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Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: user529401 on March 29, 2004, 11:30:47 PM

Title: Why is mercury (I) ion diatomic?
Post by: user529401 on March 29, 2004, 11:30:47 PM

Hello, Why is mercury (I) ion diatomic?

Title: Re:Why is mercury (I) ion diatomic?
Post by: Mitch 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⁺

Title: Re:Why is mercury (I) ion diatomic?
Post by: Mitch 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

Title: Re:Why is mercury (I) ion diatomic?
Post by: AWK 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

Title: Re:Why is mercury (I) ion diatomic?
Post by: Mitch 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?

Title: Re:Why is mercury (I) ion diatomic?
Post by: Mitch on March 30, 2004, 03:06:22 AM

Actually, I think you put up the Hg2N2O8 molecule.  ;)

Title: Re:Why is mercury (I) ion diatomic?
Post by: AWK on March 30, 2004, 03:20:40 AM

Mitch, I added some comment in original post - now all is clear, I hope.
AWK

Title: Re:Why is mercury (I) ion diatomic?
Post by: gregpawin on March 30, 2004, 03:35:31 AM

Huh ???

Title: Re:Why is mercury (I) ion diatomic?
Post by: Julie on March 30, 2004, 09:02:15 AM

What is meant by diatomic ???

Title: Re:Why is mercury (I) ion diatomic?
Post by: AWK on March 30, 2004, 09:08:18 AM

Diatomic is rather inproper in this case, but user52401 probably meant a metal-metal bond.

AWK

Title: Re:Why is mercury (I) ion diatomic?
Post by: gregpawin on March 30, 2004, 08:45:06 PM

So are those atoms in the middle supposed to be nitrogens or mercury atoms?

Title: Re:Why is mercury (I) ion diatomic?
Post by: Mitch on March 30, 2004, 08:55:52 PM

Mercury

Title: Re:Why is mercury (I) ion diatomic?
Post by: gregpawin 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?

Title: Re:Why is mercury (I) ion diatomic?
Post by: Mitch on March 30, 2004, 10:13:42 PM

I don't think so, because it would change the number of valence electrons on Mercury.

Title: Re:Why is mercury (I) ion diatomic?
Post by: AWK 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)

Title: Re:Why is mercury (I) ion diatomic?
Post by: gregpawin on March 31, 2004, 02:21:47 AM

There must be an answer at the quantum level right?  I get this weird twitch when I hear the word intrinsic used to explain stuff... like a chill down my back when biologists and psychologists talk about their discoveries.

Title: Re:Why is mercury (I) ion diatomic?
Post by: Seymor-Omnis on April 01, 2004, 09:07:42 AM

Quote from: AWK on March 30, 2004, 09:08:18 AM

Diatomic is rather inproper in this case, but user52401 probably meant a metal-metal bond.

AWK

I thought metals couldn't bond with other metals of different elements :o, ex. NaK
Unless you are saying the metal bonds with the same metal...I have officially confused myself. ???

Title: Re:Why is mercury (I) ion diatomic?
Post by: gregpawin on April 01, 2004, 11:19:01 AM

Well, still keep in mind electronegativities where elements on the left side like to bond stably with stuff on the right and stuff in the middle is able to bond to most anything... though I'm grossly generalizing here.