Science Forums
User Name
Password
Science Social Network
home    members    help/rules    who is online    contact   

Go Back   Science Forums > Physical Sciences Forums > Chemistry
Become a science forums sponsor today
Reply
 
LinkBack Thread Tools
Old 03-12-2007   #1 (permalink)
Little Bang's Avatar
Explaining


 



Water

Can anyone give me the current explanation of why there is a 104.45 degrees between the hydrogen bonds of water?
Reply With Quote
Old 03-12-2007   #2 (permalink)
Michaelangelica's Avatar
Creating


 



Smile Re: Water

Ask
HydrogenBond he is sure to know.


----------------
What could possibly go wrong!?
DOCTOR WHO
Reply With Quote
Old 03-12-2007   #3 (permalink)
Monomer's Avatar
Explaining


 



Re: Water

This is why...

Quote:
In the water molecule H2O, the single electron of each H is shared with one of the six outer-shell electrons of the oxygen, leaving four electrons which are organized into two non-bonding pairs. Thus the oxygen atom is surrounded by four electron pairs that would ordinarily tend to arrange themselves as far from each other as possible in order to minimize repulsions between these clouds of negative charge. This would ordinarly result in a tetrahedral geometry in which the angle between electron pairs (and therefore the H-O-H bond angle) is 109°. However, because the two non-bonding pairs remain closer to the oxygen atom, these exert a stronger repulsion against the two covalent bonding pairs, effectively pushing the two hydrogen atoms closer together. The result is a distorted tetrahedral arrangement in which the H—O—H angle is 104.5°.

Water and its structure
Reply With Quote
Old 03-17-2007   #4 (permalink)
Larv's Avatar
Thinking


 



The geometry of water

Quote:
Originally Posted by Monomer View Post
This is why...
Quote:
In the water molecule H2O...The result is a distorted tetrahedral arrangement in which the H—O—H angle is 104.5°.
From: Water and its structure
Over what lapse of time do you suppose this water tetrahedron actually exists geometrically? Maybe liquid water never attains such a geometry (in a temporal sense), but I'm not entirely sure. Am I right or wrong?

—Larv
Reply With Quote
Old 03-17-2007   #5 (permalink)
Mercedes Benzene's Avatar
Medicinal Chemist

Hypography Staff Member
Moderator
Editor

 



Re: Water

Quote:
Over what lapse of time do you suppose this water tetrahedron actually exists geometrically? Maybe liquid water never attains such a geometry (in a temporal sense), but I'm not entirely sure. Am I right or wrong?
Why would it NOT attain the geometry that it does??
And a water molecule IS NOT a tetrahedron.


----------------
Moderator -- Chemistry, Biology, Watercooler, Competitions, Architecture.
Reply With Quote
Old 03-17-2007   #6 (permalink)
Larv's Avatar
Thinking


 



Re: Water

Quote:
Originally Posted by Mercedes Benzene View Post
Why would it NOT attain the geometry that it does??
And a water molecule IS NOT a tetrahedron.
Because it's an electromagnetic thing that doesn't fixed a geometry?
However, like you, I don't think it is a tetrahedron, if there is a fixed geometry. My gross model of a water molecule is a softball with two dimes stuck to its surface, separated by 104.5 degrees of the softball's circumference. My understanding of this water-molecule model is that the dimes are never in a fixed location with respect to the softball, but rather "floating" on its electron clouds.

—Larv
Reply With Quote
Old 03-19-2007   #7 (permalink)
HydrogenBond's Avatar
Creating


 



Re: Water

The angle discussed is true for an isolated water molecule. The unbonded electrons repel each other, forcing the hydrogen to get a little closer than a tetrahedron. The extra strain put on the hydrogen is a reflection of the higher electronegativity of oxygen. Oxygen wants the electrons more and isn't going to make it easy for hydrogen.

When you talk about hydrogen bonding angle, this is different, since it involves more than one water molecule. The tetrahedral of OH- bonds does form in some versions of ice because water will expand as ice. The hydrogen gets the better tetrahedral angle but loses something by being pushed further away during expansion. Oxygen is still being stubborn with electrons, so it gives and takes.

The thing about hydrogen bonds is that a hydrogen bond is maximized if it form a nice straight line with the shared electrons on another water. 180degrees. The tetrahral in ice allows all the hydrogen bonds to line up in straight lines. Beiing pushed away to reflect expansion, puts them at the correct distance for partial covalent bonding to also form. This is how the oxygen gets even and assert its higher electronegativity.

In liquid water, the tetrahedral state is not as common. Water forms all type of random and extended structure. But hydrogen just can't stay very long in the tetrahedral. With water denser than ice, the oxygen can't push hydrogen away for the tetrahedral to be stable, so hydrogen assumes placement that is less then a perfect tetrahedral. What this does, is make the average hydrogen bond angle with the shared electrons different than 180, with bond strength falling off rapidly with deviation from linearity. This is another trick by oxygen to assert its higher electronegativity.

Last edited by HydrogenBond; 03-19-2007 at 02:52 PM.
Reply With Quote
Old 03-19-2007   #8 (permalink)
freeztar's Avatar
Wedding Planner

Hypography Staff Member
Moderator
Editor
Silver Subscription
Sponsor

Latest blog entry:
Things to bring
 
freeztar has a reputation beyond reputefreeztar has a reputation beyond reputefreeztar has a reputation beyond reputefreeztar has a reputation beyond reputefreeztar has a reputation beyond reputefreeztar has a reputation beyond reputefreeztar has a reputation beyond reputefreeztar has a reputation beyond reputefreeztar has a reputation beyond reputefreeztar has a reputation beyond reputefreeztar has a reputation beyond repute
 



Question Re: Water

Quote:
Originally Posted by HydrogenBond View Post
With water denser than ice,


I thought solid form was always more dense than liquid...
But I guess it does make sense if you consider the strange fact that ice expands. Am I thinking right on this?


----------------
Hypography Science Forums Moderator
---
"There are no passengers on Spaceship Earth. We are all crew." - Marshall McLuhan

"We must not forget that when radium was discovered no one knew that it would prove useful in hospitals. The work was one of pure science. And this is a proof that scientific work must not be considered from the point of view of the direct usefulness of it." - Marie Curie
Reply With Quote
Old 03-20-2007   #9 (permalink)
LJP07's Avatar
Explaining


 



Re: Water

Generally, when you take into account the electronegativity mentioned above, normally, in compounds like Boron Trichloride and Ammonia, Water etc, you would take 2.5 ( or 2.75, normally 2.5) degrees approximately for each lone pair that exists, so whereas the normal bond angle is 109 Degrees, the two lone pairs ( 4 electrons not involved in bonding ) make this 104 degrees approx. This gives a distorted tetrahedral or Pyramidal Shape to the molecule.
Reply With Quote
Old 03-20-2007   #10 (permalink)
hallenrm's Avatar
A different person


 



Re: Water

The primary reason why scientists believe that the angle between two O-H bonds in a water molecule is 104.5 degrees is that only if we believe so that we can explain various observed properties of water. Electronagetivity, electron pairs, tetrahedrals etc. are all secondary!


----------------
While engaged in the persuit of the truth be ready for the unexpected.
Change alone is unchanging.
Reply With Quote
Reply

Bookmarks


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
Water: Where will it come from in 2050? Michaelangelica Earth science 142 4 Days Ago 12:40 PM
Water+ orbsycli Earth science 14 03-15-2007 02:52 PM
Water contaminates and sex Cedars Earth science 3 01-21-2007 06:27 AM
nowhere of water droplets? insight Physics and Mathematics 39 11-05-2005 02:47 PM
Water Gabriella Philosophy of Science 9 08-31-2005 06:02 PM


All times are GMT -8. The time now is 07:48 AM.

Hypography?

Hypography [n.]: A combination of "hyperlink" and "bibliography" - ie, a list of links to electronic documents. Comparable to discography and bibliography, but not cartography.

We have been online since May 2000, and aim to be the best place to find and share science-related content of all kinds.

Share the love!

Please add more science to your life. Use our RSS feeds on your blog, your portal, or your favorite feedreader!

Powered by vBulletin® Version 3.7.2
Copyright ©2000 - 2008, Jelsoft Enterprises Ltd.
SEO by vBSEO 3.2.0 ©2008, Crawlability, Inc. Copyright © 2000-2008 Hypography
Part of the Hypography - Science for Everyone Network