Methane, the main component of natural gas, is a nonpolar molecule. In it, four hydrogen atoms surround a single carbon in a three-dimensional arrangement shaped like a four-sided pyramid. The symmetry of the hydrogens on the corners of the pyramid evenly distribute electric charge on the molecule, making it nonpolar.

Molecules can be classified as polar or nonpolar. On a polar molecule, one side or area has more negative electric charge, making the opposite side positive. By contrast, a nonpolar molecule has a fairly uniform charge on its outside surface, making no side more negative or positive than another. Both the shape of the molecule and the type of bonds between atoms determine whether it’s polar or not.

On a polar molecule, the positive side attracts the negative side of a neighboring molecule, so that polar molecules clump together in small groups. For example, water, a polar molecule, forms snowflake crystals when it freezes. Polar molecules also absorb microwave radiation. That's why you can heat water in a microwave oven, whereas nonpolar molecules such as methane are typically transparent to microwaves.