Polarity – Polar and non-polar molecules

 

Polar Molecules

There are basically two types of covalent bonds, Non-polar and polar covalent bonds. Electronegativity can be used to explain the difference between these two types of covalent bonds.

Non-polar covalent bonds occur between two identical non-metal atoms, e.g. H2, Cl2, and O2. This is because the two atoms have the same electronegativity, the electron pair in the covalent bond is shared equally between them. However, if two different non-metal atoms bond then the shared electron pair will be pulled more strongly by the atom with the highest electronegativity. As a result.

Polar covalent bond

A polar covalent bond is formed where one atom will have a slightly negative charge and the other a slightly positive charge. This is represented using the symbols δ+ (slightly positive) and δ− (slightly negative). So, in a molecule such as hydrogen chloride (HCl), hydrogen is Hδ+ and chlorine is Clδ−.

Hcl molecules

Some molecules with polar covalent bonds are polar molecules, e.g. H2O. But not all molecules with polar covalent bonds are polar. An example is CO2. Although CO2 has two polar covalent bonds (between C+ atom and the two O− atoms), the molecule itself is not polar.

Polar molecule of H2O

Non polar molecule of CO2

The reason is that CO2 is a linear molecule and is therefore symmetrical. So there is no difference in charge between the two ends of the molecule. The polarity of molecules affects properties such as solubility, melting points and boiling points.

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