# Modern periodic table question-B

Dear student,

Ionisation energy or ionisation enthalpy is the energy required to remove an electron from the isolated gaseous neutral atom to form a positively charged ion.

First Ionization Energy, energy needed to remove the outermost or highest energy, electron from a neutral atom in the gas phase.

Li $\stackrel{}{\to }$Li+  + e-

Coming to the query,

​Both Li  and F belong to the same period (Period 2).

Electronic configuration of :
• Li : 1s22s1
• F : 1s22s22p5
Lithium can easily lose an electron to acquire stable noble gas configuration of 1s2​​​​​​​ but Fluorine , even though has a small size , has higher electron density of nine electrons in its ultimate or valence shell making it unstable, thus it requires a higher ionisation enthalpy as compared to Lithium to lose an electron from its atom.

Regards.

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