1. IIIIII Molecular Polarity Covalent Bonding

2. Covalent Bonds involve sharing electrons But Just like in real life, not all sharing Is equal !!!

3. / Electronegativity Electronegativity is the ability of an atom to Attract electrons to itself in a covalent bond Large ElectronegavitySmall Electronegativity

4. So, the atoms in a covalent bond are engaged in a tug-of-war over electrons electrons

5. Results of Tug of War

6. The atom that “wins” will be the one that is more electronegative. Because this atom gets the electrons more of the time, it becomes slightly negative The atom that “loses” becomes slightly positive

7. The Periodic Table allows us To predict differences in electronegavity F is the most electronegative

9. A. Dipole Moment n Means the direction of the polar bond in a molecule. n Arrow points toward the more electronegative atom. (The direction the electrons will flow H Cl ++ --

10. B. Determining Molecular Polarity n Depends on:  Electronegativity differences  dipole moments  molecular shape

11. B. Determining Molecular Polarity n Polar Molecules  Dipole moments are asymmetrical and don’t cancel. net dipole moment H2OH2O H H O

12. B. Determining Molecular Polarity n Nonpolar Molecules  Dipole moments are symmetrical and cancel out. BF 3 F F F B

13. CHCl 3 H Cl B. Determining Molecular Polarity n Therefore, polar molecules have...  asymmetrical shape (lone pairs) or  asymmetrical atoms net dipole moment

14. Example: CO2 Example: HCN Linear molecules can be nonpolar... Or Nonpolar. What makes the difference? No Net Dipole Moment Net Dipole Moment Towards N

15. Trigonal Planar molecules are usually nonpolar But, what makes this one polar? Example: BF3 Example: BF2Cl

16. Trigonal Pyramidal Molecules are Polar. Example: NH3 Net Dipole Toward N

17. Tetrahedral Molecules can be polar Or non polar Example: CH3F Example: CF4 Explain this!

18. Can a Molecule be Both Polar and NonPolar? Non Polar End Polar End Tetrahedral with symmetric atoms Trigonal planar with Asymmetric atoms

19. So, polarity can be more of a spectrum spectrum than a black and white determination Polar------------------------------------------------------nonpolar

20. More Nonpolar Molecules Share electrons the “best” Have the closest electronegativities (or smallest differences) Have lower boiling and melting points...so More likely to be gases at room temperature Like dissolves like... Use a nonpolar solvent to dissolve a nonpolar solute

21. More Polar Molecules Do not share well at all! Their electronegativity differences are great Are more like ionic compounds Have higher melting and boiling points Most likely to be liquids at room temperature Like dissolves like... Use a polar/ionic solvent to dissolve a polar/ionic solute

22. Ionic, Polar, Nonpolar: A Continuum Ionic------------ ------------Polar--------- -------Nonpolar Electrons transferred E- shared unequally E- shared Huge charge separation no charge sep. some charge sep. High mp/bp Low mp/bp Solids at STP Liquids at STP Gas at STP