1. Topic : Bent’s Rule
By : Aman Kumar
M.Sc. Integrated Chemistry
2. Bent’s Rule
Bent’s rule describes and explains the relationship between the orbital
hybridization of central atoms in molecules and the electronegativities
of substituents. The rule was started by Henry Bent as follow : more
electronegativity element prefer hybrid orbital having less s character
and more p character while less electronegative substituents prefer
hybrid orbital having more s character.
Examples ; CH4 , CH3F
3. Example fluoromethane justification
Due to non – uniform distribution of % S character the bond angle
change due to decreases % S character in F- bond the bond angle
decreases.
4. Application of bent rule
• Bond length : Bond length depends upon the
hybridization of the atom. Let’s take an example
of chloromethane having average C-Cl bond
length 1.783 Å and some other bond lengths
shown in table A.
As the electronegativity of chlorine atom is very high than
hydrogen therefore, in chloromethane the carbon will direct
a hybrid orbital high in p character towards chlorine. On the
other hand orbitals have high s character direct towards the
hydrogen.
Bond length is proportional to % of s character.
Table A : bond length
5. Application of bent rule
• Bond angle : Bent rule can explain the
difference in the bond angles of
molecules from ideality. The relation
between the hybridization of central
metal atom and bond angle can be
explain by taking example of methane.
According to bent rule, as the electronegativity
of the substituent increases, orbitals having
greater p character will be directed towards
those groups and hence the bond angle
decreases. It suggests that the hybrid orbital
having more s character should be directed
towards the hydrogen having more p
character.
Bond angle is proportional to % s character.
