Polar molecules such as water or ammonia attract one another in the same way that they attract other molecules of their own kind. The positive region of one molecule is attracted to the negative region of a neighbor, as shown on the right. Molecules of methane, CH₄, are nonpolar. If one of the -H groups in methane is replaced by an -OH, the molecule is methyl alcohol, CH₃-OH. This is a polar molecule, with a slight negative charge on the O and a slight positive charge on the H. Methyl alcohol and water molecules interact with one another, and hence mix well in solution. Each is a good solvent for the other.