1. Chapter 7-2
Covalent Bonding

2. Covalent Bonds Electrons are shared between two atoms
Atoms with covalent bonds are called molecules
Anything made of molecules is a molecular substance
These can be made of 2 atoms or a million

3. Molecular / Structural Formulas
Molecular Formula: Tells how many atoms are in a molecule
Different compounds can have the same empirical formula and even the same molecular formula
Structural formula: Shows the bonds, one example is the Lewis Structure

4. Draw the Ammonia Molecule Are the valences satisfied?

5. Ammonia Molecule The lines represent shared pairs of electrons
The dots represent an unshared pair that are located in the valence of Nitrogen

6. Multiple Bonds Single bond = 2 shared electrons (one pair)
Double bonds= 4 shared electrons (two pair)
Formaldehyde
Triple bonds= 6 shared electrons (three pair)
Ethyne or Acetylene

7. Exceptions to the Octet Rule
Boron compounds contain less than 8 valence electrons
Example: Boron trifluoride

8. Exceptions to the Octet Rule
Beyond the second row have more than 8 valence electrons due to the d orbitals.
Examples: phosphorus and sulfur

9. Exceptions to the Octet Rule
Odd number molecules
Example Nitrogen monoxide

10. Properties of Covalent Molecules
Most bonds will not share the electrons equally
Electrons are closer to the more electronegative atom
Page 241 gives electronegativities of representative elements

11. Properties of Covalent Molecules
When one atom is significantly more electronegative than another, the molecule is polar
Similar electronegativities result in non-polar molecules

12. Predicting
If you know the electronegativities of the atoms you can predict the molecules polarity
Difference 0.4 or less= Non-polar
Difference of 2.0 or greater = Very polar or ionic

13. Bond Type By Electronegativity
Electronegativity Difference
Bond Type
< Or = to 0.4
Non-polar Covalent
Between and 2.0
Polar Covalent
> Or = to 2.0
Ionic