Chemistry of Nobel Gases

Chemistry of Nobel Gases

Noble gases are present in group 18 of the modern periodic table. They all are colourless, odourless and tasteless. Under normal conditions, they are in a gaseous state. They are monatomic gases (C_p/C_v = 1.67) because they don't form molecules very easily due to their stable electronic configuration. Their outer most configuration is ns² and ns²np⁶. The first three elements Helium, Neon and Argon called inert gases while the last three elements Krypton, Xenon and Radon are are called nobel gases. Xe is the most reactive noble gas and exhibits all even oxidation states from +2 to +8.

Element	Symbol	Atomic No.	Valence shell electronic configuration
Helium	He	2	1s2
Neon	Ne	10	[He] 2s22p6
Argon	Ar	18	[Ne] 3s23p6
Krypton	Kr	36	[Ar] 3d104s24p6
Xenon	Xe	54	[Kr] 4d105s25p6
Radon	Rn	86	[Xe] 4f143d106s26p6

Physical properties of noble gases

Here are some physical properties of noble gases:

Atomic Size or Atomic Radii
Atomic radii increases on moving down the group from He to Rn because as we move down the group, occupied shells increase in number.

Melting and boiling point
Under normal conditions of temperature and pressure, all the noble gas elements are in the gaseous state. All of the noble gases have very low melting and boiling points. However, as we move down the group, the melting and boiling point increases because of the increase in atomic size.

Density
All the noble gas elements have low densities. However, as we move down the group, the density will increase again due to an increase in atomic size.

Ionisation potential
As we move down the group from He to Rn, atomic size increases which result in an increase in the attractive force and thus, the polarity increases and ionisation potential decreases.

Heat and electricity conductivity
All the noble gases conduct electricity except neon. All of them are, however, poor heat conductors.

Reactivity of Zero Group Elements

He and Ne are chemically inert and they do not form any compounds due to very high ionization energy, zero electron affinity and the absence of vacant d-orbitals in valence shell.

Ar, Kr and Xe will show some reactivity due to low ionization potentials and presence of vacant d-orbitals in valence shell.
Xe is more reactive than Ar and Kr due to it's low ionisation energy.

Krypton forms only one known stable neutral molecule KrF₂. Xe shows tendency to lose electrons in many of it's reactions. Therefore, Xe combines with only more electronegative elements like F and O or electronegative groups. Xe does not combine with less electronegative elements like Cl₂ or N₂.

Radon is radioactive and it will not show chemical reactivity.

Clathrates of Nobel Gases

A number of organic and inorganic compounds having noble gases trapped into the cavities of crystal lattices are called clathrate compounds. They are also known as cage compounds,

The substance having cavities in crystal lattices is called the host and atom of noble gases entrapped in it is called the guest which are held by Van der waals forces of attraction. The clathrates are non stoichiometric compounds. When clathrates are heated or dissolved the guest atom escapes from the host.
He and Ne do not form clathrates due to their small size.

Clathrates are of two types.
Gas hydrates - Solid water having entrapped Ar, Kr, or Xe
Quinol Clathrates - Quinol having entrapped Ar, Kr, and Xe

Uses of Clathrates of Nobel Gases

Clathrates of noble gases are used for the storage and transportation of noble gases due to their ability to trap these gases within a crystalline structure, making them easier to handle and transport compared to their gaseous state.

Separation of noble gases - Since Ne does not form a clathrate with Quinol it is separated from Ar, Kr and Xe. The latter form a clathrate with quinol.

Xe - 133 clathrate is a source of γ- radiations
Kr - 85 clathrate is a source of β - radiations
As an anaesthetic - Xe clathrate is used for this
For transporting isotopes of noble gases.

Structures of Xenon Compounds

The structure of xenon compounds can be explained on the basis of the VSEPR theory as well as the concept of hybridization. The structures of oxyfluorides and oxides of xenon can best be explained by the concept of hybridization. The types of hybridization in these molecules and their shapes are also listed in the below table.

Compounds	Formula	Hybridization	Structure
Xenon difluoride	XeF2	sp3d	Linear
Xenon tetrafluoride	XeF4	sp3d2	Square Planar
Xenon hexafluoride	XeF6	sp3d3	Distorted octahedral
Xenon oxydifluoride	XeOF2	sp3d	T-shape
Xenon oxytetrafluoride	XeOF4	sp3d2	Square pyramidal
Xenon trioxide	XeO3	sp3	Tetrahedral

Also read Preparation, Properties and Geometry of Fluorides of Xenon
Hydrolysis of Xenon Fluorides and Factors Affects Hydrolysis
Applications of Noble Gases
Chemistry of Noble Gases MCQs