Molar mass usually indicates the size of the molecule. The heavier the molecules, the greater the London forces and the more likely weare to find it in the liquid or solid state at a given temperature. For example, at room temperature, Natural gas, CH4, Has a molar mass of 16g/mol. Ocatane, C8H8, a major component of gasoline, is a liquid and has a molarmass of 114g/mol. Paraffin, C24H50, is a solid and has a molar mass of 288 g/mol. The higher molecular weight (paraffin) with consequent larger molecules will hvae greater intermolecular forces of attraction, hence higher melting and boiling points than substances with lower molecular weight. For example, the boiling point of Whereas dipole-dipole attractions usually do not have hydrogen bonding has. Consider the water molecules. It Has a ver small molar mass of 18 g/mol. Of only London forces are present, it would be a gas at a temperature as law as - 75 C. Even if regular dipole-dipole attractions are present, it would still boil at a ver low temperature. The force of attraction that holds the water molecules together so that it exists as a liquid at room temperature and even a solid at 0 C is hydrogen bonding. Another importance of hydrogen bonding is in the complex  huge molecules, Which are the basis of life. Plants, animals, and man have nucleic acid with DNA . Let us consider for example a molecule of DNA, the messenger of life. It is a very large molecule composed of two strands of covalently bonded atoms arranged in a helix, somewhat like a spiral staircase. These two strands can separate molecules. They can separate because they are held together by hydrogen bonds just like "Velcro" holds two pieces of clothing together. The hydrogen bonds are not as strong as the covalent bonds within the strands. Intermolecular forces of attraction also have a strong influence on the solubility of a subtance. Polar solvents dissolve ionic or polar molecular compounds, whereas nonpolar solvents dissolve nonpolar compounds. for example if we want to remave a grease stain (grease is composed of nonpolar molecules), we know that water foes not work but a nonpolar solvent , such as gasoline, does.