There are different types of intermolecular forces that play a crucial role in determining the properties of organic compounds. One of the important intermolecular forces is the instantaneous dipole-induced dipole forces, also known as id-id forces. These forces arise due to the temporary instantaneous dipoles induced in both polar and non-polar molecules.
Instantaneous Dipole-Induced Dipole Forces
Instantaneous dipole-induced dipole forces are the weakest intermolecular attractive force and result from temporary dipoles induced in molecules. These forces are also referred to as London dispersion forces or temporary dipole-temporary dipole forces. The dipoles formed as a result of these forces are not permanent and are constantly changing as the electron clouds within the molecules are in constant motion.
Causes and Examples of Instantaneous Dipole-Induced Dipole Forces
The id-id forces increase with an increasing number of electrons and protons in the molecule. As the electron movements in atoms result in temporary dipole-dipole forces, the attraction between molecules increases with an increasing number of electrons. Similarly, the id-id forces increase with the enthalpy of vaporization and the increasing number of contact points between the molecules. The contact points are places where the molecules come close together, resulting in a higher boiling point.
One example of the impact of id-id forces on boiling points is evident when comparing the boiling points of pentane and 2,2-dimethylpropane. Pentane, with a boiling point of 36°C, has fewer contact points compared to 2,2-dimethylpropane, which has a boiling point of 10°C due to more contact points. Additionally, the total id-id forces between long non-polar molecules such as poly(ethene) can be much larger, resulting in a solid-state at room temperature.
Permanent Dipole-Permanent Dipole Interaction
In addition to instantaneous dipole-induced dipole forces, dipole-dipole forces are another type of intermolecular force that arises due to the interaction between permanent dipoles in different molecules. These forces are stronger than the id-id forces and depend on the polar nature of the molecules.
Ion-Dipole Forces
Ion-dipole forces are present in mixtures of ionic compounds and polar compounds. These forces play a significant role in various chemical reactions and interactions between ionic and polar substances.
Trend in Boiling Points of Organic Compounds
The trend in boiling points of organic compounds depends on various factors, including the intermolecular forces present in the molecules. The boiling point of organic compounds increases with an increasing number of electrons, resulting in stronger id-id forces. Additionally, branching decreases the boiling point of organic compounds due to the reduced contact points between the molecules.
In summary, understanding the types of intermolecular forces, such as instantaneous dipole-induced dipole forces, dipole-dipole forces, and ion-dipole forces, is essential for comprehending the behavior and properties of organic compounds. These forces have a significant impact on various physical and chemical properties, including boiling points and intermolecular interactions.
