Final answer:
Larger molecules exhibit stronger LDFs due to greater polarizability, leading to higher melting and boiling points. This is why hexane is a liquid while ethane is a gas. The overall state of a substance is influenced by the strength of its intermolecular forces.
Step-by-step explanation:
The statement, "The larger the molecule, the higher the intermolecular forces," refers to the concept that as the molecular size increases, the dispersion forces, or London Dispersion Forces (LDF), become stronger. This happens because larger molecules have a greater number of electrons which can become momentarily unevenly distributed, leading to temporary dipoles that contribute to attraction between molecules. Consequently, the strength of the intermolecular forces increases, which in turn tends to increase melting and boiling points. For example, while hexane is a liquid, ethane, with fewer electrons and a smaller size, is a gas. This is due to hexane having stronger dispersion forces because of its larger size and mass.
Larger molecules also have greater polarizability, which means their electron clouds are more easily distorted, enhancing the temporary dipole interactions. Consequently, substances with large molecules, such as decane or eicosane, tend to be liquids or solids at room temperature due to their strong LDFs in contrast to smaller molecules like methane or ethane that are gases at room temperature.
Role of Molecular Size
The intermolecular forces such as LDFs dictate whether a substance will be in the solid, liquid, or gas state under normal conditions. The melting and boiling points of substances are also influenced by the strength of these forces, which is why the boiling point of CS₂ is higher than that of CO₂ and substances like water exhibit high surface tension due to their strong hydrogen bonds.