B.sc 1st year Book (Page 7)
Odd electron bond
One electron bond :
(a) <—–> (b) =>Reserince hybrid
Three electron bonds:
He2+ ion :
This ion is represented as a resonance hybrid of (a) and (b) respectively.
The bond energy of one electron bond and three electron bonds ars nearly identical. The bond length of the He2+ ion is equal to 58Kcal/mole.
O2 molecule :
Generally, it is considered that the O2 molecule is formed by sharing of two electrons each: between two oxygen atoms, Thus, the O2 molecule should be diamagnetic, while this molecule Is paramagnetic. It is, therefore, assumed that in this molecule two electrons are involved in a single covalent bond formation between the two O-atoms, and the remaining 6 electrons (three of each O-atom) form two 3 electrons bonds. as shown below:
Thus, this molecule is called a double odd molecule. The paramagnetic behavior of this molecule is also confirmed by M.O.theory, The molecular orbital electronic configuration of the O2 molecule shows there are two unpaired electrons present in antibonding p-molecular orbitals as shown below:
NO molecule :
Nitric oxide is the most stable odd molecule. Its valence bond representation is given as :
Structure(b) is expected to be less stable as compared to structure(a) because of the distribution of unfavorable charges, i.e., we are placing a positive charge on a more electronegative oxygen atom. However, structures(a) and (b) both have nearly equal stability and thus there is complete resonance(structure c) between the two structures. This resonating hybrid structure shows NO molecule consists one double bond and one 3-electron bond. Thus, due to the presence of one odd electron bond NO molecule is paramagnetic:
This molecule exists in two resonating forms, both forms have equal stability. These structures shows of the ClO2 molecule consists of one 3 – electrons bond between either one of the Cl−O bond: In this case, the central Cl atom contributes one electron and one of the neighboring oxygen atoms contributes two electrons in odd bond formation,
Thus, this molecule is paramagnetic.
NO2 molecule :
This molecule also exists in two resonating forms, both forms have equal stability, In this case, the central N atom contributes two electrons, and one of the neighboring oxygen atoms contributes only one electron in odd bond formation.
Related Topic | Chemical Bonding
|Chemical Bonding||Inert Pair Effect|
|Lattice energy||Fajans Rule|
|Covalent Bond||Coordinate Bond|
|Odd electron bond||Metallic bond|
|Hydrogen Bonding||M.O. Theory|
|Sidgwick-Powell theory||VSEPR theory|
|Hybridization of atomic orbitals|
Characteristics of three electron bonds:
(i) It has been found that three electrons bond can never be formed if the electronegativity difference exceeds 0.5. If there is a large difference in electronegative value the molecule will be unstable.
(ii) Three_electron bond must have a greater bond length as compared to two electrons bond and possess lesser bond energy.
(iii) This type of bond forms a hybrid between two extreme structures.
(v) The three electrons borid is one and a half as an electron pair bond.
(vi) An odd bond is mostly equivalent to one-half of the normal covalent bond.
(vii) Most of the compounds which have three electrons bond are colored and show paramagnetic behavior.