What is a Polar Covalent Bond?

A polar covalent bond is a bond between two non-metals with different electronegativities. Only bonds between the same elements are truly nonpolar. The higher the difference in electronegativity, the more polar the bond is. Take a look at this table of electronegavities and let's try some examples.  

http://www.tutor-homework.com/Chemistry_Help/electronegativity_table/electronegativity.html

consider the following bonds. They are arranged in order of increasing polarity:

Cl-Cl
H-C
H-Cl
H-O
H-F

We calculate the difference in electonegativity for each. I will use the absolute value because the sign is not important. The more electronegative atom is the negative side of the bond.

Cl-Cl  2.55 - 2.55 = 0 it's not polar at all.

H-C   2.1 - 2.55 =  0.45 it's barely polar

H-Cl  2.1 - 3.16  = 1.06 more polar

H-O   2.1 - 3.44  = 1.34 more polar again

H-F  2.1 - 3.98 = 1.88 more polar than the rest

If an electron pair is 50/50 shared between two atoms, then the bond is non-polar, and covalent.  If the electron pair moves a bit towards the more electronegative atom of the pair, it becomes polar covalent.  If the pair moves completely to one end (big electronegativity difference) the bond is called ionic.

Dear Just Wondering,

 A good example of a Covalent Bond is that formed between a diatomic molecule or a metal to non-metal bond for an example. F^-1 + F^+1 --------> F2,  Zn^+2 + O^-2 ---------> ZnO. Covalent Bond - Electron sharing bond.

 A few good examples of a Polar Covalent Bond would be that of the molecules of water H2O and CO3. Polar Covalent Bonds have dipoles which form positive dipoles on the hydrogen atoms and carbon atoms, and negative dipoles on the oxygen atoms of the molecules.


For additional information, please see also:

http://en.wikipedia.org/wiki/Ionic_bonds
http://en.wikipedia.org/wiki/Covalent_bonds
http://en.wikipedia.org/wiki/Polar_bonds
http://en.wikipedia.org/wiki/Diatomic_molecule
http://en.wikipedia.org/wiki/Water_(molecule)
http://en.wikipedia.org/wiki/Zinc_oxide
http://en.wikipedia.org/wiki/Carbon_trioxide
http://en.wikipedia.org/wiki/Dipole_moment
http://en.wikipedia.org/wiki/Dipole
http://en.wikipedia.org/wiki/Electron_electric_dipole_moment
http://en.wikipedia.org/wiki/Bond_dipole_moment
http://en.wikipedia.org/wiki/Magnetic_dipole_moment
http://www.vias.org/genchem/physprop_12595_03.html
http://en.wikipedia.org/wiki/Electronegativity
http://en.wikipedia.org/wiki/Elementary_charge

http://environmentalchemistry.com/yogi/periodic/electronegativity.html

http://www.chemguide.co.uk/atoms/bonding/electroneg.html

http://www.lenntech.com/periodic-chart-elements/electronegativity.htm



http://hyperphysics.phy-astr.gsu.edu/hbase/electric/diph2o.html

http://www.chemistry.mcmaster.ca/esam/Chapter_7/section_1.html

http://www.chemistry.mcmaster.ca/esam/Chapter_7/section_3.html

http://www.chemistry.mcmaster.ca/esam/Chapter_7/section_4.html





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