Group 18 consists of the elements, helium, neon, argon, krypton, xenon, and radon, which are collectively known as noble gases. Due to their chemical inactivity they are also called inert gases.
Occurrence and isolation
Atmospheric air is the major source of noble gases. Radon is not found in atmosphere and is obtained as thee decay product of 226Ra. The total abundance of noble gases in dry air is approximately 1%.
Neon, Argon, Krypton and Xenon are obtained by the liquefaction of dry air and separation of its constituents by fractional distillation. Helium is isolated from natural gas. When natural gas is compressed and liquefied, Helium remains along with unliquefied gas, which contains 2% nitrogen as impurity. N2 is removed by adsorption on charcoal at – 1900C.
Atomic and physical properties
Electronic configuration
Except Helium, all other noble gases have ns2np6 configuration. The electronic configuration of He is IS2. Due to this stable electronic configuration, they have less tendency to take part of in chemical reactions.
Atomic radius
The atomic radii of noble gases are taken as van der Walls radius. As we move down the group atomic radii increases due to the increase in number of shells.
Ionization energy
Group 18 elements have highest ionization energy in their respective periods due to their stable noble gas configuration. Thus is one of the reasons for their less reactivity. Ionization energy decreases on moving down the group due to increase in atomic size.
Electron affinity
Due to stable closed shell configuration ns2 np6, noble gases have no tendency to accept additional electron. Therefore electron affinity of noble gases is almost equal to zero. This also makes them reluctant towards chemical reaction.
Liquefaction
The tendency for liquefaction of noble gases increases on moving down the group due to increase in vander Waal's force with increase in size of atom.
Uses Of Noble Gases
The important uses of Noble gases are
1. Helium is used for filling balloons and airships.
2. Helium is used for producing inert atmosphere in certain processes such as metallurgical operations.
3. Liquid Helium is used as cryogenic agent for carrying out various experiments at low temperatures.
4. Argon is used to provide inert atmosphere in high temperature metallurgical operation and used for filling electric bulbs.
5. Neon is used in discharge tubes and fluorescent bulb for advertisement display purpose.
6. Radon is used in radio therapy for the treatment of cancer.
7. Xenon and Krypton has no significant uses except that are used in certain light bulbs for special purpose.
Related article P - block elements
No comments:
Post a Comment