Meeting%2034%20F%202010

Meeting%2034%20F%202010 - Meeting 34, 35 Chapter 10 Polar...

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1 Meeting 34, ½ 35 – Chapter 10 Polar Molecules and Dipole Moments A molecule with separate centers of positive and negative charge is called a polar molecule The dipole moment ( m ) of a molecule is the product of the magnitude of the charge ( d ) and the distance ( d ) that separates the centers of positive and negative charge m = d d Dipole moments are measured in debye 1 debye (D) = 3.34 x10 -30 Cm Polar molecules such as HCl orient in an electric field. Nonpolar molecules such as Cl 2 do not. Q. How would NH 3 tend to orient in an electric field?
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2 No electric field Electric field How do we determine whether a molecule has a dipole moment? When there is an electronegativity difference between the atoms, the bond is polar. It has an electric dipole moment) A d + -B d -
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3 The vector sum of bond dipole moments in a molecule is the dipole moment of the molecule. Example : determine whether CO 2 is expected to be polar or nonpolar. Draw the Lewis structure and use VSEPR to determine the geometry and ΔEN to determine bond polarity. CO 2 has polar bonds, but the bond vectors cancel (think of two horses pulling a rope in opposite directions with equal force). The center of positive and of negative charge coincide at the C atom and CO 2 has no dipole moment.
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4 Example 2: water has polar bonds and a dipole moment. The bond dipoles do not cancel, the centers
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Meeting%2034%20F%202010 - Meeting 34, 35 Chapter 10 Polar...

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