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What is a chemical bond?
When atoms, ions, or molecules come together, they create chemical compounds because of a long-term attraction. Electrostatic interaction between ions with opposing charges forms ionic bonds, whereas electron sharing forms covalent bonds.
In chemistry, the strength of chemical bonds varies; there are “strong bonds” and “secondary bonds,” such as the covalent, ionic, and metallic bonds.
Sigma bonds can be homolytic or heterolytic depending on the energy of their triplet and singlet excitations. The excitation energy of a metal-metal sigma bond is so high that it cannot be seen.
However, chemists may use simplification techniques to estimate bond strength, directionality, and polarity based on quantum theory.
An atom-to-atom attraction constitutes a chemical bond. The variations in the behaviour of the atoms’ outermost or valence electrons can account for this attraction. In a wide range of contexts, these behaviours blend into one another, making it difficult to tell them apart. It is a common practice to distinguish between distinct types of bonds, which have different properties in condensed matter.
Cleavage of Bonds
The splitting of chemical bonds is known as bond cleavage or bond fission.
Bond cleavage is divided into two categories: homolytic and heterolytic, depending on the nature of the process. A sigma bond’s triplet and singlet excitation energies can be used to determine whether a bond will follow a homolytic or heterolytic pathway. A metal-metal sigma bond is an exception because the excitation energy of the bond is extremely high, making it unsuitable for observation.
Homolytic Bond Cleavage
The two electrons in a cleaved covalent bond are divided equally between the products in homolytic cleavage or homolysis. This is also known as radical fission or homolytic fission. A bond’s bond-dissociation energy is the amount of energy required to homolytically cleave the bond. One measure of bond strength is the enthalpy change.
The homolytic cleavage of oxygen-oxygen bonds in peroxides is one such example. These intramolecular bonds are relatively weak, implying that their bond dissociation energies are very low. As a result, only a small amount of heat energy is required to overcome this barrier.
Heterolytic bond Cleavage
The bond breaks in heterolytic cleavage, or heterolysis, in such a way that one of the fragments retains the originally-shared pair of electrons. As a result, one fragment gains an electron while the other loses an electron because it has both bonding electrons. Ionic fission is another name for this process.
The energy required for heterolytic dissociation is the singlet excitation energy of a sigma bond, but due to Coulombic attraction between the two ion fragments, the actual singlet excitation energy. Despite their bond strengths, the singlet excitation energy of a silicon-silicon sigma bond is lower than that of a carbon-carbon sigma bond because silicon has a higher electron affinity and lower ionisation potential than carbon.
The chemical species that did not retain any of the bonded electrons after the bond fission is known as the cation, which is the positively charged product of the heterolytic fission of a neutral molecule. The negatively charged heterolysis product (also known as the anion), on the other hand, is the chemical species that retains both bonded electrons after the bond fission process.
Example
A single acyclic structure can be formed by heterolytic cleavage of one of the polar carbon-oxygen bonds in an epoxide ring.
Difference between homolytic and heterolytic cleavage
The main difference between homolytic and heterolytic fission is that homolytic fission gives each fragment one bond electron, whereas heterolytic fission gives one fragment two bond electrons and the other fragment none.
Homolytic cleavage | Heterolytic cleavage | |
|---|---|---|
Definition | The dissociation of a chemical bond into two equal fragments is known as homolytic fission. | The dissociation of a chemical bond into two unequal fragments is known as heterolytic fission. |
Product | It forms 2 equal fragments | It forms 2 unequal fragments |
Bond Electrons | give one bond electron to each fragment | one fragment receives two bond electrons, while the other fragment receives none. |
Energy | that is either absorbed or released during homolytic fission is homolytic bond dissociation energy | Heterolytic bond dissociation energy is the energy absorbed or released during heterolytic fission. |
Conclusion
The energy of the triplet and singlet excitations of a sigma bond can determine whether it will follow a homolytic or heterolytic pathway. A metal-metal sigma bond is an exception because the bond’s excitation energy is so high that it’s impossible to observe.
The negatively charged electrons orbiting the nucleus and the positively charged protons in the nucleus are attracted to each other due to a simple electromagnetic force. An electron positioned between two nuclei will be attracted to both of them, and nuclei in this position will be attracted to electrons. The chemical bond is formed by this attraction.
