Bond Order and How to Calculate Bond Order
Bond Order
Bond order is a term used to describe the strength and stability of a chemical bond between two atoms. It is an important concept in chemistry as it helps to predict the properties and reactivity of molecules.
The concept of bond order was first introduced by Linus Pauling in the early 1930s. He defined bond order as the number of shared electron pairs between two atoms in a molecule. It is denoted by the symbol 'B' and is typically represented as a whole number. A higher bond order indicates a stronger bond between two atoms.
Bond order is directly related to the bond length and bond energy of a molecule. In simple terms, the shorter the bond length, the higher the bond order, and the stronger the bond. Likewise, a higher bond energy corresponds to a higher bond order and a more stable bond. This is because a higher bond order indicates a greater degree of overlap between the atomic orbitals, resulting in a stronger attraction between the two atoms.
Bond order is also important in understanding the molecular geometry of a compound. According to the Valence Shell Electron Pair Repulsion (VSEPR) theory, the bond order between two atoms determines the shape of the molecule. For instance, a bond order of 1 results in a linear shape, while a bond order of 2 results in a bent shape.
One of the most common applications of bond order is in predicting the behavior of molecules in chemical reactions. In general, molecules with a higher bond order are more stable and less reactive than those with a lower bond order. This is because a higher bond order indicates a stronger bond, which is difficult to break or manipulate.
Furthermore, bond order is crucial in understanding the strength of intermolecular forces between molecules. In molecules held together by weak intermolecular forces, such as van der Waals forces, the bond order is low. On the other hand, molecules with strong covalent bonds exhibit a higher bond order.
The calculation of bond order can also provide insights into the electronic structure of a molecule. Bond order is closely related to the concept of molecular orbital theory, which describes the distribution of electrons in a molecule. In this theory, a higher bond order corresponds to a greater number of bonding electrons occupying the molecular orbitals.
The determination of bond order is not limited to simple diatomic molecules. It can also be applied to more complex molecules with multiple bonds. In such cases, the bond order is calculated by taking the average of the bond orders for each bond present in the molecule.
How to Calculate Bond Order
For simple molecules, the bond order is calculted by a simple formula given below-
Bond Order(B.O.) = 1/2[Number of bonding electrons − Number of antibonding electrons]
Bond Order Calculator
Examples-
Bond Order in H2 molecule-
Bond Order = 1/2[2 − 2] = 1
Bond order one indicates that the two hydrogen atoms are linked with each other by a single bond.
H − H
Bond Order in O2 molecule-
Bond Order = 1/2[6 − 2] = 2
Bond order two indicates that the two oxygen atoms are linked with each other by a double bond.
O = O
Bond Order in N2 molecule-
Bond Order = 1/2[6 − 0] = 3
Bond order three indicates that the two oxygen atoms are linked with each other by a triple bond.
N ≡ N
The method mentioned above based on Molecular orbital theory(MOT) is time consuming. A new innvative method has been introduced to calculate the bond order of molecules and ions having total electrons 8 to 20 in a very simple way. This method is not applicable for polyatomic molecules such as BF3, CH4, CO2 etc. and is applicable for mono +2 etc. Another method has also to be introduced for atomic and diatomic molecules ans ions such as CO, NO+, O2 determination of bond order of oxides based acid radicals in a very simple way.
First of all one should slassify the molecules or ions into two types based on total number of electrons.
A. Molecules and ions having total number of electrons with in the range 8 - 14.
Examples: Be2(Total Electrons = 8), B2(Total Electrons = 10), C2(Total Electrons = 12), C2−(Total Electrons = 13), C2+(Total Electrons = 11), N2(Total Electrons = 14), N2+(Total Electrons = 13), O2+2(Total Electrons = 14), CO(Total Electrons = 14), NO+(Total Electrons = 14).
B. Molecules and ions having total number of electrons with in the range 15 - 20.
Examples: N2−(Total Electrons = 15), 02(Total Electrons = 16), O2+(Total Electrons = 15), O2−2(Total Electrons = 18), F2(Total Electrons = 18), Ne2(Total Electrons = 20).
New method for determination of bond order of molecules and ions having total number of electrons with in the range of 8 to 14 electrons.
Bond Order = [N − 8] / 2
Where N = Total number of elecrons.
Examples:
Be2
Total electrons = 8
So, Bond Order = [8 − 8]/2 = 0
That means He2 does not exist.
C2
Total electrons = 12
So, Bond Order = [12 − 8]/2 = 2
C2−
Total electrons = 13
So, Bond Order = [13 − 8]/2 = 2.5
C2+
Total electrons = 11
So, Bond Order = [11 − 8]/2 = 1.5
N2
Total electrons = 14
So, Bond Order = [14 − 8]/2 = 3
N2+
Total electrons = 13
So, Bond Order = [13 − 8]/2 = 2.5
CO
Total electrons = 14
So, Bond Order = [14 − 8]/2 = 3
NO+
Total electrons = 14
So, Bond Order = [14 − 8]/2 = 3
CN+
Total electrons = 12
So, Bond Order = [12 − 8]/2 = 2
CN−
Total electrons = 14
So, Bond Order = [14 − 8]/2 = 3
New method for determination of bond order of molecules and ions having total number of electrons with in the range of 15 to 20 electrons.
Bond Order = [20 − N] / 2
Where N = Total number of elecrons.
Examples:
N2−
Total electrons = 15
So, Bond Order = [20 − 15]/2 = 2.5
O2
Total electrons = 16
So, Bond Order = [20 − 16]/2 = 2
O2−
Total electrons = 17
So, Bond Order = [20 − 17]/2 = 1.5
O2−2
Total electrons = 18
So, Bond Order = [20 − 18]/2 = 1
NO
Total electrons = 15
So, Bond Order = [20 − 15]/2 = 2.5
F2
Total electrons = 18
So, Bond Order = [20 − 18]/2 = 1
Ne2
Total electrons = 20
So, Bond Order = [20 − 20]/2 = 0
That means Ne2 does not exist.
New method for determination of Bond Order of Oxide based Acid Radials
In case of Acid Radicals-
Bond Order = Valency of Peripheral Atom + (Charge on Acid Radical ÷ Number of Peripheral Atoms)
This formula is very very important for NEET, IIT-JEE, GATE, IIT-JAM, CSIR, SLET, DRDO, TIFR, ICT, IISc, and other entrance exams.
SO4−2:
Valency of peripheral atom (i.e. oxygen) = 2
Charge on acid radical = −2
Number of peripheral atoms = 4
So, the Bond Order = 2 + (−2 ÷ 4) = 1.5
SO3−2:
Valency of peripheral atom (i.e. oxygen) = 2
Charge on acid radical = −2
Number of peripheral atoms = 3
So, the Bond Order = 2 + (−2 ÷ 3) = 1.33
PO4−3:
Valency of peripheral atom (i.e. oxygen) = 2
Charge on acid radical = −3
Number of peripheral atoms = 4
So, the Bond Order = 2 + (−3 ÷ 4) = 1.25
MnO4−:
Valency of peripheral atom (i.e. oxygen) = 2
Charge on acid radical = −1
Number of peripheral atoms = 4
So, the Bond Order = 2 + (−1 ÷ 4) = 1.75
NO3−:
Valency of peripheral atom (i.e. oxygen) = 2
Charge on acid radical = −1
Number of peripheral atoms = 3
So, the Bond Order = 2 + (−1 ÷ 3) = 1.66
NO2−:
Valency of peripheral atom (i.e. oxygen) = 2
Charge on acid radical = −1
Number of peripheral atoms = 2
So, the Bond Order = 2 + (−1 ÷ 2) = 1.5
BO3−3:
Valency of peripheral atom (i.e. oxygen) = 2
Charge on acid radical = −3
Number of peripheral atoms = 3
So, the Bond Order = 2 + (−3 ÷ 3) = 1
CO3−2:
Valency of peripheral atom (i.e. oxygen) = 2
Charge on acid radical = −2
Number of peripheral atoms = 3
So, the Bond Order = 2 + (−2 ÷ 3) = 1.33
ClO4−:
Valency of peripheral atom (i.e. oxygen) = 2
Charge on acid radical = −1
Number of peripheral atoms = 4
So, the Bond Order = 2 + (−1 ÷ 4) = 1.75
SiO4−4:
Valency of peripheral atom (i.e. oxygen) = 2
Charge on acid radical = −4
Number of peripheral atoms = 4
So, the Bond Order = 2 + (−4 ÷ 4) = 1
Relation of Bond Order with Bond Length, Bond Strength, Bond Dissociation Energy, Thermal Stability and Reactivity
✍︎ Bond order is inversely proportional to Bond Length✍︎ Bond order is directly proportional to Bond Strength
✍︎ Bond order is directly proportional to Bond Dissociation Energy
✍︎ Bond order is directly proportional to Thermal Stability
✍︎ Bond order is inversely proportional to Reactivity
