Why do homonuclear molecules \(\left(\mathrm{H}_{2}, \mathrm{Cl}_{2}, \mathrm{~N}_{2}\right.\), etc. \()\) have nonpolar bonds?

Imagine atoms in a tug-of-war for electrons. Electronegativity is essentially the 'muscle strength' that an atom has in this match. More formally, it's a measure of how strongly an atom can attract and hold onto the electrons shared within a chemical bond. Naturally, some elements are stronger 'players' than others.

When two atoms with different electronegativity values bond, the shared electrons are pulled more to one side. For instance, in a water molecule (H_{2}O), oxygen has higher electronegativity than hydrogen, so the shared electrons are closer to the oxygen atom, resulting in a polar bond.

Understanding electronegativity helps us to predict and explain the behavior of molecules during chemical reactions, such as why certain molecules are more reactive or why they have a particular shape.

Put two equally matched tug-of-war players on each end of the rope, and you'll have a standstill. This is the case with nonpolar bonds, where atoms have equal or almost equal electronegativity. They share the electrons equally since neither has a distinct advantage over the other.

H_{2} (hydrogen gas) is an example of a nonpolar molecule. The two hydrogen atoms have the same electronegativity and thus no 'tug' on the electrons is greater from one side than the other. The electrons are equally distributed, and as a result, the molecule doesn't have a positive or negative end.

Nonpolar bonds are significant in the formation of molecules that are symmetrical and in determining how substances will interact with different solvents, affecting solubility and melting points.

The Pauling scale is to electronegativity what the Richter scale is to earthquakes: it's a way of quantifying something's strength. It was developed by chemist Linus Pauling, and it assigns a number to each element that represents its electronegativity.

On this scale, fluorine reigns supreme with the highest value, which is arbitrarily set to 4.0. As a point of comparison, the value for hydrogen is 2.1. This scale helps chemists predict the types of bonds that will form in a molecule; the greater the difference between two atoms' electronegativity values, the more polar their bond is likely to be.

While it's not an absolute scale and other scales also exist, the Pauling scale is widely used due to its simplicity and practicality for predicting chemical bond polarity.

In the molecular world, a dipole moment is like a measure of the 'lopsidedness' of a molecule. It occurs in polar bonds, where there's an uneven distribution of electrons between the two atoms. This inequity creates a partial positive charge on one end and a partial negative charge on the other, much like a magnet with a north and south pole.

A molecule with a dipole moment typically aligns itself in an electric field with the positive end toward the negative plate and vice versa. The strength of the dipole moment is measured in debye units and indicates the degree of polarity. The larger the dipole moment, the more polar the bond. CO_{2} (carbon dioxide), despite having polar bonds, has a total dipole moment of zero because it is a linear molecule with two equal but opposite dipole moments that cancel each other out.