Question

Discuss the formation of clathrates by noble gases.

Short answer

Clathrates are cage-like structures formed when a 'guest' molecule, such as a noble gas, is trapped inside a 'host' molecule's structure, often a water molecule. Noble gases can form clathrates due to their non-reactivity and stable electron configurations. The process usually occurs under high pressure and low temperature conditions, with the weak Van der Waals forces holding the structure together.

Step-by-step solution

Clathrate Formation

Clathrates are cage-like structures formed by certain substances where a 'guest' molecule is trapped inside a 'host' molecule's structure. Noble gases can be the 'guest' molecules in these structures. When a host substance, often a water molecule, surrounds and traps the guest gas molecule, a clathrate is formed.

Role of Noble Gases

Noble gases such as helium, neon, argon, krypton, and xenon can form clathrates. These gases are non-reactive and have stable electron configurations, which allow them to be captured effectively within the host substance without reacting and breaking the cage structure. The weak Van der Waals forces between the noble gas atoms and host molecules hold the clathrate structure together.

Specific Formation of Clathrates by Noble Gases

The formation process usually occurs under high pressure and low temperature conditions. The noble gas atoms get trapped in the cavity of the host as the host crystallizes into its lattice structure. This process results in a solid clathrate hydrate, consisting of a network of polyhedral water molecules encapsulating noble gas atoms. Most notably, these clathrates can occur naturally in permafrost or deep-sea sediments.

Key concepts

Noble Gases

Noble gases, which include elements such as helium, neon, argon, krypton, and xenon, are known for their lack of chemical reactivity. This characteristic is due to their full valence electron shells, which provide a stable electronic configuration. As such, these gases do not readily form chemical bonds with other elements.

Noble gases are perfectly suited to be 'guest' molecules in clathrate formations because their stability ensures they can be encased within 'host' structures without altering the chemical integrity of either the host or the guest. In the natural world, when conditions are right - particularly under low temperatures and high pressure - these gases can become trapped within clathrate structures, leading to the formation of noble gas clathrates. Examples include frozen structures beneath permafrost or within ocean sediments, which are significant because they can trap substantial quantities of noble gases.

Cage-like Structures

Clathrates consist of 'cage-like' structures formed by a network of 'host' molecules that encompass 'guest' molecules within. These hosts are typically water molecules that, under certain conditions, bond to each other to form a polyhedral lattice.

Imagine the this cage as a spherical soccer ball, where the panels represent the host water molecules, and the inside of the ball is a space where a noble gas atom can reside. The cage-like structure is maintained not by strong covalent bonds, but by intermolecular forces, which are sufficient enough to stabilize the guest molecule within the host lattice. Such structures are significant in the natural storage and containment of gases and can be found in various environmental conditions, from the icy tundra to the depths of the sea.

Van der Waals Forces

Van der Waals forces play a pivotal role in the formation and stability of clathrate structures. These are the weak forces of attraction that exist between molecules or atoms, which include London dispersion forces, dipole-dipole interactions, and hydrogen bonds.

Although weaker than covalent or ionic bonds, Van der Waals forces are the glue that holds the clathrate's host and guest molecules together. Without these forces, the neatly organized cage structure would not be capable of trapping noble gases. In the case of noble gas clathrates, the lack of strong covalent bonds is actually an advantage as it allows for the encapsulation of the gases without the necessity of forming a new compound. These delicate yet essential forces are what enable the formation of clathrates under certain environmental pressures and temperatures, maintaining their integrity until those conditions change.