Molecules and bonds can be classified in a variety of ways. Both can placed into the category of being polar or non-polar. For a molecule or bond to be polar, there has to be a separation of electric charge into two poles, one positive and one negative. A non-polar molecule or bond has a net electronegativity of zero and has a symmetrical charge.
Many polar molecules have a permanent dipole. A permanent dipole is when two atoms within a molecule have two different electronegativity amounts. One atom pulls the shared electrons closer to it, making it more negatively charged, and the other one more positive. This causes two ends of a molecule to become polar and have different charges. This makes the molecule unsymmetrical. The best example of this is a water molecule. The Oxygen molecule that shares electrons with the two hydrogen atoms is much more electronegative. It pulls the electrons closer to it than the hydrogen atoms do, and so the top end of the molecule becomes more negative and thus is polar. A molecule is non-polar, however, when the molecule is symmetrical and does not have an uneven distribution of charges. For example, carbon dioxide is a non-polar molecule. Carbon is in the middle, and the two oxygen atoms are on either side. The differences of electronegativity do not matter, however because, even though there are polar bonds within the molecule, they cancel out. The bonds are polar, but the molecule is symmetrical and thus not polar.
When a bond is polar, two different atoms that are covalently bonded have different electronegativity levels. The more electronegative atom pulls the shared electrons closer to it than to the other atom, making the bond polar. For example, in a bond shared between a chlorine atom and a hydrogen atom, the chlorine atom pulls the electrons closer to it. This makes the bond polar. An example of an non-polar bond would be between two hydrogen atoms bonding. Both have the same electronegativity, so there is a net electronegativity of zero.
The polarity of molecules and bonds is important for the chemical and geometric formations of larger molecules. Molecules that are polar can be platforms for strings of other molecules, such as the ones in proteins. The poles of these molecules help orient and attract other molecules. They also help scientists predict the orientation of larger molecules and their behaviors. Polar molecules are also important when predicting whether a mixture can become a solid. Either two polar molecules mixed together can create a solution, or two non-polar molecules mixed together. A mixture of polar and non-polar molecules will not. For example, water is a polar molecule and oil, a non polar molecule, meaning they will not create a solution.
Molecules and bonds that are polar, both are created by differences in electronegativity. Polar molecules are unsymmetrical and have an unbalance of changes. Non-polar molecules are symmetrical and have evenly distributed charges. Polar bonds do not have a net electronegativity of zero, whereas non-polar bonds do. Finally, the polarity of molecules is important because they serve as platforms for larger molecules and help predict the ability of a mixture to become a solution.