Question

How much energy is required to ionise a H atom if the electron occupies n = 5 orbit? Compare your answer with the ionization enthalpy of H atom ( energy required to remove the electron from n = 1 orbit).

Answer 1

ionisation energy is given by, $I.E=13.6\frac{Z^2}{n^2}eV$

where Z is atomic number of atom, n is orbit number from which an electron is removed.

here, Z = 1 [ as hydrogen atom ] and n = 5

so, ionisation energy or amount of energy required to ionise H-atom $E_{n=5}$= 13.6 × 1²/(5)² = 0.544eV

and amount of energy required to ionise H -atom from (n = 1 orbit), $E_{n=1}$= 13.6 × 1²/1²

= 13.6eV

here, $\frac{E_{n=1}}{E_{n=5}}=25$ means, ionisation enthalpy of H atom for n = 1 is 25 times ionisation enthalpy of H-atom for n = 5.