Polar Molecules electron poor region electron rich region

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Polar Molecules electron poor region electron rich region H F d+ d-

Polar Molecules electron poor region electron rich region H F d+ d-

Dipole moment (µ)? - A measure of molecular polarity m=qxr q = charge (coulomb)

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

• The direction of polarity of a polar bond can be symbolised by

• 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

Example:

Example:

Covalent bond between same atoms Ø Covalent bond between atoms of the same element

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

Covalent bond between different atoms Ø Covalent bond between different atoms is polar. -

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

Determining polar and nonpolar molecules Use three-step approach outlined below : Ø Use electronegativity

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

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

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

Molecules with different atoms, symmetrically arranged but having µ = 0 are nonpolar. Example:

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

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

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

Molecules with different atoms, symmetrically arranged but having µ ≠ 0 are polar. Example:

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

Example: Chloromethane ( CH 3 Cl) Cl C H H H The molecule is

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

Molecules with lone pairs on the central atom Let us consider the molecules in

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

Example: Ammonia ( effect of lone pairs ) 0

Example: Ammonia ( effect of lone pairs ) 0

Which of the following molecules have a dipole moment? H 2 O, CO 2,

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

Exercise 1 Indicate the direction in which the shared electron pair is shifted in

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

Answer:

Answer:

Exercise 2 Predicting the polarity of molecules. State which of them are polar and

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

Answer:

Answer:

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