1. Bond polarity vs. Molecule polarity

2. Bond polarity
Unless the two atoms involved are the same (like in H2 or Cl2), covalent bonds tend to be polar.
This means that one atom is pulling more strongly on the shared pair of electrons than the other.
Most covalent bonds involve an uneven sharing of electrons.

3. Electronegativity
Electronegativity is a relative measure of how strongly an element pulls on the shared pair of electrons in a covalent bond.
Highest EN – Fluorine (top right)
Lowest EN – Francium (bottom left)

4. Electronegativity Why does fluorine have the highest EN?
Compared to other elements in its column, the shared pair of electrons are closer to the nucleus because they are in a lower energy level. Closer to the nucleus = stronger pull from the protons.
Compared to other elements in its row (all of which have valence electrons in the 2nd energy level), fluorine has more protons. The protons attract the electron pair.

5. Electronegativity
The element with the highest EN (fluorine) is in the top right of the table. How come He and Ne aren’t included?

6. When showing polar bonds, the arrow points toward the more EN atom.
H Cl + -

7. Molecular Polarity
Whether or not it contains polar covalent bonds, the polarity of a molecule depends on its shape.
Molecules that are perfectly symmetric around the central atom will be nonpolar.
Molecules that are asymmetric will be polar.

8. Molecular Polarity BF3 Nonpolar Molecules
Outer atoms are arranged symmetrically around the central atom.
Pulls of the polar bonds cancel out.
BF3 F B

9. Molecular Polarity H2O net polarity Polar Molecules
Outer atoms are arranged asymmetrically around the central atom.
Pulls of the polar bonds do not cancel out.
The molecule has a permanent polarity.
H2O H O
net
polarity

10. Which geometries result in nonpolar molecules?
The symmetric ones!
Linear (sp)
Trigonal planar (sp2)
Tetrahedral (sp3)
Trigonal bipyramidal, linear (sp3d)
Octahedral, square planar (sp3d2)

11. Which geometries result in polar molecules?
The asymmetric ones!
Bent (sp2)
Trigonal pyramidal, bent (sp3)
See-saw, t-shaped (sp3d)
Square pyramidal (sp3d2)