POLAR COVALENT COMPOUNDS

Introduction to Covalent Bonding:

Bonding between non-metals consists of two electrons shared between two atoms. Using the Wave Theory, the covalent bond involves an overlap of the electron clouds from each atom. The electrons are concentrated in the region between the two atoms. In covalent bonding, the two electrons shared by the atoms are attracted to the nucleus of both atoms. Neither atom completely loses or gains electrons as in ionic bonding.

There are two types of covalent bonding:

1. Non-polar bonding with an equal sharing of electrons.

2. Polar bonding with an unequal sharing of electrons. The number of shared electrons depends on the number of electrons needed to complete the octet.

POLAR BONDING results when two different non-metals unequally share electrons between them. One well known exception to the identical atom rule is the combination of carbon and hydrogen in all organic compounds.

The non-metal closer to fluorine in the Periodic Table has a greater tendency to keep its own electron and also draw away the other atom's electron. It is NOT completely successful. As a result only partial charges are established. One atom becomes partially positive since it has lost control of its electron some of the time. The other atom becomes partially negative since it gains electron some of the time.

Comparison of Ionic, Polar and Non-Polar Bonding

HYDROGEN CHLORIDE:

Hydrogen Chloride forms a polar covalent molecule. The graphic shows that chlorine has 7 electrons in the outer shell. Hydrogen has one electron in its outer energy shell. Since 8 electrons are needed for an octett, they share the electrons.

However, chlorine gets an unequal share of the two electrons, although the electrons are still shared (not transfered as in ionic bonding), the sharing is unequal. The electrons spends more of the time closer to chlorine. As a result, the chlorine acquires a "partial" negative charge. At the same time, since hydrogen loses the electron most - but not all of the time, it acquires a "partial" charge. The partial charge is denoted with a small Greek symbol for delta.

WATER:

Water, the most universal compound on all of the earth, has the property of being a polar molecule. As a result of this property, the physical and chemical properties of the comnpound are fairly unique.

Hydrogen Oxide or water forms a polar covalent molecule. The graphic shows that oxygen has 6 electrons in the outer shell. Hydrogen has one electron in its outer energy shell. Since 8 electrons are needed for an octet, they share the electrons.

However, oxygen gets an unequal share of the two electrons from both hydrogen atoms. Again, the electrons are still shared (not transfered as in ionic bonding), the sharing is unequal. The electrons spends more of the time closer to oxygen. As a result, the oxygen acquires a "partial" negative charge. At the same time, since hydrogen loses the electron most - but not all of the time, it acquires a "partial" charge. The partial charge is denoted with a small Greek symbol for delta.

Octet Rule: Elemental atoms generally lose, gain, or share electrons with other atoms
in order to achieve the same electron structure as the nearest rare gas with eight
electrons in the outer level.

The proper application of the Octet Rule provides valuable assistance in predicting and explaining various aspects of chemical formulas.