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Topic: Why is mercury (I) ion diatomic?  (Read 37923 times)

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user529401

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Why is mercury (I) ion diatomic?
« on: March 29, 2004, 11:30:47 PM »
Hello, Why is mercury (I) ion diatomic?

Offline Mitch

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Re:Why is mercury (I) ion diatomic?
« Reply #1 on: March 30, 2004, 12:38:48 AM »
Why Mercury(I) is diatomic is an excellent question that I'm not sure is well understood. It goes against the trend in that group, Zinc and Cadmium don't behave like this. The obvious answer to give you is that the 4f electrons shield the 4s electrons poorly, so it can ionize to Hg2+ readily.

A more qualitative answer is that this ion is not found in nature as Hg2+, but as salts like Hg2(H2O2)22+
« Last Edit: March 30, 2004, 12:47:23 AM by Mitch »
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Offline Mitch

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Re:Why is mercury (I) ion diatomic?
« Reply #2 on: March 30, 2004, 12:46:06 AM »
Forgot to put the references. I took some of the above information from Advanced Inorganic Chemistry fith edition by Cotton and Wilkinson page 601.

And also from W. R. Mason, Inorg. Chem., 1983, 22, 147
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Re:Why is mercury (I) ion diatomic?
« Reply #3 on: March 30, 2004, 02:52:31 AM »
Scientists answer for troublesome question is always "good (or excelent of fascinating) question. Mitch, this is not a cutting remark to your answer, this is real truth.

This is structure of Hg2(H2O)22+ . 2NO3- (water hydrogen atoms are not included in ICSD - very old work). Note, there are covalent and ionic bonds between Hg and O atoms (lengths are in Angstrems, drawn in Mercury 1.2)
Oxygen -red
Nitrogen - blue
Mercury - violet


« Last Edit: March 30, 2004, 09:09:35 AM by AWK »
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Offline Mitch

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Re:Why is mercury (I) ion diatomic?
« Reply #4 on: March 30, 2004, 03:02:42 AM »
Do you have too many atoms? I count 12? Can you tell us what the colors are?
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Offline Mitch

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Re:Why is mercury (I) ion diatomic?
« Reply #5 on: March 30, 2004, 03:06:22 AM »
Actually, I think you put up the Hg2N2O8 molecule.  ;)
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Offline AWK

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Re:Why is mercury (I) ion diatomic?
« Reply #6 on: March 30, 2004, 03:20:40 AM »
Mitch, I added some comment in original post - now all is clear, I hope.
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Offline gregpawin

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Re:Why is mercury (I) ion diatomic?
« Reply #7 on: March 30, 2004, 03:35:31 AM »
Huh ???
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Julie

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Re:Why is mercury (I) ion diatomic?
« Reply #8 on: March 30, 2004, 09:02:15 AM »
What is meant by diatomic ???

Offline AWK

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Re:Why is mercury (I) ion diatomic?
« Reply #9 on: March 30, 2004, 09:08:18 AM »
Diatomic is rather inproper in this case, but user52401 probably meant a metal-metal bond.

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Offline gregpawin

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Re:Why is mercury (I) ion diatomic?
« Reply #10 on: March 30, 2004, 08:45:06 PM »
So are those atoms in the middle supposed to be nitrogens or mercury atoms?
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Offline Mitch

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Re:Why is mercury (I) ion diatomic?
« Reply #11 on: March 30, 2004, 08:55:52 PM »
Mercury
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Offline gregpawin

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Re:Why is mercury (I) ion diatomic?
« Reply #12 on: March 30, 2004, 09:14:31 PM »
So each atom is attached to a nitrate ion and water molecule?  It doesn't separate from the nitrate?
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Offline Mitch

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Re:Why is mercury (I) ion diatomic?
« Reply #13 on: March 30, 2004, 10:13:42 PM »
I don't think so, because it would change the number of valence electrons on Mercury.
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Offline AWK

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Re:Why is mercury (I) ion diatomic?
« Reply #14 on: March 31, 2004, 12:23:44 AM »
Dative bond between oxygen atom from water and mercury atom is short. Ionic contact between nitrate oxygen atom and mercury atom is longer. I drew only the shortest contacts from crystal structure of mercury(II) nitrate dihydrate, but note this is not one molecule. There are two nitrate anions and one Hg2(H2O)22+ cation.
Concerning primary question - scientist cannot simply explain why mercury(I) form metal-metal bond.
So this is called intristic property of this element. Other elements (but probably not all) also can form chains or rings consisted of  bonds between atoms of the same element (eg. B, C, N, O, Si, S, Se and so on)
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