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I have been trying to find out the bond angle of $\ce{H2O}$, but every site I visit has a different answer.

So far, I have found the following angles listed:

  • Site 1: 104.4º
  • Site 2: 107.5º OR 104.5º, depending on where you are in the article.
  • Site 3: 104.5º
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    $\begingroup$ Your second link does not say that water has a 107.5 degree bond angle. Rather, 104.5. $\endgroup$ – Dissenter Aug 27 '14 at 3:34
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    $\begingroup$ It actually says both... I suspect that 107.5 was a typo. $\endgroup$ – daviewales Aug 27 '14 at 4:14
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    $\begingroup$ First, there is no precise value due to Heisenberg uncertainty principle - there is only an average value. Second, under what conditions? The average bond angle will be different in liquid water at room temperature than in a vacuum at OK. $\endgroup$ – Jeff Aug 27 '14 at 23:07
  • $\begingroup$ Hmm... I guess I was looking for the average angle at standard temperature and pressure in liquid water. $\endgroup$ – daviewales Aug 28 '14 at 10:56
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In your comment, you say you are interested in "liquid water".

The values in your self-answer are for gas phase water, and the second source is citing the first source, so it is really just one source. The value is determined from gas phase rotation spectroscopy.

For liquid water, the value is not as precisely known:

105.5° (calculated) and 106° (experimental) as reported in Structural, electronic, and bonding properties of liquid water from first principles J. Chem. Phys. 111, 3572.

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While researching the above, I found some reliable sources that suggest the bond angle is 104.48º.

EDIT:

As DavePhD says, these values are for water in the gas phase. For liquid water, the bond angle is around 105.5-106º.

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  • $\begingroup$ Huh, I"ve never seen it written out to two decimal places. I guess this means that one of David Brin's books (which have a plot point involving 104 degrees) are technically correct and it would round down. $\endgroup$ – Canageek Aug 27 '14 at 6:46
  • $\begingroup$ Source 1 actually lists a theoretical value to three decimal places, but it lists the two decimal place version in the abstract. $\endgroup$ – daviewales Aug 28 '14 at 23:42

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