What is Polarity Definition

Polarity is basically the difference in electronegativity between two molecules; which is simply the affinity of an atom to electrons. Atoms of the same molecule have influence on each other in many ways. One of the reasons is electronegativity. An example is a water molecule, because of the electronegativity difference between the Oxygen atom (3.4) and Hydrogen atom (2.2) it has areas of partial negative and positive charges. Meaning that one side of the bond possesses a partial negative charge, while the other side has a partial positive charge. This is referred to as polarity, and the water molecule is said to be polar. This polarity is due to the electronegativity of the atom-of-oxygen.

The example of the Oxygen – atom in the water – molecule explains polarity. Oxygen atoms attracts electrons more than the Hydrogen atoms. This results that the pair of electrons shared spend more time around the oxygen nucleus than around the hydrogen nucleus. When a shared electrons’ pair is orbiting the oxygen nucleus, the proton of the hydrogen nucleus is exposed and the oxygen/atom has more electrons than protons. This creates the partial -ve and partial +ve charges making the molecule of water acquire polarity characteristics.

Electronegativity of oxygen cause polarity in water-molecule

The relative electronegativities of the atoms involved is what determines the polarity of bonds determined. These electronegativity values are also determined from a variation of the periodic table of the elements called the periodic table of elements.

Most hydrocarbons (molecules made up of both Carbon and Hydrogen atoms) are extremely nonpolar because of the similarity in the electronegativity of Carbon – Hydrogen. In other words, the hydrogen and carbon atoms share electrons fairly equally.

Polarity caused by electronegativity difference between two atoms in molecule 

Polarity and properties of molecules

Nonpolar molecules do not have significant partial charges, therefore they will not attract polar molecules. Opposite charges attract, similar charges repel one another, but there is no attraction or repulsion between nonpolar molecules. For example, we know that gasoline (a hydrocarbon) will not mix with water. However, if we add oxygen to the hydrocarbon molecules we see that the molecules become polar. Ethanol (drinking alcohol), for instance, completely mixes with water.

Soaps and detergents are unique molecular combinations of polar and nonpolar compounds. Nonpolar part of molecule will react with oils found on soiled hands or clothing while polar part reacts with water. The result is oils removal (nonpolar) from water (high polarity). The polar end of soap is a functional group.

soap made of hydrocarbons and polar end functional group

The incompatibility between nonpolar compounds and water is due to the attraction that water molecules exhibit for one another. Positive charge on the hydrogen of a water-molecule will attract negative charge of atom of oxygen in adjacent water molecule. This attraction, called a hydrogen bond, will cause a type of bond between the molecules themselves.

Because of lack of charges, nonpolar compound won’t have the strength to break the hydrogen bonds between the water molecules. Therefore the nonpolar compound won’t combine with water.