Why is the ionization potential of helium more than fluorine's and the electron affinity of chlorine more than fluorine's?

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jerichorayel | College Teacher | (Level 2) Senior Educator

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Ionization energy is the energy required to remove a single electron from an atom or molecule it the gaseous state. However, the energy required to remove an electron governs certain factors. It is easier to remove an electron from a partially filled orbital than that of fully filled orbital. It is also easier to remove an electron which is farther from the nucleus. Helium has a completely filled s orbital, Fluorine has incomplete orbital. The valence electrons of helium are nearer to its nucleus than that of the valence electrons of fluorine.

Electron affinity is the energy released when an electron is added to a neutral atom. Though the trend should be decreasing down the group, chlorine has larger electron affinity than fluorine. This is because the fluoride ion is much less stable than chloride ion.