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 Molecule Are 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