1. Chemistry Notes Polarity of Molecules

2. Polarity What creates polarity in a molecule? Migration of bond electrons –Recall we determine the direction of this movement with electronegativity Bond e- move toward the atom with a higher electonegativity Dipole Moments: a quantitative measure of polarity of a bond

3. Polarity Consider the Lewis structure for hydrofluoric acid: HF Fluorine is more electronegative than hydrogen Electrons shift from H to F The shift is symbolized by a cross arrow ( ) The consequent charge is represented as –δ+ - Represents a partial positive charge –δ- - Represents a partial negative charge

4. Polarity Molecules that have partial charges are referred to as polar molecules. –Ionic compounds are also polar molecules Molecules that do not have dipole moments are called non-polar molecules. –Remember dipole moments create the partial charge

5. Polar Molecules

6. Nonpolar Molecule

7. Polarity Determining Polarity If all bonds are non- polar, the molecule is non-polar If at least one bond is polar, the molecule is polar, UNLESS it is symmetrical, then it is non-polar

8. Consider the molecule NH 3 N is more electro-negative than H Electrons move closer to N Unshared electrons on N also have a dipole moment (up) NH 3 has an overall polarity upwards

9. Consider the molecule NF 3 N is less electro- negative than F Electrons move closer to F Unshared electrons on N also have a dipole moment (up) NF 3 has an overall polarity downwards

10. Polar v. Nonpolar

12. Summary Be able to… Explain what creates polarity Determine a dipole –Using the cross-arrow –Assign partial charges Tell whether a molecule is polar or nonpolar