Bond Polarity and Inter-molecular interactions

Introduction

Polarity is the result of electrons being shared between the atoms. Sharing of electrons between the atoms can form either covalent or non-covalent bonds. Most of the covalent bonds involve in electron sharing irrespective of the nature of bonds between them.  The number of atoms joining together determine the bond character of the molecules, and this, in turn, determines the molecular properties of given atoms.

 

Polar covalent bonds

In polar covalent bonds, the bonding pairs of the electron are pulled between the nuclei of the atoms that help in sharing the atoms. Such a pull can create electronegativity which in turn adds some more imbalance between the atoms so that an opposing electron pull starts acting. So a polar molecule is formed usually when the one end of the molecule turned almost positive ant the opposite end of the molecule has negative charges. Such a difference in electric potential ends up creating an electrical pole.

 

Non-Polar covalent bonds

A nonpolar covalent bond is formed when the atoms experience an equal bond pull, and the bonding electrons are also shared equally.  Molecules of hydrogen, oxygen, and nitrogen have non-polar covalent bonds.  The table below helps to understand how bonds can be predicted based on the electronegativity. The degree of Polarity of bonds depends upon the relative electronegativity of participating atoms and the spatial arrangement of various bonds in the Atom. Because there is an electric difference between the 2 sides, it eventually leads to the movement of electrons towards the more electronegative element. 

 

Polarity of molecules and Intermolecular interactions

In the molecular polarity, a molecule can be polar as a result of the formation of polar bonds with differences in their electronegativity. Polarity can also result from the asymmetric arrangement of nonpolar covalent bonds and non-bonding pairs of electrons. Intermolecular force refers to the force that exists between the molecules of substances.  The van der Waals forces of attraction are a collection of forces such as the dipole-induced, dispersion forces and dipole-dipole forces. The ion-dipole and the ion-induced are not considered to be Van der Waal’s forces. There are 4 types of intermolecular interactions as a result of the polarity of, molecules. 

1. Dipole-Dipole interactions

 

Dipole-Dipole interaction forces mainly occur in polar molecules that have permanent dipoles. Here, the positive pole of the known molecule is normally attracted by the negative pole of the other molecule. For example, in HCl, chlorine is considered to be more electronegative while the hydrogen atom is positively charged. The figure below shows how dipole-dipole interactions take place in HCl molecules.

 

 

2. Ion-Dipole Interactions

Ion-Dipole interaction is the attraction between cations/anions and the polar molecules. Dissolving sodium chloride in water is a good example of ion-dipole interaction where the polar water molecules are attracted towards the sodium ions and the chloride ions.

 

                                          

3. Ion-induced dipole interactions

Here, an ion that is close to the non-polar molecule can get polarized, as a result, there is ion-induced dipole interaction.   For instance, the nitrogen ion can polarize the iodine molecule as illustrated below:

 

                                        

4. Dipole-induced dipole interactions

Dipole-induced dipole interactions involve a non-polar molecule being polarized by a polar molecule that is found within it. For instance, group O elements getting polarized in the presence of polar molecules as shown below.

 



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