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How would you explain the fact that first ionisation enthalpy of sodium is lower than that of magnesium but its second ionisation enthalpy is higher than that of magnesium?

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प्रश्न

How would you explain the fact that first ionisation enthalpy of sodium is lower than that of magnesium but its second ionisation enthalpy is higher than that of magnesium?

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उत्तर

Electronic configuration of \[\ce{Na}\] is 1s22s22p63s1. After losing one electron from its outermost shell, sodium easily attains stable electronic configuration (1s22s22p), while magnesium does not lose its electron easily due to presence of two electrons in s-orbital (1s22s22p63s2). Hence first ionisation energy of sodium is less than magnesium.

When one electron is removed from \[\ce{Na}\] and \[\ce{Mg}\], their configurations become ls22s22p6 and 1s22s22p63s1 respectively. Now it is easier to remove one electron from 3s of \[\ce{Mg+}\] than 2p6 of \[\ce{Na+}\]. Hence, second ionisation energy of \[\ce{Mg}\] is less than \[\ce{Na}\].

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अध्याय 3: Classification of Elements and Periodicity in Properties - Multiple Choice Questions (Type - I) [पृष्ठ ३३]

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एनसीईआरटी एक्झांप्लर Chemistry [English] Class 11
अध्याय 3 Classification of Elements and Periodicity in Properties
Multiple Choice Questions (Type - I) | Q 35 | पृष्ठ ३३

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