what is bents rule?? how does it affect the s character and p character of the atomic orbitals,how is bents rule used to determine shapes and bond angles,in an compound...and why does more elctronegative atom takes more p character leaving behind s character on central atom??

saswat nayak, 11 years ago

Grade:12

1 Answers

ruchi yadav

askIITians Faculty 27 Points

10 years ago

Bent's ruledescribes and explains the relationship between theorbital hybridisationsof central atoms in molecules and theelectronegativitiesofsubstituents.The rule was stated by Henry Bent as follows: "Atomic s character concentrates in orbitals directed toward electropositive substituents".

Thechemical structureof amoleculeis intimately related to its properties and reactivity.Valence bond theoryproposes that molecular structures are due tocovalent bondsbetween theatomsand that each bond consists of two overlapping and typicallyhybridised atomic orbitals. Traditionally,p-blockelements in molecules are assumed tohybridisestrictly as spⁿ, wherenis either 1, 2, or 3. In addition, the hybrid orbitals are all assumed to be equivalent (i.e. the $n +1$ spⁿorbitals have the same p character). Results from this approach are usually good, but they can be improved upon by allowing hybridised orbitals with noninteger and unequal p character. Bent's rule provides a qualitative estimate as to how these hybridised orbitals should be constructed.Bent's rule is that in a molecule, a central atom bonded to multiple groups will hybridise so that orbitals with more s character are directed towards electropositive groups, while orbitals with more p character will be directed towards groups that are more electronegative. By removing the assumption that all hybrid orbitals are equivalent spⁿorbitals, better predictions and explanations of properties such asmolecular geometryand bond strength can be obtained.

Bent's rule can be generalized tod-blockelements as well. The hybridisation of a metal center is arranged so that orbitals with more s character are directed towardsligandsthat form bonds with more covalent character. Equivalently, orbitals with more d character are directed towards groups that form bonds of greater ionic character.