Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: johnson039 on 05/01/2009 14:58:19
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do ammonium ions consist of coordinate covalent bond?
or without that? [???]
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do ammonium ions consist of coordinate covalent bond?
or without that? [???]
I would say yes. According to the definition I know (someone corrects me if I'm wrong) a covalent bond is called coordinative if the number of bonds formed by the atom is greater than the absolute value of its oxidation number.
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Only one of the bonds in the ammonium ion (NH4+) is a coordinate covalent bond (or dative bond) where both electrons are donated by nitrogen, the other three bonds are covalent bonds. [:)]
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Here is a (not very well drawn) diagram
[diagram=386_0]
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You might also want to take note of the fact that once the dative bond is formed, you can't differentiate it from the other bonds.
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is it correct for drawing the following diagram?
where the positive sign is the formal charge[diagram=387_0]
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Yes, if thats the way you have been taught
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I would say yes. According to the definition I know (someone corrects me if I'm wrong) a covalent bond is called coordinative if the number of bonds formed by the atom is greater than the absolute value of its oxidation number.
I've read in my old book of General Chemistry and it says that in a coordination compound = complex, the central ion must have a positive oxidation state, so this would exclude nitrogen in NH4+.
It's written that "a coordination compound is a compound in which the central atom forms a number of σ bonds greater than its oxidation number when this is positive".
Edit: Not only positive, also zero.
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a number of σ bonds greater than its oxidation number when this is positive".
You mean when the oxidation number is positive?
Never mind, I know what you mean now. Hmm... [:-\]
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That sounds more like a complex-ion definition, but it's a text book so I can't argue. But what about acid-base reactions like trimethylamine with aluminium chloride?
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But what about acid-base reactions like trimethylamine with aluminium chloride?
What do you mean?
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The term complex in chemistry, also called a "coordination compound" or "metal complex", a structure consisting of a central atom or molecule connected to surrounding atoms or molecules. Originally, a complex implied a reversible association of molecules, atoms, or ions through weak chemical bonds. As applied to coordination chemistry, this meaning has evolved. Some metal complexes are formed virtually irreversibly and many are bound together by bonds that are quite strong.
http://en.wikipedia.org/wiki/Complex_(chemistry)
Whereas we're talking about a co-ordination covalent bond, in which both electrons are donated by one atom. So its pretty confusing to tell the difference between the two [???] [???] [???]
So Mr. lancenti was correct [:)]
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That sounds more like a complex-ion definition, but it's a text book so I can't argue. But what about acid-base reactions like trimethylamine with aluminium chloride?
If you tell me what compound forms I can answer you. If Al forms more than 3 bonds with the nitrogen in (CH3)3N and the Cl- then it's a complex and so a coordinative compound for sure.
However there is no need to take (CH3)3N as ligand, you can take NH3, CN-, OH- or many others. Even H2O. All the following are coordinative compounds (= complexes):
[Cu(H2O)6]2+
[Cu(NH3)4]+
[Fe(CN)6]4-
[Co(NH3)6]3+
[Zn(OH)4]2-
[Al(H2O)4(OH)2]+
[FeF6]3-
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A diagram always helps [:)]
[diagram=388_0]
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If Aluminum trichloride reacts with some ligand, of course it will form more than 3 bonds and so will be a coordinative compound.
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The term complex in chemistry, also called a "coordination compound" or "metal complex", a structure consisting of a central atom or molecule connected to surrounding atoms or molecules. Originally, a complex implied a reversible association of molecules, atoms, or ions through weak chemical bonds. As applied to coordination chemistry, this meaning has evolved. Some metal complexes are formed virtually irreversibly and many are bound together by bonds that are quite strong.
http://en.wikipedia.org/wiki/Complex_(chemistry)
Whereas we're talking about a co-ordination covalent bond, in which both electrons are donated by one atom. So its pretty confusing to tell the difference between the two [???] [???] [???]
So Mr. lancenti was correct [:)]
as you 've said, both electrons are donated by one atom.in the NH4+ case, the empty orbital of the H+ ion is filled by the electrons from the N rite?
so, here comes the question, can H2O be considered as OH- ion dative bond to the H+.
that's the question annoying me, confusing me.
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so, here comes the question, can H2O be considered as OH- ion dative bond to the H+. that's the question annoying me, confusing me.
Think about a simple acid-base reaction, one of the products is water, and this is formed by OH- reacting with H3O+ as such:
[diagram=389_0]
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So when you think about it like that the answer to your question would be "Yes"
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as you 've said, both electrons are donated by one atom.in the NH4+ case, the empty orbital of the H+ ion is filled by the electrons from the N rite?
so, here comes the question, can H2O be considered as OH- ion dative bond to the H+.
that's the question annoying me, confusing me.
According to the definition I have in my book, it's not a coordinative compound (so the bonds are note dative), because the H+ doesn't form more bonds than its oxidation number.
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Just because there are dative bonds does not mean that the compound definitely is a complex (coordinative compound).
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Just to clarify...
Ligands are only called ligands when they form coordinate covalent bonds with a metal ion, right? Or are they called ligands even though they form a bond with another covalent compound?
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Bonding between the central atom or ion and the ligand is either an ion-dipole bond or a dative bond.
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The cluster of water molecules around non-transition ions such as sodium, magnesium and aluminium is the result of the electrostatic attraction between the ion and the partial charge on the oxygen of the water molecule. This type of bond is referred to as an ion-dipole interaction. They are much weaker than ionic or covalent bonds, and their strength depends mainly upon the size and charge of the ion.
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The cluster of water molecules around non-transition ions such as sodium, magnesium and aluminium is the result of the electrostatic attraction between the ion and the partial charge on the oxygen of the water molecule. This type of bond is referred to as an ion-dipole interaction. They are much weaker than ionic or covalent bonds, and their strength depends mainly upon the size and charge of the ion.
If we consider Iron (III) ions hydrated, we get the hexa-aqua complex, [Fe(H2O)6]3+. When we draw the complex we get an octahedral molecular geometry which we do not get with sodium (I do not know why). Also, the bond is so strong that it is able to move electron density OUT of the water molecules thus resulting in the acidity of the Iron (III) ions. Does this not then mean that the dative bond between iron and the oxygen atom is quite strong?
H H
/ /
Fe<--:O: <--> Fe<--:O: + H+
\ ..
H
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I am not sure what you are trying to say. Yes, what you have said is all correct but what I said was that ion-dipole interaction occurs between non-transition ions such as sodium, magnesium and aluminium.
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As I showed in a previous post, even water is a ligand:
http://en.wikipedia.org/wiki/Ligand
http://en.wikipedia.org/wiki/Complex_(chemistry)
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Just to clarify...
Ligands are only called ligands when they form coordinate covalent bonds with a metal ion, right? Or are they called ligands even though they form a bond with another covalent compound?
For example?
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As I showed in a previous post, even water is a ligand:
http://en.wikipedia.org/wiki/Ligand
http://en.wikipedia.org/wiki/Complex_(chemistry)
Umm... I am not sure what you are trying to say here Mr. lightarrow [:-\] Are you addressing me or Mr. lancenti.
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As I showed in a previous post, even water is a ligand:
http://en.wikipedia.org/wiki/Ligand
http://en.wikipedia.org/wiki/Complex_(chemistry)
Umm... I am not sure what you are trying to say here Mr. lightarrow [:-\] Are you addressing me or Mr. lancenti.
No, I just intended to try to clarify the subject a little bit (even to myself [;)]). I think that when water or another species acts as ligand, a covalent bond have to form, so, as you say, the bond of water with ions as Na+ in the solvation shoudn't be considered as coordinative, that is, those compounds shouldn't be considered as complexes.