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

Explanation

Energy for a hydrogen electron present in a particular energy shell,
`E_(n)=-(13.12)/(n^(2))xx10^(5)J mol^(-1)=-(13.12xx10^(5))/(n^(2)xx6.022xx10^(23))J "atom"^(-1)`
`=(-2.18xx10^(-18))/(n^(2))J "atom"^(-1)`
Step I. Ionisation energy for hydrogen electron present in orbit n=5
`IE_(5)=E_(oo)-E_(5)=0-((-2.18xx10^(-18))/(25))J "atom"^(-1)=8.72xx10^(-20)J "atom"^(-1)`
Step II . Ionisation energy for hydrogen electron present in orbit n=1
`IE_(1)=E_(oo)-E_(1)=0-((-2.18xx10^(-18))/(1))=2.18xx10^(-18) J "atom"^(-1)`
On comparing : `(IE_(1))/(IE_(5))=((2.18xx10^(-18)J "atom"^(-1)))/((8.72xx10^(-20)"Jatom"^(-1)))=25`
The energy required to remove an electron from first orbit in a hydrogen atom is 25 times the energy needed to remove an electron from fifth orbit.