UTF-8Molecular dipoles rotate and align: The case of water255255192
Molecular dipoles are permanent
All atoms in a molecule are engaged in an atomic tug-of-war. Each attracts the cloud toward itself. The strongest wins shifting the electron cloud of the entire molecule toward itself, creating somewhere a lack of electrons. Polar molecules have electron-rich regions, or a negative pole and a positive pole. This is a molecular dipole. Some molecules make quite strong permanent dipoles.
The case of water
Water is a permanent dipole. See how three water dipoles are aligned so a "minus" of one is aligned with the positive pole of another dipole. The resulting structures are strong -- try to compress water! How do dipoles "know" which way to rotate?
In the case of water, oxygen is always a winner in the tug-of-war for electrons. Both hydrogen atoms are electron-poor. The electrons pair O-H bonds are supposed to share are shifted toward the oxygen atom.
Water is a strong permanent dipole. One negative pole is around the oxygen atom and the positive pole is where the hydrogen atoms are. Look at the model below. What happens if you have tie a bunch of dipoles like water molecules together? Remove some heat and see what happens.
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<b><font size="5" face="Trebuchet MS">Molecular dipoles rotate and align: The Case of Water</font></b>
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<font size="4">Observe one dipole. See how it rotates to align with the
other dipoles. Press the <img src="play.gif"> button to run the
simulation. </font>
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<font size="4">Experiment with the controls below. Then <strong>take a
snapshot of the model and annotate your image so that you indicate where
you observed at least one hydrogen bond</strong> in the model. </font>
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<font size="4"><input name="Submit" value="Heat" script="script:mw:1:select atom all; heat 0.1; select atom none;" type="submit">
<input name="Submit2" value="Cool" script="script:mw:1:select atom all; heat -0.1; select atom none;" type="submit">
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