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In chemistry, polarity refers to the distribution of electric charge across a molecule. A molecule is polar if it has a positive end and a negative end, typically due to differences in electronegativity between its atoms. Water is a classic example of a polar molecule. Its oxygen atom is highly electronegative compared to hydrogen, which creates a partial negative charge on the oxygen and a partial positive charge on the hydrogens.
This charge separation allows polar molecules to attract other polar molecules or ions through dipole-dipole interactions. As a result, polar substances are often soluble in polar solvents, like water. This characteristic is summed up in the principle "like dissolves like," where substances with similar properties, such as polarity, are more likely to dissolve in one another.

Hydrocarbons are organic compounds composed solely of hydrogen and carbon atoms. These compounds, such as the ones found in gasoline, belong to the class of nonpolar substances. The carbon and hydrogen atoms in hydrocarbons have similar electronegativities, which means there is little difference in charge across the molecule.
Due to their nonpolar nature, hydrocarbons do not engage in strong interactions with water molecules. Instead, they prefer to cluster together, avoiding the polar molecules in the surrounding environment. This behavior is why hydrocarbons like gasoline are "hydrophobic" or "water-fearing," and they do not mix well with water.

Water is often referred to as the "universal solvent" due to its ability to dissolve a wide range of substances. This is mainly because of its polarity. The molecular structure of water includes a bent shape that results in significant dipole moments, where an uneven distribution of electron density across the water molecule leads to positive and negative regions.
These polar characteristics enable water molecules to surround and interact with ions and other polar molecules, pulling them into solution. However, this powerful solvency does not extend to nonpolar substances like hydrocarbons. The lack of polar sites in hydrocarbons means there is no favorable interaction with water, explaining why substances like gasoline remain insoluble in it.