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Give important trends and anomalous properties of boron. |
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Answer» Solution :Certain important trends can be observed in the chemical behaviour of group-13 elements. The trichlorides, bromides and iodides of all these elements being covalent in NATURE are hydrolysed in WATER. Species like tetrahedral `[M(OH)_4]^(-)`and octahedral `[M(H_2O)_6]^(3+)` , except in boron, exist in aqueous medium. The monomeric trihalides, being electron DEFICIENT, are strong Lewis acids. Boron trifluoride easily reacts with Lewis bases such as `NH_3` to COMPLETE octet around boron. It is due to the absence of d-orbitals that the maximum covalence of B is 4. Since the d orbitals are available with Al and other elements, the maximum covalence can be expected beyond 4. Most of the other metal halides (e.g., `AlCl_3`) are dimerised through halogen BRIDGING (e.g., `Al_2Cl_6`). The metal species completes its octet by accepting electrons from halogen in these halogen bridged molecules. |
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