COVALENT: Polar AND Non-Polar

COVALENT: Polar AND Non-Polar

History

            In 1704, Isaac Newton famously outlined his atomic bonding theory, in "Query 31" of his Opticks, whereby atoms attach to each other by some "force". Specifically, after acknowledging the various popular theories in vogue at the time, of how atoms were reasoned to attach to each other, i.e. "hooked atoms", "glued together by rest", or "stuck together by conspiring motions", Newton states that he would rather infer from their cohesion, that "particles attract one another by some force, which in immediate contact is exceedingly strong, at small distances performs the chemical operations, and reaches not far from the particles with any sensible effect."

           In 1819, Jöns Jakob Berzelius developed a theory of chemical combination stressing the electronegative and electropositive character of the combining atoms. Mid-19th century, Edward Frankland, F.A. Kekule, A.S. Couper, A.M. Butlerov, and Hermann Kolbe, building on the theory of radicals, developed the theory of valency, originally called "combining power", in which compounds were joined owing to an attraction of positive and negative poles. In 1916, chemist Gilbert N. Lewis developed the concept of the electron-pair bond, in which two atoms may share one to six electrons, thus forming the single electron bond, a single bond, a double bond, or a triple bond; in Lewis's own words, "An electron may form a part of the shell of two different atoms and cannot be said to belong to either one exclusively."

Polar Covalent Bond

The above figure is an illustrative representation of a water molecule having polar covalent bonds between the Oxygen atom and the Hydrogen atoms.

In a polar covalent bond, the electrons shared by the atoms spend a greater amount of time, on the average, closer to the Oxygen nucleus than the Hydrogen nucleus. This is because of the geometry of the molecule and the great electron negativity difference between the Hydrogen atom and the Oxygen atom. 

The result of this pattern of unequal electron association is a charge separation in the molecule, where one part of the molecule, the Oxygen, has a partial negative charge and the Hydrogen have a partial positive charge. 

A polar bond is formed when electrons are unequally shared between two atoms. Polar covalent bonding occurs because one atom has a stronger affinity for electrons than the other. The bonding electrons will spend a greater amount of time around the atom that has the stronger affinity for electrons.

Non Polar Covalent Bond

The H₂ molecule is a good example of the first type of covalent bond, the non polar bond. Because both atoms in the H₂ molecule have an equal attraction or affinity for electrons, the bonding electrons are equally shared by the two atoms and whenever two atoms of the same element bond together, a non polar bond is formed.

Non-Polar bonding results when two identical non-metals equally share electrons between them. One well known exception to the identical atom rule is the combination of carbon and hydrogen in all organic compounds.

References:

http://academic.brooklyn.cuny.edu/biology/bio4fv/page/nonpola.htm

http://www.visionlearning.com/library/module_viewer.php?mid=55

http://www.elmhurst.edu/~chm/vchembook/150npcovalent.html

http://academic.brooklyn.cuny.edu/biology/bio4fv/page/polar_c.htm

Members:

 Group 1

Dianne Ang

Androse Ansaldo

Micah Antonio

Oya Bautista

Angela Cansana