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Polar Molecules H F electron rich region electron poor region  

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Presentation on theme: "Polar Molecules H F electron rich region electron poor region  "— Presentation transcript:

1 Polar Molecules H F electron rich region electron poor region  

2 Dipole moment (µ)? - A measure of molecular polarity - A polar molecule has µ ≠ 0 Non-polar molecule has µ = 0  = q x r q = charge (coulomb) r = the distance between charges (m)

3 The direction of polarity of a polar bond can be symbolised by a vector quantity ( ) The crossed end of the arrow is the positive end and the arrow head is the negative end. H  Cl

4 Example:

5 Covalent bond between same atoms  Covalent bond between atoms of the same element is nonpolar → nonpolar molecule.  Bonding electrons are shared equally. Example:

6 Covalent bond between different atoms  Covalent bond between different atoms is polar. - bonding electrons closer to the more electronegative atom.  However, molecules could be polar or nonpolar, depending on its shape.

7 Determining polar and nonpolar molecules Use the three-step approach outlined below :  Use electronegativity values to predict bond dipoles.  Use the VSEPR method to predict the molecular shape.  From the molecular shape, determine whether bond dipoles cancel to give a non- polar molecule or combine to produce a (resultant dipole moment) for the molecule.

8 Example: Molecules with different atoms & asymmetrically arranged are polar.

9 Molecules with different atoms, symmetrically arranged but having µ = 0 are nonpolar. In CCl 4, each bond is polar. The molecule as a whole, however, is nonpolar Example:

10 In SF 6, each bond is polar. The molecule is nonpolar

11 The molecule is polar because µ ≠ 0. The dipole moment arises because the difference in electronegativity. Example: Molecules with different atoms, symmetrically arranged but having µ ≠ 0 are polar.

12 Chloromethane ( CH 3 Cl) H H Cl C H The molecule is polar because µ ≠ 0. The dipole moment arises because the difference in electronegativity. Example:

13 Molecules with lone pairs on the central atom Note: Molecules which have lone pairs are usually polar. Let us consider the molecules in which there are lone pairs on the central atoms.

14 Ammonia ( effect of lone pairs )    0 Example:

15

16 O Which of the following molecules have a dipole moment? H 2 O, CO 2, SO 2, and CH 4 H H dipole moment polar molecule S O O CO O no dipole moment nonpolar molecule dipole moment polar molecule C H H HH no dipole moment nonpolar molecule

17 Indicate the direction in which the shared electron pair is shifted in the molecules given below. Exercise 1

18 Answer:

19 Exercise 2 Predicting the polarity of molecules. State which of them are polar and which are nonpolar. a) H 2 O b) NH 3 c) CCl 4 d) CHCl 3

20 Answer:


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