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Bond order
Bond order

Bond order is the number of bonds between a pair of atoms. For example in nitrogen N=N the bond order is 3, in acetylene H-C=C-H the bond order between the two carbon atoms is also 3 and the C-H bond order is 1....
 is the number of bonds between a pair of atoms. For example in nitrogen
Nitrogen

Nitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674?. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere....
 N=N the bond order is 3, in acetylene
Acetylene

Acetylene is the chemical compound with the symbol carbonhydrogen. It is the simplest alkyne.As an alkyne, acetylene is Saturation because its two carbon atoms are Chemical bond together in a triple bond....
 H-C=C-H the bond order between the two carbon atoms is also 3 and the C-H bond order is 1. Bond order gives an indication to the stability of a bond. In a more advanced context, bond order need not be an integer. A good example of this is bonds between carbon in the molecule benzene
Benzene

Benzene, or benzol, is an organic compound chemical compound and a known carcinogen with the molecular formula Carbon6Hydrogen6....
 where the delocalized molecular orbitals contain 6 pi electrons over six carbons essentially yielding half a pi bond
Pi bond

In chemistry, pi bonds are covalent bond chemical bonds where two lobes of one involved electron atomic orbital overlap two lobes of the other involved electron orbital....
.






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Bond order
Bond order

Bond order is the number of bonds between a pair of atoms. For example in nitrogen N=N the bond order is 3, in acetylene H-C=C-H the bond order between the two carbon atoms is also 3 and the C-H bond order is 1....
 is the number of bonds between a pair of atoms. For example in nitrogen
Nitrogen

Nitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674?. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere....
 N=N the bond order is 3, in acetylene
Acetylene

Acetylene is the chemical compound with the symbol carbonhydrogen. It is the simplest alkyne.As an alkyne, acetylene is Saturation because its two carbon atoms are Chemical bond together in a triple bond....
 H-C=C-H the bond order between the two carbon atoms is also 3 and the C-H bond order is 1. Bond order gives an indication to the stability of a bond. In a more advanced context, bond order need not be an integer. A good example of this is bonds between carbon in the molecule benzene
Benzene

Benzene, or benzol, is an organic compound chemical compound and a known carcinogen with the molecular formula Carbon6Hydrogen6....
 where the delocalized molecular orbitals contain 6 pi electrons over six carbons essentially yielding half a pi bond
Pi bond

In chemistry, pi bonds are covalent bond chemical bonds where two lobes of one involved electron atomic orbital overlap two lobes of the other involved electron orbital....
. Together with the sigma bond
Sigma bond

In chemistry, sigma bonds are the strongest type of covalent bond chemical bond. Sigma bonding is most clearly defined for diatomic molecules using the language and tools of symmetry groups....
 the bond order is 1.5. Furthermore bond orders of 1.1 for example can arise under complex scenarios and essentially refer to bond strength relative to bonds with order 1.

In molecular orbital theory
Molecular orbital theory

In chemistry, molecular orbital theory is a method for determining molecular structure in which electrons are not assigned to individual chemical bonds between atoms, but are treated as moving under the influence of the nuclei in the whole molecule....
 bond order is also defined as the difference, divided by two, between the number of bonding electrons and the number of antibonding electrons per the equation below. This often but not always yields the same result. Bond order is also an index of bond strength
Bond strength

In chemistry, bond strength is measured between two atoms joined in a chemical bond . It is the degree to which each atom linked to a central atom contributes to the valency of this central atom....
 and is also used extensively in valence bond theory
Valence bond theory

In chemistry, valence bond theory is one of two basic theories, along with molecular orbital theory, that developed to use the methods of quantum mechanics to explain chemical bond....
.



For example, the bond order concept is used in molecular dynamics
Molecular dynamics

Molecular dynamics is a form of computer simulation in which atoms and molecules are allowed to interact for a period of time by approximations of known physics,...
 bond order potential
Bond order potential

Bond order potentials are a class of empirical potentials used e.g. in molecular dynamics and molecular statics simulations. Examples include the Jerry Tersoff potential...
s.

The magnitude of the bond order is associated with the bond length. According to Pauling (1947), the bond order is experimentally described by:



Where is the bond length experimentally measured, is the single bond length, and b is a constant, depending on the atoms. Pauling suggested a value of 0.353 for b.

The above definition of bond order is somewhat ad hoc and only easy to apply for diatomic molecules. A standard quantum mechanical definition for bond order has been debated for a long time. The latest definition given by IUPAC replaces the old definitions .