Small molecules can be classied into nonpolar (e.g., CH4) and polar (e.g., H2O), based on the difference in the electronegativities between the bonded atoms. The nonpolar molecules contain atoms with similar electronegativities (like C and H), whereas in polar molecules, atoms with a wide difference of electronegativities (like C and O, H and O, or Al and Cl) are present. Polarity inuences the miscibility between compounds. Polar molecules are soluble in polar solvents while nonpolar molecules are miscible in nonpolar solvents (like hexane). On the other hand, polar molecules are insoluble in nonpolar solvents and vice versa.