1. Molecular Compounds
Polarity

2. Molecular Compounds
Polarity – is the difference between the electronegativity values for the two atoms sharing a pair of electrons.
The greater the difference, the more polar the bond is.

3. Molecular Compounds
Nonpolar Covalent Bonds – this occurs when the two atoms sharing the electrons have the same electronegativity.
H Cl Br N2
The electron pair is shared equally between the two atoms.

4. Molecular Compounds
Polar Bonds - this occurs when the two atoms sharing the electrons have different electronegativity values.
H-C N-O C-Cl
The electron pair is shared unequally between the two atoms.
This unequal sharing is shown by drawing an arrow towards the more electronegative atom

5. Molecular Compounds Examples: C O C Cl
d d d d-
C O C Cl
d+ is a partial positive charge caused by the e- moving away from the atom
d- is a partial negative charge caused by the e- moving toward the atom

6. Molecular Compounds
A molecule can have polar bonds, yet still not be a polar molecule.
You must evaluate the bonds as they appear in the 3-D shape of the molecule.

7. Molecular Compounds Example: CO2 O=C=O AX2 linear 180o
Therefore, the pull of one bond cancels out the pull of the other bond. (tug-of-war; the middle doesn’t move)
Each bond is polar, but the overall affect results in a nonpolar molecule

8. Molecular Compounds Example: CH4 AX4 tetrahedral 109.5o
H C H
AX4 tetrahedral o
Again, each bond is polar, yet overall, the effects cancel each other out.
The molecule is nonpolar

9. Molecular Compounds Example: NH3 H ;; H - N - H
AX3E trigonal pyramidal o
Each bond is polar. In this case, the molecule is polar As the electrons are being drawn towards one end of the molecule. d- d+

10. Molecular Compounds
It is the uneven distribution of electrons in a molecule that results in a dipole moment.
Example:
Compare the dipole moment in H2S to that of H2O

11. Molecular Compounds H2S AX2E2 bent 109.5 H2O AX2E2 bent 109.5
Because the H-S bond is less polar than the H-O bond, the dipole moment in H2S is weaker than the dipole moment in H2O