Question

12. lonisation energy decreases on moving from lithium bowand cesium. Why?
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Answer 1

As mentioned before, in each of the elements Group 1, the outermost electrons experience a net charge of +1 from the center. However, the distance between the nucleus and the outer electrons increases down the group; electrons become easier to remove, and the ionization energy falls.

Answer 2

Explanation:

Ionisation energy is defined as a energy required to remove outermost electron from an atom

Reason For I.E decrease when moving from Li to Cs

1. In an atom, electron and proton are bound together by their electrostatic force of attraction
2. If electrostatic force between electron and proton is more then that electron will be tightly bounded to an atom
3. As per columb law of electrostatic force, Electrostatic force is inversely proportional to square of distance between the charges
4. We know that atomic size increase from Li to Cs so the distance between outermost electron and proton also increase so their mutual Force of attraction decreases
5. If Mutual force of attraction decreases then that outermost electron are loosely binded to an atom
6. So if we provide a small of Energy to that outermost Electron then that electron will leave the orbital
7. So I.E decreases from Li to Cs due to increase in atomic size from Li to Cs