Clathrate Compounds of Noble Gases: Properties, Applications and MCQs
Clathrate compounds of noble gases are solid compounds formed by physically trapping noble gas atoms (such as Argon, Krypton, Xenon) within the cavities or cages of crystal lattices of certain organic or inorganic host molecules or lattices. These compounds are also called host-guest or inclusion compounds because the host lattice provides the framework with cavities, and the noble gas atoms are the guest molecules trapped inside without forming chemical bonds.
Key Points on Clathrate Compounds of Noble Gases
Formation: Noble gas atoms are trapped in the cavities of crystal lattices of certain organic molecules (e.g., phenol, hydroquinone) or inorganic solids (e.g., zeolites, ice).
Nature: The guest noble gas atoms are physically enclosed; no chemical bonds form between host and guest.
Examples: Argon, Krypton, and Xenon form clathrates with organic compounds or zeolites. Helium generally does not form clathrates.
Types of Clathrate Compounds of Noble Gases
Organic clathrates with molecular hosts like phenol and hydroquinone.
Inorganic clathrates like noble gases trapped in zeolite or ice frameworks.
Types of Clathrate Compounds of Noble Gases
Organic clathrates with molecular hosts like phenol and hydroquinone.
Inorganic clathrates like noble gases trapped in zeolite or ice frameworks.
Properties of Clathrate Compounds of Noble Gases
- Clathrate compounds are formed by physically entrapping noble gas atoms inside the cavities of host lattice structures such as ice, quinol, phenol, hydroquinone, and zeolites.
- These noble gas atoms are not chemically bonded but mechanically trapped, resulting in so-called host-guest or inclusion compounds.
- The compounds are often non-stoichiometric, as not every cavity of the host lattice is completely filled.
- Clathrates are generally stable at low temperatures and moderate to high pressures.
- Their thermal stability increases down the noble gas group due to increased polarizability (e.g., xenon clathrates are more stable than argon).
- Heating or dissolution causes breakdown of the lattice and release of trapped gases.
- Their stability depends on dispersive van der Waals interactions between guest and host cage walls.
- Clathrate hydrates have cubic crystal structures with a guest:host molecular ratio typically around 1:6.
- Different crystal structures (Type I, II, and H) exist depending on the size of the guest and host cavities.
- Some clathrates can exhibit multiple guest occupancies inside a single cage, for example, hydrogen clathrates.
- Clathrate compounds are thermodynamically stable under specific pressure-temperature conditions where the free energy of formation is negative.
- They have applications in gas storage and separation, safe handling of radioactive isotopes, and advanced material design.
Applications of Clathrate Compounds of Noble Gases
- Separation and storage of noble gases.
- Radioactive isotope clathrates (e.g., Kr-85, Xe-133) are used as medical and industrial radiation sources.
- Important for understanding gas storage in natural gas hydrates and physiological processes.
Examples
| Type | Host Molecule/Structure | Noble Gas Guests | Notes |
|---|---|---|---|
| Gas Hydrates (Clathrate Hydrates) | Water (H2O) cages | Argon (Ar), Krypton (Kr), Xenon (Xe) | Hydrogen-bonded water cages physically trap noble gas atoms |
| Quinol Clathrates | Aqueous quinol solutions | Various noble gases | Formed under pressure and slow cooling of quinol solutions |
| Phenol and β-Hydroquinone Clathrates | Phenol, β-Hydroquinone crystals | Noble gases | Most stable organic clathrates; host forms cavities by hydrogen bonding |
| Zeolite Clathrates | Microporous aluminosilicate minerals (Zeolites) | Argon (Ar), Krypton (Kr), Xenon (Xe) | Inorganic clathrates with noble gases trapped in zeolite pores |
| Fullerene Endohedral Complexes | Carbon fullerene cages (e.g., C60) | Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe) | Noble gases trapped inside carbon cages, forming stable endohedral fullerenes |
Test Your Knowledge
1. Clathrate compounds of noble gases are:
a) Covalent compounds
b) Ionic compounds
c) Compounds formed by physical trapping of noble gas atoms in cavities
d) Metallic compounds
e) Gaseous mixtures
View Answer
c) Compounds formed by physical trapping of noble gas atoms in cavities
Explanation: These compounds do not involve chemical bonds but trap noble gases physically inside host lattice cavities.
2. Which of the following noble gases generally does NOT form clathrate compounds?
a) Argon (Ar)
b) Krypton (Kr)
c) Xenon (Xe)
d) Helium (He)
e) Radon (Rn)
View Answer
d) Helium (He)
Explanation: Helium's small size and very low polarizability make it incapable of forming stable clathrate compounds.
3. The host molecules in clathrate compounds typically:
a) Form strong chemical bonds with noble gases
b) Physically provide cavities to trap guest molecules
c) Are ionic crystals
d) Are noble gases
e) Easily evaporate at room temperature
View Answer
b) Physically provide cavities to trap guest molecules
Explanation: Hosts create cage-like structures that mechanically encage noble gas atoms without chemical bonding.
4. An example of an inorganic host forming clathrate compounds with noble gases is:
a) Phenol
b) Hydroquinone
c) Zeolite
d) Benzene
e) Graphite
View Answer
c) Zeolite
Explanation: Zeolites are microporous aluminosilicate minerals acting as inorganic host lattices trapping noble gases.
5. Clathrate hydrates involve:
a) Water molecules trapping noble gases
b) Carbon nanotubes trapping gases
c) Noble gases chemically bonding with water
d) Metals dissolved in water
e) Noble gases ionizing
View Answer
a) Water molecules trapping noble gases
Explanation: Hydrogen-bonded water cages enclose noble gases physically in clathrate hydrates without chemical reaction.
6. Endohedral fullerenes are clathrates where noble gases are trapped inside:
a) Water cages
b) Zeolite frameworks
c) Fullerene carbon cages (e.g., C60)
d) Hydroquinone crystals
e) Ice lattices
View Answer
c) Fullerene carbon cages (e.g., C60)
Explanation: Noble gas atoms can be trapped inside spherical carbon cages of fullerenes, forming stable endohedral compounds.
7. One application of noble gas clathrates is:
a) They serve as high-energy fuels
b) Storage of radioactive isotopes like Kr-85 and Xe-133
c) Catalysts in organic reactions
d) Making alloys
e) Increasing atmospheric pressure
View Answer
b) Storage of radioactive isotopes like Kr-85 and Xe-133
Explanation: Clathrates stabilize these radioactive noble gases, facilitating their medical and industrial use.
8. The stability of clathrate compounds:
a) Is due to strong covalent bonds
b) Is due to ionic bonding
c) Results from mechanical trapping of guest gases
d) Depends on chemical reaction between host and guest
e) Occurs only at very high temperature
View Answer
c) Results from mechanical trapping of guest gases
Explanation: Stability arises from physical enclosure within host lattices rather than chemical bonds.
9. Which of these noble gases is most likely to form clathrates?
a) Helium
b) Neon
c) Argon
d) All noble gases
e) None of these
View Answer
c) Argon
Explanation: Argon, being larger and more polarizable, forms clathrates more readily than the lighter He and Ne.
10. Clathrate compounds are often:
a) Stoichiometric compounds with fixed formula
b) Non-stoichiometric compounds where not all cavities are filled
c) Pure elements
d) Mixtures of liquids
e) Gaseous at room temperature
View Answer
b) Non-stoichiometric compounds where not all cavities are filled
Explanation: The occupation of cavities in host lattices is variable, leading to non-stoichiometric composition.