Question

Why does solid iodine sublime readily? Use your knowledge of intermolecular forces to explain.

Short answer

Solid iodine sublimes readily due to the presence of weak London dispersion forces as the primary intermolecular force between I2 molecules. Although stronger than in smaller molecules, they are still weaker than hydrogen bonding or dipole-dipole interactions, requiring minimal energy for the phase change from solid to gas. This allows iodine molecules to easily break away from the crystal lattice structure and enter the gas phase when energy is added as heat.

Step-by-step solution

Identify Intermolecular Forces in Iodine

Before we can explain why solid iodine readily sublimes, we need to identify the types of intermolecular forces present within iodine. Iodine exists as a diatomic molecule, I2, formed by the covalent bond between two iodine atoms.

Discuss London Dispersion Forces in Iodine

The primary intermolecular force present in iodine is London dispersion forces (also known as van der Waals forces). London dispersion forces are temporary attractive forces that result from the constant motion of electrons and the creation of temporary dipoles. These forces are generally weak and depend on the surface area and the proximity between the molecules. Since iodine is a relatively large molecule with a significant electron cloud, the London dispersion forces are stronger in comparison to smaller molecules.

Describe the Structure of Solid Iodine

As a solid, iodine forms a crystal lattice structure. This arrangement allows the molecules to stack together, with each iodine molecule interacting with its neighbors through London dispersion forces.

Compare Intermolecular Forces in Iodine to Other Substances

Though London dispersion forces in iodine are relatively stronger than in smaller molecules, they are still weaker than other types of intermolecular forces such as hydrogen bonding or dipole-dipole interactions. This means that, in general, substances with these stronger intermolecular forces have higher boiling points and melting points compared to iodine.

Relate Intermolecular Forces to Iodine's Sublimation

The strength of the intermolecular forces in a substance determines the amount of energy needed to change its state from solid to liquid or from liquid to gas. Due to the weak nature of the London dispersion forces, the energy needed to cause the phase change from solid to gas in iodine is minimal. As a result, iodine sublimates easily when energy is added as heat. In summary, the weak London dispersion forces present in iodine make it easier for the iodine molecules to break away from their crystal lattice structure and enter the gas phase, causing iodine to readily sublime.

Key concepts

London Dispersion Forces

London dispersion forces, sometimes known as van der Waals forces, are among the weakest types of intermolecular forces that occur between molecules. These forces are temporary and arise due to the random, momentary distribution of electrons within a molecule, which creates temporary dipoles. These dipoles induce further dipoles in neighboring molecules, leading to a fleeting attraction. Although they are generally the weakest form of intermolecular attraction, London dispersion forces become significantly stronger as the size and mass of the molecules increase due to larger electron clouds.

In the case of iodine (\( I_2 \)), which is a relatively large molecule with a significant number of electrons, the electron cloud is large enough to generate relatively stronger London dispersion forces compared to smaller molecules. However, because they are still not as strong as hydrogen bonds or dipole-dipole interactions, substances like iodine that primarily rely on London dispersion forces tend to have lower melting and boiling points.

Sublimation

Sublimation is the process of a substance transitioning directly from a solid state to a gaseous state without passing through the liquid state. This is an uncommon phase change, often occurring under conditions where the intermolecular forces within a solid are not strong enough to maintain a liquid state before the molecules escape into a gas.

For iodine, which exists in a solid state with a crystalline structure, sublimation occurs with relative ease. The London dispersion forces holding the iodine molecules together are weak, meaning it requires only a small amount of energy to supply the heat needed for the iodine molecules to break free from their lattice arrangement.

• This makes iodine an ideal example of a substance that sublimes readily under standard atmospheric conditions.
• This characteristic is exploited in various applications such as in chemical reactions where sublimation is used for the purification of iodine.

Understanding sublimation can help predict the behavior of other similar molecular substances under varying thermal conditions.

Iodine

Iodine is a halogen located in group 17 of the periodic table, known for its distinct deep purple crystalline structure when solid. Despite its solid state at room temperature, iodine sublimates, which means it has a tendency to transform directly to a gas under certain conditions by bypassing the liquid phase.

Its diatomic nature (\( I_2 \)) features two iodine atoms bonded covalently, and in the solid state, these molecules align in a crystal lattice held together primarily by London dispersion forces. These characteristics of iodine lead to its unique sublimation properties, as the weak forces require less energy to move iodine from a solid to a gaseous state.

• Iodine's ease of sublimation can cause it to release a characteristic violet vapor, which can be observed readily when the solid is gently heated.
• This behavior is utilized in practical applications such as in antiseptics and nutritional supplements.

Understanding these properties of iodine can enhance knowledge of its practical uses and reactions in both industrial and laboratory settings.