1. Covalent Bonding
Molecular Polarity

2. Shape and Geometry Review

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

4. Electronegativity is the ability of an atom to
Attract electrons to itself in a covalent bond
Large Electronegavity
Small Electronegativity

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

6. Results of Tug of War

7. 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

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

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

11. B. Determining Molecular Polarity
Depends on:
Electronegativity differences
dipole moments
molecular shape

12. B. Determining Molecular Polarity
Polar Molecules
Dipole moments are asymmetrical or have lone pairs,and don’t cancel .
H2O H O
net
dipole
moment

13. B. Determining Molecular Polarity
Nonpolar Molecules
Dipole moments are symmetrical and cancel out.
BF3 F B

14. B. Determining Molecular Polarity
Therefore, polar molecules have...
asymmetrical shape (lone pairs) or
asymmetrical atoms
CHCl3 H Cl
net
dipole
moment

15. Linear molecules can be nonpolar . . .
Example: CO2
What makes
the difference?
No Net Dipole Moment
Or Polar…
Example: HCN
Net Dipole Moment Towards N
N has a pair of unshared electrons here

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

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

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

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

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

21. Ionic, Polar, Nonpolar: A Continuum
Electrons transferred E- shared unequally E- shared
Huge charge separation no charge sep.
some charge separation
High MP/BP Low MP/BP
Solids at STP Liquids at STP Gas at STP
STP is Standard Temperature and Pressure (273 K and 1 atm)

22. 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

23. 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