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Bonding
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Regions of Electron Density
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<font size="4" face="Verdana, Arial, Helvetica, sans-serif">Regions of
electron density include single, double, and triple bonds, and unshared
pairs of electrons.</font>
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org.concord.modeler.text.LineIcon750.03010515<html><body align="center"><strong><font size="5" face="Verdana, Arial, Helvetica, sans-serif" color="rgb(051, 051, 051)">Covalent Bonds are Regions of Electron Density</font></strong></body></html>-458704
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<font face="Verdana, Arial, Helvetica, sans-serif" size="4">In molecular
hydrogen (H<sub>2</sub>, shown at right) each hydrogen atom contributes
one electon to a single bond between two atoms. <b>This bond, like any
covalent bond, is one region of electron density.</b> The electrons are
found in an area betweeen and around the atoms that are bonded. Here are
some different ways of showing the electrons that form covalent bonds.</font>
<p>
<b><font size="4" face="Verdana, Arial, Helvetica, sans-serif">Bond
diagrams </font></b><font size="4" face="Verdana, Arial, Helvetica, sans-serif">use
lines for each shared pair. </font>
</p>
<p>
<b><font size="4" face="Verdana, Arial, Helvetica, sans-serif">Lewis dot
structures</font></b><font size="4" face="Verdana, Arial, Helvetica, sans-serif">
show unshared (non-bonding) electrons as well as shared electrons.</font>
</p>
<p>
<font size="4" face="Verdana, Arial, Helvetica, sans-serif">An<b>
"orbital view"</b> shows a hazy blue area where you are most
likely to find shared electrons. </font>
</p>
<p>
<font size="4" face="Verdana, Arial, Helvetica, sans-serif">In the <b>"ball
and stick plus" view</b> a 'stick' bond shows us how the atoms are
connected and a region of electron density is also shown.</font>
</p>
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<img src="rep-multbonds.jpg">
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<b><font size="5" face="Verdana, Arial, Helvetica, sans-serif">Multiple
bonds also count as one region of electron density</font></b><font size="5" face="Verdana, Arial, Helvetica, sans-serif">
</font>
<p>
<font size="4" face="Verdana, Arial, Helvetica, sans-serif">Each double
bond in carbon dioxide (CO<sub>2</sub>, at left) is counted as one area
of electron density. As a result, <b>CO<sub>2</sub> has only two regions
of electron density, even though it is sharing a total of four pairs of
electrons.</b></font>
</p>
<p>
<font size="4" face="Verdana, Arial, Helvetica, sans-serif">Although we
don't show it here, the same is true of triple bonds. A triple bond
counts as <b>one</b> region of electron density.</font>
</p>
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org.concord.modeler.text.LineIcon750.03010515<html><body align="center"><strong><font size="5" face="Verdana, Arial, Helvetica, sans-serif" color="rgb(051, 051, 051)">Any Unshared Electron Pair is a Region of Electron Density </font></strong></body></html>-458704
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<b><font size="5" face="Verdana, Arial, Helvetica, sans-serif">Unshared
electrons</font></b><font size="5" face="Verdana, Arial, Helvetica, sans-serif">
</font>
<p>
<font size="4" face="Verdana, Arial, Helvetica, sans-serif">Ammonia (NH<sub>3</sub>,
shown at right) is a molecule with one unshared pair of electrons in
addition to three shared pairs. The unshared pair is important. It
occupies an orbital, is repulsed by the shared electrons, and repulses
them as well. <b>So NH<sub>3</sub> has a total of four regions of
electron density. </b></font>
</p>
<p>
</p>
<div align="center">
<table with="95%" border="1">
<tr>
<td>
<p>
<b><font size="4" face="Verdana, Arial, Helvetica, sans-serif">Your
task:</font></b>
</p>
<ul>
<li>
<b><font size="4" face="Verdana, Arial, Helvetica, sans-serif">Right
click on the image to the right and select "Annotate". </font></b>
</li>
<li>
<b><font size="4" face="Verdana, Arial, Helvetica, sans-serif">Choose
any ONE of the NH3 structures shown in the snapshot and use
the "draw a rectangle" button <img src="drawrect.png">
to draw boxes around the four regions of electron density.</font></b><font size="4" face="Verdana, Arial, Helvetica, sans-serif">
</font>
</li>
</ul>
</td>
</tr>
</table>
</div>
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