Which of the following has the lowest ionization energy (Na, K, Cs)?

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  • 1 decade ago
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    ionization energy is the amount of energy required to remove one mole electrons form one mole gaseeous atoms. now considering Na,K and Cs. Na is in the 3rd period, K in the 4th Period and Cs in the 5th period, so they will have their valence electron in 3rd 4th and 5th orbit respectively. now as you go away from the nucleus the attraction toward nucleus decreases so easily an electron can be removed. so as Cs will have its outermost electron in 5th orbit which will be away from nucleus compared to K and Na so Cs will have lowest ionisation energy

    hope this explanation will help you out

    Source(s): myself chemistry teacher
  • 1 decade ago

    Cs because ionization energy decreases as you go down the periodic table, and increases as you go accross.

    for example: lowest ionization energy for ( B , C) = B

    ( O, S) = S

    (Cl , As) = Cl

    I hope few other examples of mine, helps you understand better.

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