The breaks in the trend of increasing second and third ionization enthalpy occur for Mn²⁺ and Fe³⁺ in the 3d series, where these ions have d⁵ configuration. Similar breaks occur at corresponding elements in later transition series, and these anomalies are attributed to the unique electronic configurations of these ions, deviating from the expected increase in ionization enthalpies.
Why does the trend of increasing second and third ionization enthalpy experience breaks for the formation of Mn²⁺ and Fe³⁺ in the 3d series, and what is the significance of these breaks?
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The trend of increasing second and third ionization enthalpy experiences breaks for the formation of Mn²⁺ and Fe³⁺ in the 3d series because both ions have d⁵ configurations. At d⁵ configuration, there is no loss of exchange energy, which increases the stability of the electronic configuration. The absence of loss in exchange energy results in a lower ionization enthalpy for Mn²⁺ compared to Cr⁺ and Fe³⁺ compared to Mn²⁺. These breaks are significant as they deviate from the expected trend based on the increase in effective nuclear charge, emphasizing the unique electronic configurations’ influence on ionization enthalpies in the 3d series.