Presentation on theme: "Polar Molecules H F electron rich region electron poor region "— Presentation transcript:
Polar Molecules H F electron rich region electron poor region
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)
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
Covalent bond between same atoms Covalent bond between atoms of the same element is nonpolar → nonpolar molecule. Bonding electrons are shared equally. Example:
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.
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.
Example: Molecules with different atoms & asymmetrically arranged are polar.
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:
In SF 6, each bond is polar. The molecule is nonpolar
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.
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:
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.
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
Indicate the direction in which the shared electron pair is shifted in the molecules given below. Exercise 1
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