Polar Nonpolar?

Hi.

I am quite sure that there have already been answers to the polarity and classification of substances in polar or nonpolar substances.

First, for individual bonds within one molecule, it is determined whether these are polar or nonpolar. You know the so-called Pauling scale. There are electronegativity values for the elements. Carbon has, for example, the electronegativity 2.5, oxygen 3.5 and hydrogen 2.1. The electronegativity indicates how strongly it attracts the electrons in a covalent bond. The higher the electronegativity, the stronger this effect.

For example, if you have the substance methanol, you have the following bonds in the molecule: C-H, C-O and O-H. For each of these bonds, you can now calculate a so-called electronegativity difference (ΔEN):

• ΔEN(C-H) = 2.5 – 2.1 = 0.4
• ΔEN(C-O) = 3.5 – 2.5 = 1.0
• ΔEN(O-H)=3.5-2.1=1.4.

These values divide and now with how polar the individual bonds are. The following shall apply:

• ΔEN ≤ 0.4: nonpolar atomic bond
• 0.4 < ΔEN < 1.7: polar atomic bond
• 1,7 < ΔEN: ionic bond

This means that a nonpolar atomic bond is present at C-H, C-O and O-H are polar atomic bonds. In order to estimate whether the substance is more polar or nonpolar in total, we need to look at the proportion of polar and nonpolar bonds in the molecule. In methanol we have three nonpolar C-H bonds and two polar bonds. The polar fraction in the molecule therefore accounts for about half. So, methanol is a polar substance.

LG