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The important trends observed in the chemical behavior of group 13 elements are 1. Group 13 elements form hydrides of the type MH 3 . Thermal stability of hydrides decreases as we move down the group. Hydrides act as weak lewis acids. Boron forms a number of hydrides known as boranes. The important series among boranes are nido-boranes (B n H n+4 ) and arachno-boranes (B n H n+6 ). Aluminium and Galium can form tetra hydrido anions (MH 4 -).[LiAlH 4 ] is an example for this and is a good reducing agent used in organic synthesis. 2. The elements of group 13 form trihalides of the type MX 3 . The trihalides are strong Lewis acids. The flurides are ionic and have high melting points. The chlorides, bromides and iodides are covalent compounds with low melting points. Halides can exist in dimeric form with halogen bridges. 3. All the elements of group 13 form oxides with formula M 2 O 3 and hydroxides of the type M(OH) 3 . Basic character of oxides and hydroxides increases as we move down...

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...