Question

Although the noble gas elements are monatomic and could not give rise to dipole-dipole forces or hydrogen bonding, these elements still can be liquefied and solidified. Explain.

Short answer

Noble gas elements can be liquefied and solidified due to the presence of London dispersion forces, which are weak, temporary attractive forces between atoms caused by the random motion of electrons. As the temperature decreases, these forces become dominant, allowing noble gas atoms to form liquids and solids despite being monatomic and nonpolar.

Step-by-step solution

Intermolecular forces

There are three types of intermolecular forces: London dispersion forces, dipole-dipole forces, and hydrogen bonding. The noble gases are monatomic, meaning they consist of a single atom, and are nonpolar, meaning they do not have a positive and negative charge distribution. As such, they do not have dipole-dipole forces or hydrogen bonding. However, they do experience London dispersion forces.

London dispersion forces

London dispersion forces are temporary attractive forces between atoms and molecules caused by the random motion of electrons. These forces are present in all atoms and molecules, including noble gases. Because noble gas atoms have a spherical electron cloud, they can experience dispersion forces, and their magnitude increases as the electron cloud becomes more polarizable (affecting the size of the noble gases).

Liquefying and solidifying noble gases

In order for a substance to change from one phase (gas, liquid, solid) to another, the intermolecular forces present in the substance must be overcome or become dominant. As we lower the temperature of a noble gas, the kinetic energy of its atoms decreases, and the London dispersion forces start to dominate. These forces are weak but are still strong enough to hold noble gas atoms together when the temperature is low enough, allowing them to form liquids and solids.

Conclusion

Noble gas elements can be liquefied and solidified because they experience London dispersion forces, which are temporary attractive forces between atoms. These forces increase in strength as the temperature decreases, eventually becoming strong enough to hold the noble gas atoms together in liquid or solid-phase.