Water O-H Bond Length: Evidence & Measurement

In summary, the website you referenced suggests that there are not 0.942 H-O bond lengths in liquid water.
  • #1
zincshow
104
0
Not sure where this goes, but here goes:

Water O-H bond is usually thought of as 0.942 angstrom when looked at as H2O molecules.

This very nice site on water http://www.lsbu.ac.uk/water/evidnc.html suggests that x-ray data O···H peaks at 1.85 Å and 3.3 Å with no peak less then 1.85, suggesting there are not 0.942 H-O bond lengths in liquid water. Does this sound correct?
 
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  • #2
Intramolecular H-O bond lengths are approximately 0.9 - 1.0 Angstroms in liquid water at 25 C; intermolecular (hydrogen) bond lengths are much longer, quite possibly around 1.8 Angstroms as your source claims. Of course, all that changes for various phases at different temperatures. Crystal formation in ice should lead to H-O bond length changes to accommodate for hexagonal crystal packing, for example.
 
  • #3
jthechemist said:
Intramolecular H-O bond lengths are approximately 0.9 - 1.0 Angstroms in liquid water at 25 C; intermolecular (hydrogen) bond lengths are much longer, quite possibly around 1.8 Angstroms as your source claims. Of course, all that changes for various phases at different temperatures. Crystal formation in ice should lead to H-O bond length changes to accommodate for hexagonal crystal packing, for example.

I agree, but from searching defraction data for liquid water it seems to agree with their statement:

"However the model gives H···H peaks at 2.35 Å, 3.9 Å and 4.6 Å with a small peak at 2.9 Å and O···H peaks at 1.85 Å and 3.3 Å with smaller peaks at 4.55 Å and 5.25 Å similar to published data [17, 35, 37]."

Which makes me wonder why do they not see any O...H peaks under 1 Angstrom? Why do people think there are "Intramolecular H-O bond lengths are approximately 0.9 - 1.0 Angstroms in liquid water at 25 C"?
 
  • #4
Radial distribution functions are useful for studying surrounding structure; the intramolecular OH bonds are *always* there and thus do not contribute any key insight. Thus the peaks arising from intramolecular bonds are often removed. See point (c) on the website you referenced: http://www1.lsbu.ac.uk/water/evidnc.html#c
 
  • #5
Thank you. My mistake.
 

1. What is the O-H bond length in water?

The O-H bond length in water is approximately 0.96 Angstroms (Å) or 96 picometers (pm). It is considered a short bond length due to the strong electronegativity of oxygen and the small size of the hydrogen atom.

2. How is the O-H bond length in water measured?

The O-H bond length in water is typically measured using spectroscopic techniques such as infrared or Raman spectroscopy. These methods involve shining light on a water sample and measuring the wavelengths of light absorbed or scattered by the O-H bond. The resulting spectra can be used to determine the bond length.

3. Why is it important to measure the O-H bond length in water?

The O-H bond length in water is important because it affects the physical and chemical properties of water. For example, the short bond length contributes to water's high boiling point and surface tension. It also plays a role in the ability of water to form hydrogen bonds and interact with other molecules.

4. How does the O-H bond length in water change with temperature?

The O-H bond length in water is known to increase slightly with increasing temperature. This is due to thermal expansion, where the molecules vibrate more at higher temperatures and the bonds become slightly longer. However, this change is very small and has minimal impact on the overall properties of water.

5. Is the O-H bond length in water constant?

No, the O-H bond length in water is not constant. It can vary slightly depending on factors such as temperature and pressure. It can also be affected by the presence of other molecules or ions in the water, as they can interact with the hydrogen atoms and affect the bond length. However, these variations are very small and the O-H bond length in water is generally considered to be fairly consistent.

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