Linus pauling developed an arbitrary scale of

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Linus Pauling developed an arbitrary scale of electronegativities ( ) with values ranging from: F: =4.0 (most electronegative) to Fr: =0.8 (least electronegative)
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Slide 29 Electronegativity Increases Increases
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Bond Polarity and Partial Ionic Character Slide 30 When two atoms of differing electronegativities form a bond, the bonding pair of electrons is shared unequally; there is a higher electron density in the region of the more electronegative atom. Consider the bond formed when H( =2.1) combines with F( = 4.0) . Electron Density Distributions Note the much higher electron density around the F atom. The fractional ionic character in a bond is directly correlated with the electronegativity difference (  ).
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Bond Polarity and Partial Ionic Character Slide 31 The fractional ionic character in a bond is directly correlated with the electronegativity difference (  ). A rough “rule of thumb” is that bonds with  > 2 are basically ionic. However, this is still an approximation. Note that there is still a small amount of electron overlap in a “completely ionic” compound such as LiF (  = 3.0)
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Slide 32 Bond Polarity and Electronegativity Which of the following bonds are the (a) most polar, and (b) least polar. In each case, indicate the positive and negative ends of the bond. Atom F 4.0 O 3.5 N 3.0 C 2.5 H 2.1 Li 1.0 C-O N-C C-H Li-F  =3.5-2.5 =1.0  =3.0-2.5 =0.5  =2.5-2.1 =0.4  =4.0-1.0 =3.0 + - - + - + + - Most Polar (Ionic) Least Polar
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Slide 33 Bond Polarity and Electronegativity Without using a table of atom electronegativities, determine: Ga-Br As-Br Ga-Cl As-Cl Least Polar Which of the bonds below is the most polar? Which of the bonds below is the least polar? Most Polar
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Slide 34 Polar Bonds and Dipole Moments In physics, a positive and negative charge separated by a distance has a “dipole moment” ( ) Since a polar diatomic molecule has a separated positive and negative charge, it has a dipole moment. + - H-Cl  =3.0-2.1 =0.9 + - H-F  =4.0-2.1 =1.9 Because HF has a more polar bond than HCl, it has a larger dipole moment. Alternative Notation H-Cl H-F
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