[Physics Class Notes] on Dielectric Material and Dipole Moment Pdf for Exam

Dipole moment occurs when atoms in the molecule share electrons unequally. It happens when one atom in the molecule has a higher electronegativity than the other. The electronegative atom pulls the shared pair of electrons more tightly, or the atom with lone pair of electrons can point the electronegativity vector in the same way. Higher the difference in electronegativity means more significant dipole moment. Let’s take the example of a water molecule that contains two hydrogen atoms and one oxygen atom to understand this topic more clearly.  Oxygen has a lone pair of electrons and has a higher electronegativity than oxygen. It gives hydrogen a partial positive charge and oxygen a partial negative charge. 

Insulators and Dielectric Material

Dielectric materials are substances that are very poor conductors of heat or electricity. No current will flow in the dielectric if we place them in the electric field. It is because they do not contain any free or loosely bound electrons like metals. However, electric polarization can still occur in some insulators. In simple words, the insulators that undergo electric polarization when we apply an electric field are known as dielectrics. Hence, it is essential to note that every insulator material is not a dielectric substance. In dielectrics, the charges do not move but show a slight displacement from their equilibrium position. The presence of polar molecules in dielectrics leads to polarization.

Other Electric phenomena also change due to the presence of a dielectric substance. If we compare the force between two electric charges in a vacuum and dielectric medium, it will be less in a dielectric medium. Moreover, the dielectric medium has a higher amount of energy stored in an electric field per unit volume. If you fill any capacitor with a dielectric material, then it would have higher capacitance than a vacuum.   

Polarity

The polarity of a molecule refers to the property by which the distribution of charge takes place between its atoms. The separation of electric charge in a molecule results in the formation of an electric dipole. The polarity of the bond arises due to the difference in electronegativity between the atoms taking part in bond formation. In simple words, electronegativity refers to the power of an atom by which it attracts the electrons towards itself during bond formation. If the difference in electronegativity between two atoms is less than 0.4, then they show no dipole moment. The molecule has a dipole moment and polarity. if the difference in electronegativities of its particles is more than 0.4.

Difference Between Polar and Nonpolar Molecules in Physics

The molecules in which there is an equal distribution of electric charges between the atoms are non-polar. The particles present in these molecules have similar levels of attraction due to which their electrical charges coincide in the centre. The lack of polarity in non-polar molecules can be because of two reasons. The first reason can be the presence of a non-polar bond. The other one can be the symmetry of the particles, which can lead to the cancellation of the polar charge. In H2 or O2, the non-polar bond is present, which makes them non-polar molecules. The CO2 comprises the polar bond, but it is still non-polar because of the cancellation of charges due to its symmetrical structure. If the difference in electronegativity of two atoms is too high, then it leads to the formation of the ionic bond. In this type of bond formation, the complete transfer of electrons takes place rather than the sharing of electrons.

The above image shows the structure of a carbon dioxide molecule. The red part represents the oxygen atom, whereas the black part represents the carbon atom. It is a non-polar molecule because of its linear and symmetric structure. 

The polar molecules are the ones that have the centres of positive and negative charges. These opposing charges can result in a net dipole moment and polarity. The asymmetric bonds can also lead to the polarity in the molecules. Some of the popular examples of polar molecules include Ammonia (NH3), Ozone (O3), Water (H2O) etc. The cancellation of the dipole is not possible in polar molecules due to the exertion of force due to charges on atoms. A polar solvent can dissolve other polar molecules easily. The random orientation of dipole moment throughout the molecule leads to the cancellation of net polarity. However, the dipole in the polar molecule aligns itself in the direction of the electric field during its presence. 

The above image shows the polar nature of the water molecule made of oxygen and hydrogen. The electronegativity of oxygen is 3.44, and hydrogen is 2.20. It makes the molecule of water polar. Here, the blue represents the partially positive charged region while the red represents the negatively charged ones.