence electrons. Fine.

Now let us take a proton and an OH- ion. The ion will "datively" share is lone pair to the proton and water is formed. Again fine.

How do you resolve now what O-H bond is what? They are the same type of bond and does not help nor does have sense to make a distinction between them.

It is exactly what you have sketched. But the arrowed bond is not meaningful anymore as for the two electrons are one from O and one from H, nothing can keep track of history here.

Or as said in a comment: no concept on having a dative bond between ions.

Alchimista
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