The boiling point of a substance is the temperature at which it changes from a liquid to a gas. Several factors can affect the boiling point, including the strength of intermolecular forces, molecular size, and molecular shape. By understanding these factors, we can predict the boiling point of a substance based on its intermolecular forces.1. Intermolecular forces: Intermolecular forces are the forces that hold molecules together in a substance. The stronger the intermolecular forces, the higher the boiling point. There are three main types of intermolecular forces: dispersion forces also known as London forces , dipole-dipole forces, and hydrogen bonding. a. Dispersion forces: These are the weakest intermolecular forces and occur between all molecules, including nonpolar molecules. Dispersion forces result from temporary fluctuations in electron distribution, which create temporary dipoles. The strength of dispersion forces increases with the size of the molecule. b. Dipole-dipole forces: These forces occur between polar molecules, which have a permanent dipole due to differences in electronegativity between atoms. Dipole-dipole forces are stronger than dispersion forces and result in higher boiling points for polar substances compared to nonpolar substances of similar molecular size. c. Hydrogen bonding: This is a special type of dipole-dipole interaction that occurs between molecules containing a hydrogen atom bonded to a highly electronegative atom such as oxygen, nitrogen, or fluorine . Hydrogen bonding is the strongest of the three intermolecular forces and results in significantly higher boiling points for substances that exhibit hydrogen bonding.2. Molecular size: Larger molecules have more electrons and a larger surface area, which leads to stronger dispersion forces. As a result, larger molecules generally have higher boiling points than smaller molecules with similar intermolecular forces.3. Molecular shape: The shape of a molecule can affect its boiling point by influencing the strength of its intermolecular forces. Molecules with a more extended shape have a larger surface area, which can lead to stronger dispersion forces and higher boiling points. In contrast, compact or spherical molecules have a smaller surface area, resulting in weaker dispersion forces and lower boiling points.Examples:1. Comparing boiling points based on intermolecular forces: - Methane CH4 is a nonpolar molecule with only dispersion forces. Its boiling point is -161.5C. - Ammonia NH3 is a polar molecule with dipole-dipole forces and hydrogen bonding. Its boiling point is -33.34C. - Water H2O is a polar molecule with strong hydrogen bonding. Its boiling point is 100C.2. Comparing boiling points based on molecular size: - Propane C3H8 is a larger nonpolar molecule than methane CH4 . Propane has a boiling point of -42C, which is higher than methane's boiling point of -161.5C.3. Comparing boiling points based on molecular shape: - n-Butane C4H10 is a linear molecule with a boiling point of -0.5C. - Isobutane C4H10 is a branched isomer of n-butane with a more compact shape. Its boiling point is -11.7C, which is lower than n-butane's boiling point due to its weaker dispersion forces.