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Heterolysis (chemistry)
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<p>In <a href="/facts/Chemistry/SrNqkGVm">chemistry</a>, heterolysis or heterolytic fission is the process of cleaving/breaking a <a href="/facts/Covalent_bond/EzMLf3Pz">covalent bond</a> where one previously bonded <a href="/facts/Chemical_species/A8BxM3oW">species</a> takes both original bonding <a href="/facts/Electron/L0KBo5cW">electrons</a> from the other species. During heterolytic bond cleavage of a neutral molecule, a <a href="/facts/Cation/wrbwhF3z">cation</a> and an <a href="/facts/Anion/wrbwhF3z">anion</a> will be generated. Most commonly the more <a href="/facts/Electronegativity/H7Vq7Uah">electronegative</a> atom keeps the pair of electrons becoming anionic while the more electropositive atom becomes cationic. </p> <p>Heterolytic fission almost always happens to <a href="/facts/Single_bond/8qz02fEl">single bonds</a>; the process usually produces two fragment species. </p><p>The energy required to break the bond is called the heterolytic <a href="/facts/Bond_dissociation_energy/wdDb5yHN">bond dissociation energy</a>, which is similar (but not equivalent) to homolytic bond dissociation energy commonly used to represent the <a href="/facts/Bond_energy/q4be3EeR">energy value</a> of a bond. </p><p>One example of the differences in the energies is the energy required to break a H−H bond </p> <table><tbody><tr><td> H 2 ⟶ 2 H ⋅ {\displaystyle {\ce {H2 -> 2H.}}} </td><td></td><td>Δ<i>H</i> = 104 kcal/mol</td></tr><tr><td> H 2 ⟶ H + + H − {\displaystyle {\ce {H2 -> H+ + H-}}} </td><td></td><td>Δ<i>H</i> = 66 kcal/mol (in water)</td></tr></tbody></table>