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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 t...

Elements of group 13 to 18 of the long form of the periodic table from the P-block elements. In the 'P' block elements, the last electron enters into the 'p' orbital of the outermost shell. 'p' block elements are coming under representative elements along with 's' block elements. They are called so, because they exhibit regular trends in properties with in each group and period. Some general characteristics of 'p' block elements Atomic and ionic radii of 'p' block elements decrease on moving from left to right and increase from top to bottom in any group. Along a period, there is a progressive increase in the nuclear charge of the atoms while the electrons are added to same outer most shell. This causes a decrease in atomic size from left to right along a period. Down a group the effective nuclear charge decreases due to addition of new shells and this results is an increase of atomic size.Ionization enthalpy of 'p' block elements...