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Covalent Bonding:

Objectives:

    1.    Describe the characteristics of a covalent bond.

    2.    Describe the difference between polar and nonpolar covalent bonds.

Key Terms:

    molecule    molecular substance    molecular formula    structural formula    Lewis structure    unshared pair    single covalent bond    double covalent bond    triple covalent bond    polar    nonpolar

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Notes:

Though we have learned about the forming of bonds through the transfer of electrons, the majority of compounds that we come in contact with in our daily lives are formed in a completely different manner.  The atoms are covalently bonded.  A covalent bond is one where the electrons are shared.  A group of covalently bonded atoms is called a molecule.  These molecular substances include DNA, sugar and carbon dioxide.  The molecules can contain as few as 2 atoms and as many as a million.  Rules for covalent bonds:
electrons are shared in covalent molecules
covalently bonded molecules follow the octet rule (some exceptions - BF3)
covalent molecules can form single, double, or triple bonds
covalent bonds can be rearranged to form different molecules (glucose, fructose, & maltose)

Most covalent bonds are slightly polar in nature.  What this means is that electrons are not evenly shared between the atoms.  This is due to the different electronegativity (electron attracting) values of the individual atoms.  Lets look at water (H20):

electronegativity of H = 2.1
electronegativity of O = 3.5

The resulting molecule is considered polar where oxygen becomes slightly negative and the hydrogen becomes slightly positive.

Molecules can also be non polar.  The non polar molecule is electrically neutral and stable.   Examples include O2, N2 and F2  You can use the following chart to predict the type of bond.

Electronegativity Difference Bond Type
< 0.4 nonpolar covalent
between 0.5 and 1.9 polar covalent
> 2.0 ionic

 

Formulas:

Empirical

lists atom ratios in the ratios that are present in the molecules
not good for describing covalently bonded molecules
        CH2O is wood, sugar, lactic acid, etc ...

Molecular:

lists the atoms in the found in the molecule without reducing
better that the empirical formula but not the best for describing molecules
        C6H12O6 - fructose, C6H12O6 - glucose, C6H12O6 - galactose

Structural:

shows where the individual atoms are bonded
Lewis structures are an example of this type of formula
        Dashes are a shorthand way of showing bonds
Diagram of glucose

Diagram of fructose

(www.cherrybyte.org/Articles/ bugbytes/sugar/fructose.gif)

 

 

 

 

 

 

 

 

Last modified: November 08, 2002