A concept invented by Linus Pauling to measure the tendency for atoms to form ionic instead of covalent bonds.The electronegativity is denoted , and the electronegativity difference between compounds A and B is defined by

where

The absolute scale of electronegativity is set by fluorine, which is assigned an electronegativity of . In a simple molecule, the atom with the lowest electronegativity is likely to be the central one.
<TABLE CELLPADDING=3 BORDER="1"> <TR><TD ALIGN="LEFT"> <IMG WIDTH="40" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" SRC="http://scienceworld.wolfram.com/chemistry/eimg7.gif"></TD> <TD ALIGN="LEFT">type of bonding</TD> </TR> <TR><TD ALIGN="LEFT">0.0</TD> <TD ALIGN="LEFT">pure covalent bond (equal sharing of <IMG WIDTH="22" HEIGHT="17" ALIGN="BOTTOM" BORDER="0" SRC="http://scienceworld.wolfram.com/chemistry/eimg8.gif">s)</TD> </TR> <TR><TD ALIGN="LEFT">0.1-0.4</TD> <TD ALIGN="LEFT">nonpolar covalent bond (almost equal attraction for shared <IMG WIDTH="22" HEIGHT="17" ALIGN="BOTTOM" BORDER="0" SRC="http://scienceworld.wolfram.com/chemistry/eimg8.gif"> pairs)</TD> </TR> <TR><TD ALIGN="LEFT">0.5-1.4</TD> <TD ALIGN="LEFT">polar covalent bond (unequal sharing of <IMG WIDTH="22" HEIGHT="17" ALIGN="BOTTOM" BORDER="0" SRC="http://scienceworld.wolfram.com/chemistry/eimg8.gif">s)</TD> </TR> <TR><TD ALIGN="LEFT">1.5-3.2</TD> <TD ALIGN="LEFT">ionic bond (<IMG WIDTH="22" HEIGHT="17" ALIGN="BOTTOM" BORDER="0" SRC="http://scienceworld.wolfram.com/chemistry/eimg8.gif"> transfer)</TD> </TR> </TABLE>
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