Chapter 7-2

Covalent Bonding

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

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

Draw the Ammonia MoleculeAre the valences satisfied?

Ammonia Molecule

• The lines represent shared pairs of electrons

• The dots represent an unshared pair that are located in the valence of Nitrogen

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

Exceptions to the Octet Rule

• Boron compounds contain less than 8 valence electrons– Example: Boron

trifluoride

Exceptions to the Octet Rule

• Beyond the second row have more than 8 valence electrons due to the d orbitals.– Examples: phosphorus

and sulfur

Exceptions to the Octet Rule

• Odd number molecules– Example Nitrogen

monoxide

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

Properties of Covalent Molecules

• When one atom is significantly more electronegative than another, the molecule is polar

• Similar electronegativities result in non-polar molecules

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

Bond Type By Electronegativity

Electronegativity Difference Bond Type

< Or = to 0.4 Non-polar Covalent

Between 0.4 and 2.0 Polar Covalent

> Or = to 2.0 Ionic